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Question 1

What are the 8 energy stores you need to know?

Answer 1

Thermal Chemical
Kinetic Magnetic
Grav Po Electrostatic
Elastic Po Nuclear

Question 2

How is energy transferred? (4 ways)

Answer 2

Mechanically (by a force doing work)
Electrically (work done by moving charges)
By heating or by radiation

Question 3

Explain how when a system ( a single or group of objects) changes, energy is transferred?

Answer 3

When a system changes, energy is transferred.
It can be transferred into or away from the system.
or between different objects in the system
or between different types of stores.

Question 4

What is a closed system?

Answer 4

Where neither matter nor energy can enter or leave.

Net change in total energy is always zero

Question 5

Explain how energy can be transferred by heating? (Example: kettle boiling water)

Answer 5

The water is the system.
Energy is transferred to the water (from kettles heating element) by heating, into the waters thermal energy store (temp rises therefore).

Question 6

What is work done?

Answer 6

Work done is another way of sauing energy transferred

Question 7

When a system changes, energy is transferred by doing work. When is work done?

Answer 7

Work can be done when current flows (work is done against resistance in a circuit) or by a force moving an object)

Question 8

Examples of work being done (Person throwing a ball, friction of cars brakes and wheels, collision between two cars)

Answer 8

–The Initial force exerted by person to through a ball upwards does work. Causes an energy transfer from chemical of persons arm to kinetic store of ball and arm.

–Friction between a car’s brakes and its wheels does work as it slows down. Causes energy transfer from wheels kinetic store to thermal store of surroundings.

– In Collision between car and stationary object, normal contact force between car + object does work. Causes energy transferred from car’s kinetic store to other energy stores. (Thermal stores of car and object)

Question 9

Kinetic energy: Fact File

Answer 9

::: Anything moving has energy in its kinetic energy store
::: Energy transfers to this store when objects speed up and is transferred away when slows down
::: Energy in kinetic energy store depends on objects mass and speed
::: The greater the mass, the faster its going, the more emergy there will be in its kinetic energy store.

Question 10

Grav Potential Energy store: Fact File

Answer 10

::: lifting an object in grav field requires work
::: Causes transfer of energy to the G.P.E of the raised object ( higher it is, more energy transferred)
::: amount of energy in g.p.e store depends on mass, height, stength of grav field

Question 11

How do falling objects transfer energy?

Answer 11

When an object falls, energy is transferred from the G.P.E store to the kinetic energy store.
When theres no air resistance:
ENERGY LOST FROM G.P.E STORE = ENERGY GAINED IN THE KINETIC ENERGY STORE
( air resistance acts against falling objects so some energy is transferred to other stores.)

Question 12

How does stretching transfer energy to the elastic potential energy store?

Answer 12

Stretching an object transfers energy to its elastic potential energy store so long as the limit of proportionality has not been exceeded

Question 13

What is the conservation of energy principle?

Answer 13

Energy can be transferred usefully, stored or dissipated, but can never be created or destroyed.

Question 14

What is useful energy and wasted energy?

Answer 14

Useful energy is energy transferred to ehere it is wanted in the way that is wanted but WASTED energy is energy that is not usefully transferred.

Question 15

What is dissipated energy.

Answer 15

Dissipated energy is basically wasted energy as it is being stored in a not useful way.

Question 16

Example of energy being transferred usefully and not usefully (mobile phone)

Answer 16

A mobile is a system.
When used, energy is usefully transferred from the chemical energy store of the battery in the phone.
Some of the energy is dissipated in this transfer to the thermal energy store of the phone.

Question 17

Describe energy transfers for closed systems for wehn a cold spoon is dropped in a insulated flask of hot soup.

Answer 17

When a cold spoon is dropped in a insulated flask of hot soup , which is sealed.
You can assume the the flask is a perfect thermal insulator so the spoon and soup form a closed system.
Energy transferred from thermal energy store of the soup to the useless thermal energy store of spoon. No energy has left the system, so net change in energy store is 0.

Question 18

What is power?

Answer 18

Power is the rate of energy transfer, or the rate of doing work.

Question 19

What is power measured in?

Answer 19

Power is measured in watts. One watt = 1 joule of energy transferred per second

Question 20

Why are useful devices useful?

Answer 20

Because they can transfer energy from one store to another.

Question 21

What is efficiency?

Answer 21

Efficiency is if there is less energy wasted in the store, the more efficient the device is said to be

Question 22

How csn you improve the efficiency of an object?

Answer 22

By insukating objects, lubricsting them or making them more streamlined.

Question 23

Describe the efficiency of an object in terms of total input and ouput of energy?

Answer 23

Useful energy output is not usually equal to the total energy input.
No device is 100% efficient and the wasted energy is usually transferred to useless thermal stores.

Electrical heaters are the only exception. Usually 100% efficient because all energy in electrostatic store is transferred to useful thermal energy stores.