CORE SKILLS SCIENCE (KNOWLEDGE REQUIREMENT)

Temperature measurement scales

IVQs in Engineering Skills (1155)Level 1 IVQ Certificate in Engineering Skills(1155-01) (500/5817/4)

On completion of this lesson you will be able to State the fix points on the

Celsius (Centigrade), Fahrenheit and Kelvin scales (4.1)

Fixed Point:

A fixed point (sometimes shortened to fix point, also known as an invariant point) of a function is a point that is mapped to itself by the function.

Temperature Scales & Fixed Points

The Origins of Fixed Temperature Points:

When the thermometer was first invented there was no clear understanding of fixed temperature points. To further confuse the situation the skills required to make thermometers were not available: it was difficult to make a thermometer with a bore of consistent diameter along its length, meaning that no two thermometers were alike. It was only when people travelled with individual thermometers that they were able to confirm that the fixed points of water boiling and freezing were the same in different locations and the effects of altitude and air pressure were recognized. The boiling and freezing points of water were chosen as fixed points because they were easily achievable.

Once the fixed points had been recognized and thermometer making skills had improved, the way was clear for a widely recognized temperature scale. Many were proposed and the main ones are outlined below.

Fixed Point of Celsius scale:

The Celsius Scale

While Celsius's original metric scale had to be inverted before it came into common use, it still bears his name today. The Celsius scale is widely used today for science, engineering and meteorological purposes. Fixed Points: Freezing Point of Water

Boiling Point of Water

Number of Divisions: 100 degrees

Notes: In 1742 Swedish scientist Anders Celsius chose 0 degree for the boiling point of water, and 100 degrees for the freezing point. A year later, the Frenchman Jean Pierre Cristin (1683-1755) inverted the Celsius scale to produce the Centigrade .scale used today (freezing point 0°, boiling point 100°). By international agreement in 1948 Cristin's adapted scale became known as Celsius and is still in use today.

Fixed Point of Fahrenheit scale:

The Fahrenheit Scale

This was the first widely used temperature scale and it is still in use today, though it has lost popularity as people have moved towards metric measurements.

Fixed Points: Freezing Point of Water Boiling Point of Water

Number of Divisions:

180 degrees

32 was chosen as the figure for the lower fixed point as this produced a scale that would not fall below zero even when measuring the lowest possible temperatures that he could produce in his laboratory - a mixture of ice, salt and water.

Fixed Point of Kelvin scale

The Kelvin Scale The Kelvin is the standard SI unit of thermodynamic temperature in use today.

Celsius scale of Temperature

It is most commonly used by physicists.Fixed Points:Triple Point of Water

Boiling Point of Water

Number of Divisions:100 degrees

In 1848 Sir William Thomson, Baron Kelvin of Larges, Lord Kelvin of Scotland (1824 - 1907) proposed the absolute temperature scale with zero degrees being the theoretical lowest temperature possible where molecular motion ceases. Kelvin defined 1 Kelvin degree as being equal to one Celsius degree.

Fixed points in use today

The practical temperature scale in use today is maintained by the General Conference on Weights & Measures (Paris). The most recent temperature scale was devised in 1990: The International Temperature Scale of 1990 or ITS-90 for short. ITS-90 covers 16 fixed points, being the melting, freezing or triple points of various substances: Water, Mercury, Gallium, Indium, Tin, Zinc, Aluminum, Silver Hydrogen, Neon, Oxygen, Argon, Copper and Gold. Water apart, all of these are elements. These fixed points give a range of temperatures at which a thermometer can be calibrated from, for example, the triple point of Hydrogen at -259.3467°C (13.8033 K ) to the freezing point of Gold at 1064.16°C ( 1337.33K ).

4.2 Identify, compare and describe the use of approximate and precise workshop methods of temperature measurement. Temperature measurement: Thermometer (Mercury in glass) heat sensitive paint b or crayons, fusible salts or

cones, estimation by colour oxides layer colour, other approximate workshop methods, thermocouple and optical pyrometer.

Many methods have been developed for measuring temperature. Most of these rely on measuring some physical property of a working material that varies with temperature. One of the most common devices for measuring temperature is the glass thermometer. This consists of a glass tube filled with mercury or some other liquid, which acts as the working fluid. Temperature increases cause the fluid to expand, so the temperature can be determined by measuring the volume of the fluid. Such thermometers are usually calibrated so that one can read the temperature simply by observing the level of the fluid in the thermometer. Another type of thermometer that is not really used much in practice, but is important from a theoretical standpoint, is the gas thermometer.

Other important devices for measuring temperature include:

Thermocouples Thermistors Resistance Temperature Detector (RTD) Pyrometer Langmuir probes (for electron temperature of a plasma) Infrared thermometer.

One must be careful when measuring temperature to ensure that the measuring instrument (thermometer, thermocouple, etc.) is really at the same temperature as the material that is being measured. Under some conditions heat from the measuring instrument can cause a temperature gradient, so the measured temperature is different from the actual temperature of the system. In such a case the measured temperature will vary not only with the temperature of the system, but also with the heat transfer properties of the system. An extreme case of this effect gives rise to the wind chill factor, where the weather feels colder under windy conditions than calm conditions even though the temperature is the same. What is happening is that the wind increases the rate of heat transfer from the body, resulting in a larger reduction in body temperature for the same ambient temperature.

The theoretical basis for thermometers is the zeroth law of thermodynamics which postulates that if you have three bodies, A, B and C, if A and B are at the same temperature, and B and C are at the same temperature then A and C are at the same temperature. B, of course, is the thermometer.

The practical basis of thermometry is the existence of triple point cells. Triple points are conditions of pressure, volume and temperature such that three phases (matter) are simultaneously present, for example solid, vapor and liquid. For a single component there are no degrees of freedom at a triple point and any change in the three variables results in one or more of the phases vanishing from the cell. Therefore, triple point cells can be used as universal references for temperature and pressure.

Under some conditions it becomes possible to measure temperature by a direct use of the Planck's law of black body radiation. For example, the cosmic microwave background

temperature has been measured from the spectrum of photons observed by satellite observations such as the WMAP. In the study of the quark-gluon plasma through heavy-ion collisions, single particle spectra sometimes serve as a thermometer.

Surface air temperatureMeteorological observatories measure the temperature and humidity of the air near the surface of the Earth usually using thermometers placed in a Stevenson screen, a standardized well-ventilated white-pained instrument shelter. The thermometers should be positioned 1.25–2 m above the ground. Details of this setup are defined by the World Meteorological Organization (WMO).

