4.3 understand that energy is conserved Energy cannot be destroyed norcreated; it is conserved.

The law of conservation of energy states that

in an isolated system, the total energy cannot

change – it cannot be destroyed nor created.

However, energy can change forms. In otherwords, it just means that energy can betransferred from different types of energy,for example electrical energy to kinetic energyor gravitational potential energy to thermal

and sound energy.An example of this is in the diagram below. The ball on the top has 1000J of GPEenergy and 0J of KE. Can you figure out what the KE of the ball is in the exactmoment before it hits the ground? It is actually fairly simple. The GPE energy istransferred into KE, so the KE is 1000J. This proves that energy is transferred andconserved but not destroyed.

4.6 Describe how energy transfer may take place by conduction, convection and radiationBy Kessandra and Olivia :3

Heat can be transferred in 3 ways: conduction, convection and radiation.

ConductionEverything is made up of particles that vibrateconstantly. When something is heated, theparticles near the hotter area vibrate faster. As aresult, the faster moving particles collide with theslower moving particles causing the heat energy tobe transferred to the slower moving particles. As aresult, the slower moving particles begin thevibrate faster. This process continues and heatenergy transfers to other areas. This process isknown as conduction.

Conduction can only happen in solids, liquids or gases and cannot occur in vacuums such as space.Metals are good conductors of heat and non-metals and gases are usually good insulators.

ConvectionWhen a fluid is heated, the part near the heatedarea has a higher temperature. As a result, thatarea becomes less dense and the particles in theheated area rises. The particles in the cooler areasinks to the bottom. The new, cooler particles alsogain energy and as a result, they rise too. Thehotter particles at the top have cooled down andsinks back down under the force of gravity. Theprocess repeats itself. This process is known asconvection and the cycle is known as a convectioncurrent.

Convection can only happen in liquids or gases (fluids) and cannot occur in vacuums and solids.

RadiationEnergy transferred by radiation is known as thetransfer of energy through electromagnetic waves.When an object absorbs the electromagnetic wave,the energy carried by the waves transfers to theparticles in the object. As a result, the object’stemperature rises.

Radiation can happen in vacuums, like space, whichis how Earth gets its heat from the Sun.

Lesson aims – To understand activities of convection in everyday life

4.7 – Role of convection

Convection occurs in everyday life. Whenyou boil water heat convects to the airaround us. Air and liquids convect. Hotteratoms become less dense and go up whilecooler ones sink down.

You sometimes turn on theair-conditioner in summer. Convectionoccurs when hot air rises as it vibratesmore and becomes less dense and allowsless dense air to sink.Fireplaces seem to heat the house byconvection but were proven wrong. Hotair rises and the heat from the smoke issucked up from the chimney. Sometimes,you feel that your back is cool when yousit in front of a fireplace – the air is suckedin by the fireplace. The only effectivemethod that fires heat you is radiation!

When you boil water and measure thetemperature of the container, the lowersection of it is often a few degrees lowerthan on the upper half of the container.This is because convection flows andforces hot water (less dense) to rise.

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4.8 explain how insulation is used to reduce energy transfers from buildings andthe human body.By: Joyce Chung

Insulation

Because air is a bad conductor of heat, insulators in buildingsusually contain pockets of trapped air to stop heat from beingconducted away. The wall cavities of these structures are usuallyfilled with an insulator such as polystyrene foam (it is sometimesalso coated with silver material to reflect infra-red radiation), andcarpets can be used to trap heat. Windows can also reduce energytransfers from buildings if they are double glazed. This is as theyhave a gap in which trapped air is held, so they reduce thermal

energy transfer through them.

On the other hand, the humanbody manages to reduce thermal energy transfer through thewearing of clothes. If they are made out of wool, it is particularlyeffective as it is made out of tiny fibres that trap heat betweenthem. The skin also manages to insulate heat through the raisingof hair follicles, although this may not be as useful.Because conduction is being reduced by poor conducting materialand radiation in buildings are being stopped by things reflectingheat, these methods are successful as convection is not a problemin a solid structure. The human body also has similar principles.

4.10 understand that work done is equal to energy transferred

Work done is equal to the energytransferred The work done is equal to energy transferred as seen in the Equation for power:

POWER = ENERGY TRANSFERRED/TIME

or WORK DONE/TIME

For example, when you walk up the stairs, If your Work done (FxD) is

40J then the energy transferred is also 40 J. This is because on earth, energy

cannot be destroyed or created, it can onlytransferred into a different form of energy.

Gravitational potential energy (4.11 - know and use the relationship :

GPE = mgh)

Gravitational potential energy is a type of stored energy. It is the energy a certain mass has

gained. The three factors that affect it is the mass and height of the object, as well as the

gravitational field strength (On Earth its 10).

