MODULE THERMODYNAMICS1-4

Colorado State University

I. HEAT AND TEMPERATUREExamples from nature hot and coldConcept of heat Concept of temperature Measurements of temperatureII. WAYS OF ENERGY TRANSFER BY HEAT Conductors and insulatorsConvectionRadiationModel explanationIII. THERMAL EXPANSIONExamples from everyday life Experiment with metal expansionDependence on temperature mathematical descriptionIV. STATES OF MATTERGases, liquids, solid states structureChange of states General scheme of states of matter changes

HEAT AND TEMPERATUREWhat does it mean cold?Why you fell that glass with tea is hot?Why the snow is cold?1. Examples from nature hot and cold Lets make a simple experiment

First put your left hand to the water with ice and right to the hot water, wait a half a minute, then put two hands together to a warm water.What are you feeling now? Do you know why?

HOT BODY

COLD BODY

transfer of energy by heat 2. Concept of heat

Heat is a process of energy transfer between bodies of different temperature.

Energy transfer is taking place during the collision of body molecules

Examples: Transfer of energy by heat from oven to air in the room and from air to all elements in the room.Transfer of energy by heat from the gas burner to the kettle and next to the water inside the kettle.Can you give more examples?

3.Concept of temperature Lets see how molecules are moving and make collisions between themselveson the 2 dimensional air table (use the video movie).

Lets see now the simulation of molecules motion in 3 dimensional model (use the video movie)Particles are moving in the box, all in the random directions.They transfer energy during collisions between themselves and between them and the walls.

Temperature depends on particles speed:T ~ particles speedIf temperature increases, the speed of molecules increases too, if temperature decreases the speed decreases too. As the result we can define the temperature:Temperature is a physical quantity characterising the kinetic energy of linear motion of molecules.Temperature scales Kelvin, Celsius and Fahrenheit

The first mercury thermometer was constructed by Gabriel Fahrenheit in Gdansk in 1720.

Zero point was connected with the lowest winter air temperature(approximately -17 C) and 100 F was connected to the body temperature of Fahrenheits wife.

For Kelvin scale 0 is absolute value which presents the lowest temperature in nature then particles are not moving are at rest. 273 K is a temperature of the freezing water.

The Celsius scale, most popular in Europe, is connected to the freezing (0 C ) and boiling (100 C) points of water.

The formula for units conversion is as follows:

Temperature conversion Java Applet

Measurements of cold and warm water temperatureLets prepare two glasses first one with warm water and the second one with the ice. Please measure the temperature using ordinary thermometers and electronic temperature detector.

2. WAYS OF ENERGY TRANSFER BY HEAT 1. We can recognize three main different ways of thermal energy transfer (by heat): conduction, convection, radiation.2. Experiment concerned with heating of wood and copperPlease prepare the candle, two pieces of paper and wood and metal cylinders. Make experiment (or see the video film) and answer the question: which cylinder is heat conductor and which is heat isolator?After the process of heating the paper with wood cylinder is more dark than the paper with copper cylinder. It means that metal is a good heat CONDUCTOR but wood is an ISOLATOR

Conductors and insulatorsWhy the teaspoon in the hot cup of tea is hot?How the air in the room is hot when warm oven is there?

3. Thermal properties of different materialsThe figure below shows an experiment presenting the thermal properties of different materials. There is a series of rods made from different materials and covered by wax. Their ends are placed in hot water. What we observe?We can notice that wax is melting first on the copper and aluminium rods and lastly on plastic and glass rods. The reason is some materials are good heat conductors but some good heat isolators

Convection2.1. Convection in glass pipe

Please heat the water in the closed glass pipe and observe the behaviour of cork pieces in water (make experiment or see the video film).

We can see that when one part of fluid or gas is hotter than another part, the hot part tends to move upwards. We are dealing with the convection process.Convection is a process of thermal energy transfer (by heat). As the result convection currents circulate around the fluid or gas.

2.2. Convection of hot and cold air in the roomThere is the scheme of air circulation in the room as a result of convection currents.