The true daily mean, obtained from a thermograph, is approximated by the mean of 24 hourly readings (which is not the same as the mean of the daily minimum and maximum readings).

The world's average surface air temperature is about 15 °C. For information on temperature changes relevant to climate change or Earth's geologic past see: Temperature record.

Comparison of temperature scalesMain article: Comparison of temperature scales

Comparison of temperature scales

CommentKelvin

KCelsius

°CFahrenheit

°FRankine°Ra (°R)

Delisle°D ¹

Newton°N ¹

Réaumur°R (°Ré, °Re) ¹

Rømer°Rø (°R) ¹

Absolute zero    0 −273.15 −459.67     0   559.725  −90.14 −218.52 −135.90

Lowest recorded natural temperature on Earth(Vostok, Antarctica - 21 July 1983)

 184  −89 −128   331   284  −29  −71  −39

Celsius /  233.15  −40  –40   419.67   210  –13.2  –32  –13.5

Fahrenheit's cross-over" temperature

Fahrenheit's  255.37  −17.78    0   459.67   176.67   −5.87  −14.22   −1.83

ice/salt mixture

Water freezes (at standard pressure)

 273.15    0   32   491.67   150    0    0    7.5

Average surface temperature on Earth

 288   15   59   519   128    5   12   15

Average human body temperature ²

 310.0 ±0.7

  36.8 ±0.7

  98.2 ±1.3

  557.9 ±1.3

   94.8 ±1.1

  12.1 ±0.2   29.4 ±0.6

  26.8 ±0.4

Highest recorded surface temperature on Earth(Al 'Aziziyah, Libya - 13 September 1922)But that reading is queried.

 331   58  136   596    63   19   46   38

Water boils (at standard pressure)

 373   100  212   672     0   33   80   60

Gas flame 1773 ~ 1500 ~ 2732 ~

Titanium melts 1941 1668 3034  3494 −2352  550 1334  883

The surface of the Sun

5800 5526 9980 10440 −8140 1823 4421 2909

1 The temperature scale is in disuse, and of mere historical interest.2 Normal human body temperature is 36.8 ±0.7 °C, or 98.2 ±1.3 °F. The commonly given value 98.6 °F is simply the exact conversion of the nineteenth-century German standard of 37 °C. Since it does not list an acceptable range, it could therefore be said to have excess (invalid) precision. See Temperature of a Healthy Human (Body Temperature) for more information.Some numbers in this table have been rounded off.

4.3 Identify typical temperatures for workshop operations,

Temperature for Soldering, brazing, braze welding, welding,

Hardening, Tempering and forging.

Temperature for soldering

A soldering iron is a hand tool most commonly used in soldering. It supplies heat to melt the solder so that it can flow into the joint between two work pieces.

A soldering iron is composed of a heated metal tip and an insulated handle. Heating is often achieved electrically, by passing an electric current (supplied through an electrical cord or battery cables) through the resistive material of a heating element. Another heating method includes combustion of a suitable gas, which can either be delivered through a tank mounted on the iron (flameless), or through an external flame. Less common uses include pyrography (burning designs into wood) and plastic welding.

Soldering irons are most often used for installation, repairs and limited production work. High-volume production lines use other soldering methods.

Soldering electronic components

For electrical work a low-power iron, a power rating between 15 and 30 watts, is used. Higher ratings are available, but do not run hotter; instead there is more power available for larger joints. Small battery-operated or gas soldering irons are useful when electricity is unavailable.

Temperature-controlled soldering station

A temperature-controlled soldering station consists of an electrical power supply and a soldering iron. It is most commonly used for soldering electronic components.

40/60 460 degrees F (230 degrees C)

50/50 418 degrees F (214 degrees C)

60/40 374 degrees F (190 degrees C)

63/37 364 degrees F (183 degrees C)

95/5 434 degrees F (224 degrees C)

Temperature for brazing

Brazing is a metal-joining process whereby a filler metal is heated above and distributed between two or more close-fitting parts by capillary action. The filler metal is brought slightly above its melting (liquids) temperature while protected by a suitable atmosphere, usually a flux. It then flows over the base metal (known as wetting) and is then cooled to join the work pieces together. It is similar to soldering, except the temperatures used to melt the filler metal is above 450 °C (842 °F), or, as traditionally defined in the United States, above 800 °F (427 °C).

The easiest way to categorize brazing methods is to group them by heating method. Here are some of the most common:

Torch brazing Furnace brazing Induction brazing Dip brazing

Resistance brazing Infrared brazing Blanket brazing Electron beam and laser brazing Braze welding

Temperature for braze welding

Braze welding

A braze-welded T-joint

Braze welding, also known as fillet brazing,[citation needed] is the use of a bronze or brass filler rod coated with flux to join steel work pieces. The equipment needed for braze welding is basically identical to the equipment used in brazing. Since braze welding usually requires more heat than brazing, acetylene or methylacetylene-propadiene (MPS) gas fuel is commonly used. The American Welding Society states that the name comes from the fact that no capillary action is used.

Temperature for hardening

Hardening and tempering (quenching and tempering)

Main article: Quenching

To harden by quenching, a metal (usually steel or cast iron) must be heated into the austenitic crystal phase and then quickly cooled. Depending on the alloy and other considerations (such as concern for maximum hardness vs. cracking and distortion), cooling may be done with forced air or other gas (such as nitrogen), oil, polymer dissolved in water, or brine. Upon being rapidly cooled, a portion of austenite (dependent on alloy composition) will transform to marten site, a hard, brittle crystalline structure. The quenched hardness of a metal depends on its chemical composition and quenching method. Cooling speeds, from fastest to slowest, go from polymer (i.e. silicon), brine, fresh water, oil, and forced air. However, quenching a certain steel too fast can result in cracking, which is why high-tensile steels such as AISI 4140 should be quenched in

oil, tool steels such as ISO 1.2767 or H13 hot work tool steel should be quenched in forced air, and low alloy or medium-tensile steels such as XK1320 or AISI 1040 should be quenched in brine or water. However, metals such as austenitic stainless steel (304, 316), and copper, produce an opposite effect when these are quenched: they anneal. Austenitic stainless steels must be quench-annealed to become fully corrosion resistant, as they work-harden significantly.

Untendered marten site, while very hard, is too brittle to be useful for most applications. A method for alleviating this problem is called tempering. Most applications require that quenched parts be tempered (heat treated at a low temperature, often 300 ˚F or 150 ˚C) to impart some toughness. Higher tempering temperatures (may be up to 1,300 ˚F or 700 ˚C, depending on alloy and application) are sometimes used to impart further ductility, although some yield strength is lost.