If an object is raised above the ground, it gains gravitational potential energy. Remember, GPE

is always given in Joules as it is a form of energy.

To calculate GPE:

Change in GPE (joules) = Mass (kg) x Gravitational Field Strength (N/kg) x Height (m)

GPE = mgh

Example:

On Earth, a ball of 0.5kg is kicked straight up. How much GPE does it have

at its highest point 6m of the ground?

Answer:

The ball has a mass of 0.5kg, the maximum height is 6m and the

gravitational field strength is 10 (On Earth).

GPE = 0.5 * 6 * 10

= 12 joules

By: Aaryam Srivastava

4.12 know and use the relationship:

kinetic energy = 1/2 × mass × speed2

Kinetic EnergyKinetic energy is a type of energy which is stored in an object. A classic example

of this is an object which is rolling with speed. If an object has a mass and is

rolling in speed and we can calculate the kinetic energy of that object by the

following formula:

KE=½mv2

From this formula, we can figure out the relationship between mass, velocity and

kinetic energy. It goes as thus:

If v goes up by x number of times, then the KE (kinetic energy) will go up by 4x.

Example:

A ball is rolling on the ground at 20m/s. It has a mass of 100kg. Find it’s kinetic

energy.

KE=½mv2

KE=½ x 100 x 202

KE= 20000J

Extension:

GPE at start= KE at end

ONLY IF THE FOLLOWING IDEAS ARE TRUE:

1. Energy is conserved

2. Air resistance is negligible

Example:

A ball is falling towards the table and at the start it has a GPE of 10J. When the

ball is 1 atom spaced away from the table, its GPE is going to be 0J, and all the

energy is transferred into KE.

This also means that:

GPE top= KE bot

½mv2=mgh

½v2=gh

v2=2gh

v=(2gh)1/2

4.13 Understand how conservation of energy produces a link

between gravitational potential energy, kinetic energy and

work

Link between GPE, KE and work – Justin YimGPE, as you can see from the diagram, is

mass x gravitational field strength x

height. KE, is ½ x mass x velocity

squared. Another important thing to

remember is the law conservation of

energy which states “energy cannot be

created of destroyed, it just changes

forms”. There is a link between

gravitational potential and kinetic

energy which is, gravitational potential

energy at the top is equal to kinetic

energy just before reaching the ground.

This is because no energy can be lost or

created and there is only one

transformation made which is GPE into

KE. The law of conservation of energy

can also provide a link between GPE and

work where the amount of energy

needed to lift something up is equal to

its GPE. The same goes for work and KE

where you throw a ball and the energy

needed to throw the ball is equal to its

kinetic energy.

POWER: in terms of energy transfer and work done

Power=energy transfer/time taken

·        “Power” is the amount of energy something can transfer in a given period of time

·        The units for power are watts (W) and joules per second (J/s)

·        E.g. A washing machine has 2000 watts. This means that it uses 2000 joules per

second.

Jake Smith 10R06M

4.16 - Energy Transfers in Electricity GenerationHuman beings use many methods to convert raw energy to more usable forms. Some of thesemethods are more technologically advanced, while others have been used for a long time. Most ofthese methods result ultimately in the generation of electrical energy. Energy in this form is usefulfor many different appliances, ranging from household air-conditioning to powerful roboticmachinery.Energy cannot be destroyed nor created. Therefore, electricity is just another form of the energypresent before the transferring processes. For example, wind is harnessed to generate electricity.The kinetic energy of the wind drives a turbine which causes electron movement. This movement isbasically electricity. Likewise:

Hydroelectrical: gravitational potential (water at the top of a dam) à kinetic (water flows downwards)à mechanical (turbines spin) à electrical energy

Wave: kinetic (waves move air) à mechanical (turbines spin) à electrical energy

Tidal: kinetic (tides) à mechanical (turbines spin) à electrical energy

Geothermal: thermal (heat from earth heats up water) à mechanical (turbines spin due to pressure) àelectrical energy

Solar cells: light (from Sun) à electrical energy (electrons in solar panels move)

Solar heating: light (from Sun) à thermal (water is heats up)

Fossil fuels: chemical potential (from decomposed remains) à thermal (fuel is burned to heat water)à mechanical (turbines spin due to pressure) à electrical energy

Nuclear: nuclear (from atoms) à thermal (water is heated up) à mechanical (turbines spin due topressure) à electrical energyOf course, some of the energy is unavoidably wasted during these processes, in forms such as sound.However, it is evident that all of these processes can provide energy for humans to use, with varyingdegrees of efficiency.