RadiationThe process of radiation transfers thermal energy in the form of heat even there is no connection between source of heat and the receiver. For example, heat energy from the Sun reaches us as radiation, because it is transported through open space.Please notice that there is no connection between cup and books shown in the picture below, but after a while cold books will be hotter.Heat energy will be transferredbetween hot cup to cold books by radiation which we called infra-red radiation. We can not see it, but we can feel it on our skin because it raises its temperature.

Thermal camera* can make the picture of infrared radiation of different bodies as for example human body (see picture on the left side). In this picture the red and bright places indicate hot parts of human body, but dark places- cold parts. Please notice that the hottest place of human body is the head.This camera can be also used during the night. When your eyes didnt see anything camera detect all radiating objects, as for example: peoples, animals and machines.The name of this special camera is noctovisor.* Extended content

4. Model explanation*HOT

COLD

The energy transfer by heat is going always from hot to cold materials

The molecules with higher energy (higher velocity and mass) transfer it to the molecules with the lower energy.This process is taking place in a gases, liquids and solids.In a gases and liquids transfer of energy occurring during collisions.In solids vibrating atoms in one part of material pass on their vibrations to atoms close to them.

THERMAL EXPANSION Examples from everyday life Lets see how bridge is constructed. It contains expansion joints (see picture below). Why? Whats going on with metals when they are hot or cold?

The bridges must be constructed with the use of expansion joints to allow the thermal expansion, otherwise they might buckle.

There are expansion jointsin the railroadsPlease observe the construction of railroads (picture below).

What we see at the electrical traction wires?

The electric wires are hanging down here, because it was a sunny day when the photo was taken. But during the winter time temperature is falling down and the wires start contract. They use the extra piece of sunny wire, so they will not brake off.When is hot metals are expanding. When is cold - they contracting.

Experiment with metal expansion Lets see experiment presenting expansion of metal piece in a special device (make experiments or see the video film).

When we heat the device the metal arm is expanding. We correct its length by using screw. When we stop heating we put a cold piece of fabric on a metal arm and observe that metal arm starts contracting as it broke piece of glass.

Dependence on temperature mathematical description Lets tray to calculate how big expansion is when we heat a piece of metal.

The starting situation is as follows. The piece of metal have length L1 and temperature T1:

When we heat the piece of metal, temperature increases and the metal expands.The new length is L2 at temperature T2.The change of temperature: T = T2 T1The change of length: L = L2 L1For temperature change T the mathematical formula describing the length change L, is:L = L T where is linear coefficient of thermal expansion. It is different for different materials.Calculation exerciseFind the change in the total length of the 2700 m long Golden Gate Bridge, as the temperature increased from 5 C in the morning to 25 OC at the noon. The bridge is constructed with steel.SolutionIn the table we can find that steel have a coefficient of thermal expansion 1.2*10-5 1/C.Lets apply equation:L = L TT = 25 OC 5 OC = 20 CthenL = L T = 1,2 *10-5 1/C * 2700 m * 20 OC = 0,65 m = 65 cmThats a reason that expansion joints are very necessary!

Solids [1/oC]Copper1.7 *10-5Aluminium2.4 *10-5Gold1.4 *10-5Steel1.2 *10-5

STATES OF MATTERGases, liquids and solid states Examples from natureWhat does it mean states of matter?What kind of matter do you see in the pictures below?

You can recognize three different state of matter: gas vapour of the water in the kettle,liquid tap water,solid state icicle behind the window.

Model of states of matterHere you see how molecules are packed in different states (solid state, liquid and gas).

In the solid states molecules are packed very tightly.In liquids molecules have some space between themselves. And in gases molecules are moving freely.

Solid state Liquid Gas

Change of states All substances can change their states and it depends on temperature.Lets see the pictures below showing the model of changing state of gas: In picture a the temperature is rather high, so atoms moving quickly and make collisions between themselves. In picture b and c we start decreasing temperature and atoms start moving more slowly and during the collisions they stick together, first to small groups and later to the bigger clusters.In picture d we can see that all molecules are grouped. There is very low temperature and gas is changing state to the liquid.The process when gas turns into liquid is called condensation.

General scheme of states of matter changes

For 3 states of matter there are 6 possible ways of their change. All of them are described in the below scheme:

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