Temperature for Forging

Forging the Basic Principles

At its most basic level, forging is the process of forming and shaping metals through the use of hammering, pressing or rolling. The process begins with a cast ingot, which is heated to its plastic deformation temperature, then forged between dies to the desired shape and size.

During this hot forging process, the cast, coarse grain structure is broken up and replaced by finer grains, achieved through the size reduction of the ingot.

This produces a sound central region to the forged product and gives excellent overall structural integrity. Mechanical properties are therefore improved through the elimination of the cast structure, resulting in enhanced density and improved homogeneity.Forging also provides a means for aligning the grain flow to obtain the best desired directional strengths.

4.4 State sources of heat energy. Heat sources (Flame, electric

Arc, Electrical resistance)

4.5 Identify methods and applications of heat energy

Transmission.

Heat Energy

All matter is composed of tiny particles called molecules; most scientists believe that molecules are in a constant state of motion or vibration. They also believe that a body in motion posses’ kinetic energy and that the faster it moves the move kinetic energy it has. Moving molecules in matter represent kinetic energy that appears in the form of heat. The faster the molecules move, the more kinetic energy or heat there is in a particular substance. When the molecules of a substance slow down, there is less kinetic energy and substance heat.

Heat Transmission:

The fundamental modes of heat transfer are:

Conduction or diffusion The transfer of energy between objects that are in physical contact

Convection The transfer of energy between an object and its environment, due to fluid motion

Radiation The transfer of energy to / from a body, by means of the emission or absorption of electromagnetic radiation.

Mass transferThe transfer of energy from one location to another as a side effect of physically moving an object containing that energy

Conduction

On a microscopic scale, heat conduction occurs as hot, rapidly moving or vibrating atoms and molecules interact with neighboring atoms and molecules, transferring some of their energy (heat) to these neighboring particles. In other words, heat is transferred by conduction when adjacent atoms vibrate against one another, or as electrons move from one atom to another. Conduction is the most significant means of heat transfer within a solid or between solid objects in thermal contact. Fluids—especially gases—are less conductive. Thermal contact conductance is the study of heat conduction between solid bodies in contact.

Steady state conduction is a form of conduction that happens when the temperature difference driving the conduction is constant, so that after an equilibration time, the spatial distribution of temperatures in the conducting object does not change any further. In steady state conduction, the amount of heat entering a section is equal to amount of heat coming out.

Transient conduction occurs when the temperature within an object changes as a function of time. Analysis of transient systems is more complex and often calls for the application of approximation theories or numerical analysis by computer.

Convection

Convective heat transfer, or convection, is the transfer of heat from one place to another by the movement of fluids. (In physics, the term fluid means any substance that deforms under shear stress; it includes liquids, gases, plasmas, and some plastic solids.) Bulk motion of the fluid enhances the heat transfer between the solid surface and the fluid. Convection is usually the dominant form of heat transfer in liquids and gases. Although often discussed as a third method of heat transfer, convection actually describes the combined effects of conduction and fluid flow.

Free, or natural, convection occurs when the fluid motion is caused by buoyancy forces that result from density variations due to variations of temperature in the fluid. Forced convection is when the fluid is forced to flow over the surface by external means—such as fans, stirrers, and pumps—creating an artificially induced convection current.

Convection is described by Newton's law of cooling: "The rate of heat loss of a body is proportional to the difference in temperatures between the body and its surroundings."

Radiation

A red - hot iron object transferring heat to the surrounding environment primarily through thermal radiation.

Thermal radiation is energy emitted by matter as electromagnetic waves due to the pool of thermal energy that all matter possesses that has a temperature above absolute zero. Thermal radiation propagates without the presence of matter through the vacuum of space.

Thermal radiation is a direct result of the random movements of atoms and molecules in matter. Since these atoms and molecules are composed of charged particles (protons and electrons), their movement results in the emission of electromagnetic radiation, which carries energy away from the surface.

Unlike conductive and convective forms of heat transfer, thermal radiation can be concentrated in a small spot by using reflecting mirrors, which is exploited in concentrating solar power generation. For example, the sunlight reflected from mirrors heats the PS10 solar power tower and during the day it can heat water to 285 °C (545 °F).

Mass Transfer

In mass transfer, energy—including thermal energy—is moved by the physical transfer of a hot or cold object from one place to another. This can be as simple as placing hot water in a bottle and heating a bed, or the movement of an iceberg in changing ocean currents. A practical example is thermal hydraulics.

not heated.

Application of heat energy transmission

Applications and techniques

Heat transfer has broad application to the functioning of numerous devices and systems. Heat-transfer principles may be used to preserve, increase, or decrease temperature in a wide variety of circumstances.

Heat exchangers

A heat exchanger is a tool built for efficient heat transfer from one fluid to another, whether the fluids are separated by a solid wall so that they never mix, or the fluids are in direct contact. Heat exchangers are widely used in refrigeration, air conditioning, space heating, power generation, and chemical processing. One common example of a heat exchanger is a car's radiator, in which the hot coolant fluid is cooled by the flow of air over the radiator's surface.

Heat dissipation

A heat sink is a component that transfers heat generated within a solid material to a fluid medium, such as air or a liquid. Examples of heat sinks are the heat exchangers used in refrigeration and air conditioning systems, and the radiator in a car (which is also a heat exchanger). Heat sinks also help to cool electronic and optoelectronic devices such as CPUs, higher-power lasers, and light-emitting diodes (LEDs). A heat sink uses its extended surfaces to increase the surface area in contact with the cooling fluid.

Buildings

In cold climates, houses with their heating systems form dissipative systems. In spite of efforts to insulate houses to reduce heat losses via their exteriors, considerable heat is lost, which can make their interiors uncomfortably cool or cold. For the comfort of the inhabitants, the interiors must be maintained out of thermal equilibrium with the external surroundings. In effect, these domestic residences are oases of warmth in a sea of cold, and the thermal gradient between the inside and outside is often quite steep. This can lead to problems such as condensation and uncomfortable air currents, which—if left unaddressed—can cause cosmetic or structural damage to the property. Such issues can be prevented by use of insulation techniques for reducing heat loss.

