1What is a mechanical process?
When a force acts on an object (pushing, pulling, stretching, squashing)
2How is energy wasted during a mechanical process?
Friction can cause sound and an increase in temperature
Heats the surroundings/energy is dissipated
3Examples of energy being dissipated
Friction
Light
Sound
- transferring energy to the thermal store of the surroundings
4Useful energy
An energy transfer used for an intended purpose
(Note: Somtimes energy can be usefully dissipated to the surroundings)
5Wasted energy
An energy transfer that is not used for intended purpose
and is dissipated to the surroundings
6Useful energy in a television
Energy is dissipated to the surroundings by radiation (visible light) and by heating (sound waves)
7Wasted energy in a television
Energy from thermal store of television is dissipated to the surroundings by heating
8Useful energy in heater
Energy from thermal store of heater is dissipated to the surroundings by heating
9Why is reducing energy loss in home appliances important?
(Electrical) Energy can be expensive
Fossil fuels are used to produce electricity
Fossil fuels contribute to global warming
10Main source of wasted energy in machines
Friction
11How can you reduce wasted energy in machines
Lubricate parts that rub together (chains in bikes, wheels)
12What determines the effectiveness of an insulator?
Conductivity
Density
Thickness
13How does conductivity affect the effectiveness of an insulator? Why?
Lower conductivity = better insulator.
Lower conductivity means less energy transferred.
14How does density of a material affect the effectiveness of an insulator? Why?
Less dense = better insulator
In denser materials, particles are closer together so energy is more easily transferred
15How does thickness affect the effectiveness of an insulator?
Thicker material = better insulator.
16How do you lower the rate of cooling
Use insulation, energy is transferred to the surroundings more slowly
17What makes fibre glass a good insulator for houses?
Air trapped between fibres
18How can you keep hot water hotter for longer?
Use insulation (like a styrofoam cup)
19Explain how thermal conduction works
Energy is transferred by vibrating particles
Vibrating particles transfer energy from their kinetic store to the kinetic store of neighbouring particles
Always from hot to cold
20Thermal equilibrium
Objects will continue to lose heat until they have the same temperature as the surroundings
21Conductivity of metals and non-metals
Metals - good conductivity - good conductors
Non-metals - poor conductivity - good insulators
22How does the temperature difference affect the rate of thermal conduction
The greater the temperature difference, the greater the rate of thermal conduction
23Efficiency Equation (Answer as a ratio)
Efficiency = useful energy transferred (J) / total energy supplied (J)
24Efficiency Equation (Answer as a percentage)
Efficiency (%) = (useful energy transferred (J) / total energy supplied (J)) x 100
25(HT) Machines waste energy due to…
Friction
Air resistance
Electrical resistance
Noise
26(HT) How friction causes wasted energy
Friction produces heat.
The thermal energy is dissipated to the surroundings
27(HT) How to reduce friction in a mechanical system
Add bearings
Lubricate parts
28(HT) How does electrical resistance cause wasted energy
When a current flows, resistance causes wires to heat.
The thermal energy is dissipated to the surroundings.
29(HT) How to reduce electrical resistance in a mechanical system
Using components with lower resistance
Reducing the current
30(HT) How air resistance causes wasted energy
Causes friction (heating) between moving object and air
The thermal energy is dissipated to the surroundings
31(HT) How to reduce air resistance in a mechanical system
Streamline the shape of moving object
32(HT) How noise causes wasted energy
Sound waves cause air particles to vibrate (and heat up)
Thermal energy is dissipated to the surroundings
33(HT) How can sound be reduced in a mechanical system
Tightening loose parts to reduce vibration
Lubricating parts