Thermal energy storage

Thermal energy storage refers to technologies that store energy in a thermal reservoir for later use. They can be employed to balance energy demand between daytime and nighttime. The thermal reservoir may be maintained at a temperature above (hotter) or below (colder) than that of the ambient environment. Applications include later use in space heating, domestic or process hot water, or to generate electricity. Most practical active solar heating systems have storage for a few hours to a day's worth of heat collected

Evaporative cooling

Evaporative cooling is a physical phenomenon in which evaporation of a liquid, typically into surrounding air, cools an object or a liquid in contact with it. Latent heat describes the amount of heat that is needed to evaporate the liquid; this heat comes from the liquid itself and the surrounding gas and surfaces. The greater the difference between two temperatures, the greater the evaporative cooling effect. When the temperatures are the same, no net evaporation of water in air occurs; thus, there is no cooling effect. A simple example of natural evaporative cooling is perspiration, or sweat, which the body secretes in order to cool itself. An evaporative cooler is a device that cools air through the simple evaporation of water.

Radiative cooling

Radiative cooling is the process by which a body loses heat by radiation. It is an important effect in the Earth's atmosphere. In the case of the Earth-atmosphere system, it refers to the process by which long-wave (infrared) radiation is emitted to balance the absorption of short-wave (visible) energy from the Sun. Convective transport of heat and evaporative transport of latent heat both remove heat from the surface and redistribute it in the atmosphere, making it available for radiative transport at higher altitudes.

4.6 State that solids, Liquids and Gases expand when heated and

Contract when cooled.

Evaporation and Boiling (liquid to gas)

On heating particles gain kinetic energy and move faster and more able to overcome the intermolecular forces between the molecules i.e. some particles will have enough kinetic energy to overcome the attractive forces holding the particles together in the bulk liquid.

In evaporation* and boiling it is the highest kinetic energy molecules that can ‘escape’ from the attractive forces of the other liquid particles.

The particles lose any order and become completely free to form a gas or vapour. Energy is needed to overcome the attractive forces between particles in the liquid and is taken in

from the surroundings. This means heat is taken in, so evaporation and boiling are endothermic processes (ΔH +ve). If the temperature is high enough boiling takes place. Boiling is rapid evaporation anywhere in the bulk liquid and at a fixed temperature called the

boiling point and requires continuous addition of heat. The rate of boiling is limited by the rate of heat transfer into the liquid. * Evaporation takes place more slowly than boiling at any temperature between the melting point

and boiling point, and only from the surface, and results in the liquid becoming cooler due to loss of higher kinetic energy particles.

More details on the energy changes for these physical changes of state for a range of substances are dealt with in a section of the Energetic Notes.

Condensing (gas to liquid)

On cooling, gas particles lose kinetic energy and eventually become attracted together to form a liquid i.e. they haven't enough kinetic energy to remain free in the gaseous state.

There is an increase in order as the particles are much closer together and can form clumps of molecules.

The process requires heat to be lost to the surroundings i.e. heat given out, so condensation is exothermic (ΔH -ve).

o This is why steam has such a scalding effect, its not just hot, but you get extra heat transfer to your skin due to the exothermic condensation on your surface!

Distillation

Simple and fractional distillation involve the processes of boiling and condensation and are described on the Elements, Compounds and Mixtures Part 2 pages, where other methods of separation are also described.

The process of distillation involves boiling (liquid ==> gas/vapor) and the reverse process of condensation (gas/vapour ==> liquid)

Melting (solid to liquid)

When a solid is heated the particles vibrate more strongly as they gain kinetic energy and the particle attractive forces are weakened.

Eventually, at the melting point, the attractive forces are too weak to hold the particles in the structure together in an ordered way and so the solid melts.

o Note that the intermolecular forces are still there to hold the bulk liquid together - but the effect is not strong enough to form an ordered crystal lattice of a solid.

The particles become free to move around and lose their ordered arrangement. Energy is needed to overcome the attractive forces and give the particles increased kinetic

energy of vibration. So heat is taken in from the surroundings and melting is an endothermic process (ΔH +ve). Energy changes for these physical changes of state for a range of substances are dealt

with in a section of the Energetics Notes.

Freezing (liquid to solid)

On cooling, liquid particles lose kinetic energy and so can become more strongly attracted to each other.

When the temperature is low enough, the kinetic energy of the particles is insufficient to prevent the particle attractive forces causing a solid to form.

Eventually at the freezing point the forces of attraction are sufficient to remove any remaining freedom of movement (in terms of one place to another) and the particles come together to form the ordered solid arrangement (though the particles still have vibrational kinetic energy.

Since heat must be removed to the surroundings, so strange as it may seem, freezing is an exothermic process (ΔH -ve).

Cooling and Heating Curves and the comparative energy changes of state changes

gas Liquid solid

2f(i) Cooling curve: Note the temperature stays constant during the state changes of condensing at temperature Tc, and freezing/solidifying at temperature Tf. This is because all the heat energy removed on cooling at these temperatures (the latent heats or enthalpies of state change), allows the strengthening of the inter-particle forces without temperature fall (the heat loss is compensated by the exothermic increased intermolecular force attraction). In between the 'horizontal' state change sections of the graph, you can see the energy 'removal' reduces the kinetic energy of the particles, lowering the temperature of the substance.

A cooling curve summarizes the changes:

gas liquid s Solids

4.7 Identify the practical effects of expansion and contraction.e.g.railway lines,

Bridges, shrink fitting, bearing tolerances, steam pipes and bi metallic strip.

Thermal Expansion and Contraction with Examples

Thermal Expansion and Contraction

Most of the matters, without some exceptions, expand with the increasing temperature. When

you give heat to matters; speed of its particles increase and distance between them also

increase which results in the increase of the volumes of matters. All expansions occurs in

volume of the substance however, sometimes some of the dimensions of them expand more

with respect to others. In this case we neglect the less expanded ones and assume expansion

like linear expansion in long materials. Moreover, we take the expansion of plate as area

expansion and finally we take the expansion in three dimensions as

Inverse of the expansion is called contraction.

Volume expansion.

Expansion in Solid Matters

We will examine this subject under three title, linear expansion, area expansion and

volume expansion.

Linear Expansion: Picture given below shows the linear expansion of metal rod.

When it is heated, its length increases.

 

 

 

 

 

Our formula for linear expansion is;

∆L=L0.α. ∆T

Where; ∆L is the amount of change in the length of the rod, L0 is the initial length of the

road, α is the coefficient of linear expansion and ∆T is the change in the temperature

of the matter.

Area Expansion: When plate given below is heated, it expands in two dimensions

X and Y. We find the area expansion with the given formula;

∆S=S0.2α. ∆T

Where; ∆S is the amount of

change in the area of the

plate, S0 is the initial area of

the plate, 2α is the

coefficient of area

expansion and ∆T is the change in the temperature of the matter.

 

 

Example: We cut a circular piece from the rectangular plate. Which ones of the

processes given below can help us in passing through the circular piece from the

hole?

 

 

  

 

I. Increasing the temperatures of rectangular plate and circular piece

II. Decreasing the temperature of the circular piece

III. Decreasing the temperatures of the rectangular plate and circular piece

I. If we increase the temperatures of the plate and circular piece, expansion of

the hole and the circular piece will be the same. Thus, this option can help

us.

II. II. If we decrease the temperature of the circular piece, it contracts and hole

becomes larger than the piece. This option can also help us.

III. If we decrease the temperatures of the plate and circular piece, hole and circular

piece contract in same size. This process can also help us.

Volume Expansion:

If the objects expand in volume with the gained heat, we call this volume expansion

and find it with the following formula;

∆V=V0.3α. ∆T

Where; ∆V is the amount of change in the volume of the cube, V0 is the initial volume

of the cube, 3α is the coefficient of volume expansion and ∆T is the change in the

temperature of the matter.

 

 

 

 

 

 

Examples and ApplicationsFor applications using the thermal expansion property, see bi-metal and mercury-in-glass thermometer.

The expansion and contraction of materials must be considered when designing large structures, when using tape or chain to measure distances for land surveys, when designing molds for casting hot material, and in other engineering applications when large changes in dimension due to temperature are expected.

Thermal expansion is also used in mechanical applications to fit parts over one another, e.g. a bushing can be fitted over a shaft by making its inner diameter slightly smaller than the diameter of the shaft, then heating it until it fits over the shaft, and allowing it to cool after it has been pushed over the shaft, thus achieving a 'shrink fit'. Induction shrink fitting is a common industrial method to pre-heat metal components between 150 °C and 300 °C thereby causing them to expand and allow for the insertion or removal of another component.

There exist some alloys with a very small linear expansion coefficient, used in applications that demand very small changes in physical dimension over a range of temperatures. One of these is Invar 36, with α approximately equal to 0.6×10−6/°C. These alloys are useful in aerospace applications where wide temperature swings may occur.

Pullinger's apparatus is used to determine linear expansion of a metallic rod in laboratory. The apparatus consists of a metal cylinder closed at both ends (called a steam jacket). It is provided with an inlet and outlet for the steam. The steam for heating the rod is supplied by a boiler which is connected by a rubber tube to the inlet. The center of cylinder contains a hole to insert a thermometer. The rod, under investigation, is enclosed in a steam jacket. Its one end is free, but the second end is pressed against a fixed screw. The position of the rod is determined by a micrometer screw gauge or spherometer.

The control of thermal expansion in ceramics is a key concern for a wide range of reasons. For example, ceramics are brittle and cannot tolerate sudden changes in temperature (without cracking) if their expansion is too high. Ceramics need to be joined or work in consort with a wide range of materials and therefore their expansion must be matched to the application. Because glazes need to be firmly attached to the underlying porcelain (or other body type) their thermal expansion must be tuned to 'fit' the body so that crazing or shivering do not occur. Good example of products whose thermal expansion is the key to their success are Corning Ware and the spark plug. The thermal expansion of ceramic bodies can be controlled by firing to create crystalline species that will influence the overall expansion of the material in the desired direction. In addition or instead the formulation of the body can employ materials delivering particles of the desired expansion to the matrix. The thermal expansion of glazes is controlled by their ceramic chemistry. In most cases there are complex issues involved in controlling body and glaze expansion, adjusting for thermal expansion must be done with an eye to other properties that will be affected, generally trade-offs are required.

Heat-induced expansion has to be taken into account in most areas of engineering. A few examples are:

Metal framed windows need rubber spacers Rubber tires Metal hot water heating pipes should not be used in long straight lengths Large structures such as railways and bridges need expansion joints in the

structures to avoid sun kink One of the reasons for the poor performance of cold car engines is that parts have

inefficiently large spacing until the normal operating temperature is achieved. A gridiron pendulum uses an arrangement of different metals to maintain a more

temperature stable pendulum length. A power line on a hot day is droopy, but on a cold day it is tight. This is because the metals

expand under heat.

Thermometers are another application of thermal expansion — most contain a liquid (usually mercury or alcohol) which is constrained to flow in only one direction (along the tube) due to changes in volume brought about by changes in temperature. A bi-metal mechanical thermometer uses a bimetallic strip and registers changes due to the differing coefficient of thermal expansion between the two materials.

4.8 Explain the term specific heat capacity and state the SI derived units.

Specific Heat CapacityThe specific heat capacity of a solid or liquid is defined as the heat required raising unit mass of substance by one degree of temperature. This can be stated by the following equation:

Where,

Q = Heat supplied to substance, m = Mass of the substance, c = Specific heat capacity,

T = Temperature rise.

There are two definitions for vapors and gases: Cp = Specific heat capacity at constant pressure, i.e.

Cv = Specific heat capacity at constant volume, i.e.

It can be shown that for a: perfect gases.

Where, R is the gas constant.

The ratio, Cp/Cv, has been given symbol ,

and is always greater than unity. The approximate value of this ratio is 1.6 for monatomic gases such as Ar and He. Diatomic gases (such as H2, N2, CO and O2) have a g ratio about 1.4 and tri atomics (such as SO2 and CO2) 1.3.

Converting between Common Units

1 Btu/lbmoF = 4186.8 J/kg K = 1 kcal/kgoC

Specific Heat Capacity Gases

There are two definitions of Specific Heat Capacity for vapors and gases:

cp = (δh/δT)p - Specific Heat Capacity at constant pressure (kJ/kgoC)

cv = ( δh/ δT)v - Specific Heat Capacity at constant volume (kJ/kgoC)

Gas Constant

The gas constant can be expressed as

R = cp - cv         (2)

Where

R = Gas Constant

4.9 Explain the principle of Latent heat when a change of state occurs (From ice to

Water and water to steam).

Latent Heat

Latent Heat is the energy needed to change a substance to a higher state of matter. This same energy is released from the substance when the change of state (or phase) is reversed. The diagram below describes the various exchanges of heat involved with 1 gram of water.

Figure : Latent heat exchanges of energy involved with the phase changes of water. 

Figures 6c-2 and 6c-3 show the net absorption and release of latent heat energy for the Earth's surface for January and July, respectively. The highest values of flux or flow occur near the subtropical oceans where high temperatures and a plentiful supply of water encourage the evaporation of water. Negative values of latent heat flux indicate a net release of latent energy back into the environment because of the condensation or freezing of water. Values of latent heat flux are generally low over landmasses because of a limited supply of water at the ground surface

.

Figure : Mean January latent heat flux for the Earth's surface, 1959-1997. (Source of Original Modified Image: Climate Lab Section of the Environmental Change Research Group, Department of Geography, University of Oregon - Global Climate Animations).

 

4.10 Identify the effects of friction (Resistance to motion, heat generation).

Introduction

Friction is a force between objects that opposes the relative motion of the objects. In this project, you will be studying kinetic friction (also called sliding friction). When two objects are moving relative to one another, kinetic friction converts some of the kinetic energy of that motion into heat. You can feel the heat of kinetic friction if you rub your hands together.

The same thing happens when two objects are sliding past one another—for example, when you push a box across the floor. Part of the energy of your pushing moves the box, and part of the energy is lost to kinetic friction. How much energy is lost? What factors do you think will act to increase or decrease kinetic friction?

Think about what happens if you rub your hands together. If you press your hands together, you have to push harder to slide your hands past each other, and your hands heat up more quickly. Pressing your hands together is like adding more weight to the box before trying to slide it across the floor. The added weight makes the box push down harder on the floor, and you will have to push harder on the box to make it slide.

Think about what happens if you rub your hands against a smooth, polished surface, like wood furniture, compared to a surface with a rougher texture, like denim cloth. Which surface produces more kinetic friction?

The goal of this project is to investigate how the texture of surfaces affects the amount of kinetic friction produced when objects move across different test surfaces.

Terms, Concepts and Questions to Start Background Research

To do this project, you should do research that enables you to understand the following terms and concepts:

kinetic (sliding) friction, Forces.

More advanced students should also study: Newton’s laws of motion, normal force, Coefficient of friction.

Measuring Friction

Measures of friction are based on the type of materials that are in contact. Concrete on concrete has a very high coefficient of friction. That coefficient is a measure of how easily one objects moves in relationship to another. When you have a high coefficient of friction, you have a lot of friction between the materials. Concrete on concrete has a very high coefficient, and Teflon on most things has a very low coefficient. Teflon is used on surfaces where we don't want things to stick; such as pots and pans.

Scientists have discovered that there is even less friction in your joints than in Teflon! It is one more example at how efficient living organisms can be.

Questions

How is friction produced? What effect does friction have on the speed of a rolling object? What types of surfaces will produce the most friction when they rub against one another? What

types of surfaces will produce the least amount of friction? When you want to go down a slide at the playground, you first have to climb up a ladder,

working against gravity to get to the top. When you slide down, only part of the energy of your climb goes into the speed of your slide. What happens to the rest of the energy of your climb?

Variations

What happens if you hold the test surface and the object constant, but change the weight of the object (by attaching progressively more weight on top of the object)? Make a graph of distance traveled vs. object weight under these conditions.

Use a spring scale to measure the force needed to drag various objects across different surfaces. Record both the transient force needed to overcome static friction (Figure 1, left), and the maintained force necessary to counteract sliding friction (Figure 1, right). How do these two forces vary with different surfaces? How do these forces vary with the weight (normal force) of the test object? How do these forces vary with the surface area of the test object?

Figure 1. Using a spring scale to measure static friction (top) and sliding friction (bottom) of an object.

Resistance to motion by friction

Heat Generation by friction

Space Shuttle at re-entry

S540/772 Rights Managed

Caption: Space shuttle re-entry. Artwork of the space shuttle glowing during re-entry. The space shuttle is covered in heat resistant tiles made from silica. These protect it from heat generated by friction as it enters the atmosphere at high speed. The glow is due to the tiles being heated until they are white hot (seen at the nose at upper right).

4.11 Identify applications where the frictions forces are advantage and

Disadvantage.

ADVANTAGES OF FRICTION

In some situations, friction is very important and beneficial. There are many things that you could not do without the force of friction.

WalkingYou could not walk without the friction between your shoes and the ground. As you try to step forward, you push your foot backward. Friction holds your shoe to the ground, allowing you to walk.

WritingWriting with a pencil requires friction. You could not hold a pencil in your hand without friction. It would slip out when you tried to hold it to write. A pencil eraser uses friction to rub off mistakes written in pencil lead. Rubbing the eraser on the lead wears out the eraser due to friction, while the particles worn off gather up the pencil lead from the paper.

Driving carYour car would not start moving if it wasn't for the friction of the tires against the street. With no friction, the tires would just spin. Likewise, you could not stop without the friction of the brakes

and the tires.

DISADVANTAGES OF FRICTION

Friction can cause problems or be a nuisance that you try to minimize.

Makes movement difficult

Any time you want to move an object, friction can make the job more difficult. Excess friction can make it difficult to slide a box across the floor, ride a bicycle or walk through deep snow. An automobile would not move forward very well unless its friction was not reduced. Oil is needed to lubricate the engine and allow its parts to move easily. Oil and ball bearings are also used in the wheels, so they will turn with little friction.

Wastes energy

In any type of vehicles as a car, boat or airplane--excess friction means that extra fuel must be used to power the vehicle. In other words, fuel or energy is being wasted because of the friction. Fluid friction or air resistance can greatly reduce the gas mileage in an automobile.

Heats parts

The Law of Conservation of Energy states that the amount of energy remains constant. Thus, the energy that is "lost" to friction in trying to move an object is really turned to heat energy. You've seen how people will try to start a fire by vigorously rubbing two sticks together. Or perhaps you've seen an automobile spin its wheels so much that the tires start to smoke. These are examples of friction creating heat energy. Just rub your hands together to create the same effect. Besides the problem of losing energy to heat, there is also the threat of a part overheating due to friction. This can cause damage to a machine.

Wears things out

Any device that has moving parts can wear out rapidly due to friction. Lubrication is used not only to allow parts to move easier but also to prevent them from wearing out. Some other examples of materials wearing out due to friction include the soles of your shoes and a pencil eraser.

CompromiseA compromise is needed between much friction and not enough. For example, if you wanted to slide a heavy box across the floor, you would want to reduce the friction between the box and the floor, so that it would be easy to move. Lubrication of some sort is often a way to reduce friction.

In conclusion

Friction is necessary in many applications to prevent slipping or sliding. But also, it can be a nuisance because it can hinder motion. A good compromise is necessary to get just enough friction or a proper combination of frictions.

METHODS OF REDUCING FRICTIONThere are a number of methods to reduce friction in which some are discussed here.Use of lubricants:The parts of machines which are moving over one another must be properly lubricated by using oils and lubricants of suitable viscosity.

Use of grease:Proper greasing between the sliding parts of machine reduces the friction.

Use of ball bearing:In machines where possible, sliding friction can be replaced by rolling friction by using ball bearings.

Design modification:Friction can be reduced by changing the design of fast moving objects. The front of vehicles and airplanes made oblong to minimize friction.    

4.12 Explain how lubricant can be used to reduce the friction.

lubricant

A lubricant (sometimes referred to as "lube") is a substance (often a liquid) introduced between two moving surfaces to reduce the friction between them, improving efficiency and reducing wear. It may also have the function of dissolving or transporting foreign particles and of distributing heat. A lubricant's ability to lubricate moving parts and reduce friction is the property known as lubricity.

One of the single largest applications for lubricants, in the form of motor oil, is protecting the internal combustion engines in motor vehicles and powered equipment.

Description

Typically lubricants contain 90% base oil (most often petroleum fractions, called mineral oils) and less than 10% additives. Vegetable oils or synthetic liquids such as hydrogenated polyolefin, esters, silicones, fluorocarbons and many others are sometimes used as base oils. Additives deliver reduced friction and wear, increased viscosity, improved viscosity index, resistance to corrosion and oxidation, aging or contamination, etc.

Lubricants such as 2-cycle oil are added to fuels like gasoline which has low lubricity. Sulfur impurities in fuels also provide some lubrication properties, which have to be taken in account when switching to a low-sulfur diesel; biodiesel is a popular diesel fuel additive providing additional lubricity.

Non-liquid lubricants include grease, powders (dry graphite, PTFE, Molybdenum disulfide, tungsten disulfide, etc.), Teflon tape used in plumbing, air cushion and others. Dry lubricants such as graphite, molybdenum disulfide and tungsten disulfide also offer lubrication at temperatures (up to 350 °C) higher than liquid and oil-based lubricants are able to operate. Limited interest has been shown in low friction properties of compacted oxide glaze layers formed at several hundred degrees Celsius in metallic sliding systems, however, practical use is still many years away due to their physically unstable nature.

Another approach to reducing friction and wear is to use bearings such as ball bearings, roller bearings or air bearings, which in turn require internal lubrication themselves, or to use sound, in the case of acoustic lubrication.

In addition to industrial applications, lubricants are used for many other purposes. Other uses include cooking (oils and fats in use in frying pans, in baking to prevent food sticking), bio-medical applications on humans (e.g. lubricants for artificial joints), ultrasound examination, internal examinations for males and females, and the use of personal lubricant for sexual purposes.

Purpose

Lubricants perform the following key functions.

Keep moving parts apart Reduce friction Transfer heat Carry away contaminants & debris Transmit power Protect against wear Prevent corrosion Seal for gases

Stop the risk of smoke and fire of objects

Keep moving parts apart

Lubricants are typically used to separate moving parts in a system. This has the benefit of reducing friction and surface fatigue together with reduced heat generation, operating noise and vibrations. Lubricants achieve this by several ways. The most common is by forming a physical barrier i.e. a thin layer of lubricant separates the moving parts. This is termed hydrodynamic lubrication. In cases of high surface pressures or temperatures the fluid film is much thinner and some of the forces are transmitted between the surfaces through

Reduce friction

Typically the lubricant-to-surface friction is much less than surface-to-surface friction in a system without any lubrication. Thus use of a lubricant reduces the overall system friction. Reduced friction has the benefit of reducing heat generation and reduced formation of wear particles as well as improved efficiency. Lubricants may contain additives known as friction modifiers that chemically bind to metal surfaces to reduce surface friction even when there is insufficient bulk lubricant present for hydrodynamic lubrication, e.g. protecting the valve train in a car engine at startup.

Transfer heat

Both gas and liquid lubricants can transfer heat. However, liquid lubricants are much more effective on account of their high specific heat capacity. Typically the liquid lubricant is constantly circulated to and from a cooler part of the system, although lubricants may be used to warm as well as to cool when a regulated temperature is

required. This circulating flow also determines the amount of heat that is carried away in any given unit of time. High flow systems can carry away a lot of heat and have the additional benefit of reducing the thermal stress on the lubricant. Thus lower cost liquid lubricants may be used. The primary drawback is that high flows typically require larger sumps and bigger cooling units. A secondary drawback is that a high flow system that relies on the flow rate to protect the lubricant from thermal stress is susceptible to catastrophic failure during sudden system shut downs. An automotive oil-cooled turbocharger is a typical example. Turbochargers get red hot during operation and the oil that is cooling them only survives as its residence time in the system is very short i.e. high flow rate. If the system is shut down suddenly (pulling into a service area after a high speed drive and stopping the engine) the oil that is in the turbo charger immediately oxidizes and will clog the oil ways with deposits. Over time these deposits can completely block the oil ways, reducing the cooling with the result that the turbo charger experiences total failure typically with seized bearings. Non-flowing lubricants such as greases & pastes are not effective at heat transfer although they do contribute by reducing the generation of heat in the first place.

Carry away contaminants and debris

Lubricant circulation systems have the benefit of carrying away internally generated debris and external contaminants that get introduced into the system to a filter where they can be removed. Lubricants for machines that regularly generate debris or contaminants such as automotive engines typically contain detergent and dispersant additives to assist in debris and contaminant transport to the filter and removal. Over time the filter will get clogged and require cleaning or replacement, hence the recommendation to change a car's oil filter at the same time as changing the oil. In closed systems such as gear boxes the filter may be supplemented by a magnet to attract any iron fines that get created.

It is apparent that in a circulatory system the oil will only be as clean as the filter can make it, thus it is unfortunate that there are no industry standards by which consumers can readily assess the filtering ability of various automotive filters. Poor filtration significantly reduces the life of the machine (engine) as well as making the system inefficient.

Transmit power

Lubricants known as hydraulic fluid are used as the working fluid in hydrostatic power transmission. Hydraulic fluids comprise a large portion of all lubricants produced in the world. The automatic transmission's torque converter is another important application for power transmission with lubricants.

Protect against wear

Lubricants prevent wear by keeping the moving parts apart. Lubricants may also contain anti-wear or extreme pressure additives to boost their performance against wear and fatigue.

Prevent corrosion

Good quality lubricants are typically formulated with additives that form chemical bonds with surfaces to prevent corrosion and rust.

Seal for gases

Lubricants will occupy the clearance between moving parts through the capillary force, thus sealing the clearance. This effect can be used to seal pistons and shafts.

Types of lubricantsIn 1999, an estimated 37,300,000 tons of lubricants were consumed worldwide.The majority was for automobiles, but other industrial, marine, and metal work applications are also big consumers of lubricants. Although air and other gas-based lubricants are known, e.g. in fluid bearings), liquid and solid lubricants dominate the market, especially the former.

Lubricants are generally composed of a majority of base oil and a minority of additives to impart desirable characteristics. Although generally lubricants are based on one type of base oil or another, it is quite possible to use mixtures of the base oils to meet performance requirements.

Base oil groups

Mineral oil term is used to encompass lubricating base oil derived from crude oil. The American Petroleum Institute (API) designates several types of lubricant base oil identified as:

Group I – Saturates <90% and/or sulfur >0.03%, and Society of Automotive Engineers (SAE) viscosity index (VI) of 80 to 120

Manufactured by solvent extraction, solvent or catalytic dewaxing, and hydro-finishing processes. Common Group I base oil are 150SN (solvent neutral), 500SN, and 150BS (bright stock)

Group II – Saturates over 90% and sulfur under 0.03%, and SAE viscosity index of 80 to 120

Manufactured by hydro cracking and solvent or catalytic dewaxing processes. Group II base oil has superior anti-oxidation properties since virtually all hydrocarbon molecules are saturated. It has water-white color.

Group III – Saturates > 90%, sulfur <0.03%, and SAE viscosity index over 120

Manufactured by special processes such as isohydromerization. Can be manufactured from base oil or slax wax from dewaxing process.

Group IV – Polyalphaolefins (PAO) Group V – All others not included above

Such as naphthenic, PAG, esters, etc.

In North America, Groups III, IV and V are now described as synthetic lubricants, with group III frequently described as synthesized hydrocarbons, or SHCs. In Europe, only Groups IV and V may be classed as synthetics.

The lubricant industry commonly extends this group terminology to include:

Group I+ with a Viscosity Index of 103–108 Group II+ with a Viscosity Index of 113–119 Group III+ with a Viscosity Index of at least 140

Can also be classified into three categories depending on the prevailing compositions:

Paraffinic Naphthenic Aromatic

While lubricants for use in internal combustion engines may solely consist of one of the above-mentioned oil groups, it is not desirable in practice. Additives to reduce oxidation and improve lubrication are added to the final product. The main constituent of such lubricant product is called the base oil, base stock. While it is advantageous to have a high-grade base oil in a lubricant, proper selection of the lubricant additives is equally as important. Thus some poorly selected formulation of PAO lubricant may not last as long as more expensive formulation of Group III+ lubricant.

These are primarily triglyceride esters derived from plants and animals. For lubricant base oil use the vegetable derived materials are preferred. Common ones include high oleic canola oil, castor oil, palm oil, sunflower seed oil and rapeseed oil from vegetable,

and Tall oil from animal sources. Many vegetable oils are often hydrolyzed to yield the acids which are subsequently combined selectively to form specialist synthetic esters. Other naturally derived lubricants include lanolin (wool grease, a natural water repellent).

Whale oil was a historically important lubricant, with some uses up to the latter part of the 20th century as a friction modifier additive for automatic transmission fluid.[3]

In 2008, the biolubricant market was around 1% of UK lubricant sales in a total lubricant market of 840,000 tones/year.

Lanolin is a natural water repellent, derived from sheep wool grease, and is an alternative to the more common petro-chemical based lubricants. This lubricant is also a corrosion inhibitor, protecting against rust, salts, and acids.

Water can also be used on its own or as a major component in combination with one of the other base oils. Commonly used in engineering processes, such as milling and lathe turning.

Synthetic oils

Polyalpha-olefin (PAO) Synthetic esters Polyalkylene glycols (PAG) Phosphate esters Alkylated naphthalenes (AN) Silicate esters Ionic fluids

Solid lubricants

Teflon or PTFE: Teflon (PTFE) is typically used as a coating layer on, for example, cooking utensils to provide a non-stick surface. Its usable temperature range up to 350°C and chemical inertness make it a useful additive in special greases. Under extreme pressures, Teflon powder or solids is of little value as it is soft and flows away from the area of contact. Ceramic or metal or alloy lubricants must be used then.

Inorganic solids: Graphite, hexagonal boron nitride, molybdenum disulfide and tungsten disulfide are examples of materials that can be used as solid lubricants, often to very high temperature. The use of some such materials is sometimes restricted by their poor resistance to oxidation (e.g., molybdenum disulfide can only be used up to 350°C in air, but 1100°C in reducing environments).

Metal/alloy: Metal alloys, composites and pure metals can be used as grease additives or the sole constituents of sliding surfaces and bearings. Cadmium and Gold are used for plating surfaces which gives them good corrosion resistance and sliding properties, Lead, Tin, Zinc alloys and various Bronze alloys are used as sliding bearings, or their powder can be used to lubricate sliding surfaces alone, or as additives to greases.

AdditivesA large number of additives are used to impart performance characteristics to the lubricants. The main families of additives are:

Antioxidants Detergents Anti-wear Metal deactivators Corrosion inhibitors , Rust inhibitors Friction modifiers Extreme Pressure Anti-foaming agents Viscosity index improvers Demulsifying/Emulsifying Stickiness improver, provide adhesive property towards tool surface (in

metalworking)

Complexing agent (in case of greases)

4.13 Describe force as a vector quantity.

FORCE

Force is a vector quantity. It has both magnitude and direction. Let's look at a something and think about it. If you apply a force to something in an attempt to move it, the force will have to have direction associated with its magnitude. It must have direction. It doesn't make sense for force to not have direction. Gravity is a force of attraction between masses.

Scalars have radial direction with the origin, so force can be a scalar or a vector.

A ball falls because the Force like many quantities in Physics is a quaternion. A quaternion consists of a scalar and a vector, so force can be a scalar or and vector. Scalars can be said to have direction.

A unit quaternion Force F = (cos(angle) + v sin(angle)) if the angle is a even multiple of 90 degrees, the quaternion force is a scalar; if the angle is an odd multiple of 90 degrees, the Quaternion Force is a vector. It is the angle that determines whether the force is a scalar or a vector. You could say that scalars and vectors both have directions (angles) and it is the value of the angel that determines a scalar or a vector. If the angle is not a multiple of 90 degrees, force is both a scalar and a vector.

For example:

F= qvB = -qv.B + qvxB = qvB (cos (vB) +v sin (vB)).

In general the Lorentz Forces is

Fv =qvxB

but there is a scalar force : Fs = -qv.B that is ignored or denied.

Gravitation has a scalar force the real derivative of the gravitational Potential Energy.

F= d/dr Ep = d/dr -mu/r = mu/r2,

The centripetal force of attraction to the center of gravity. The scalar force has a direction radial to or from the center of gravity.