Energy Stores and Systems

Question 1

Is energy ever used up? What happens to it?

Answer 1

No. Energy is never used up. It is just transferred between different energy stores and different objects.

Question 2

What happens to energy when it is transferred?

Answer 2

The energy is stored in one of the object’s energy stores.

Question 3

What are the energy stores needed to be known?

Answer 3

Thermal energy stores / Kinetic energy stores / Gravitational potential energy stores / Elastic potential energy stores / Chemical energy stores / Magnetic energy stores / Electrostatic energy stores / Nuclear energy stores.

Question 4

Energy is mechanically transferred. What does that means?

Answer 4

It is transferred by a force doing work.

Question 5

Energy is electrically transferred. What does that means?

Answer 5

It is transferred through work done by moving charges.

Question 6

Energy is transferred by heating or by radiation. What does that means?

Answer 6

It means energy is transferred y light or sound.

Question 7

What happens when a system changes?

Answer 7

Energy is transferred.

Question 8

What is a system?

Answer 8

A system is just a fancy word for a single object or a group of objects that you’re interested in.

Question 9

What are closed systems?

Answer 9

Closed systems are systems where neither matter nor energy can enter or leave.

Question 9

When a system changes, energy is transferred. Where does it transfers to?

Answer 9

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

Question 10

What is the net change in the total energy of a closed system?

Answer 10

It is always zero.

Question 11

Energy can be transferred by heating. Give the example of boiling water in a kettle.

Answer 11

You can think of the water as the system. Energy is transferred to the water (from the kettle’s heating element) by heating, into the water’s thermal energy store (causing the temperature of the water to rise).

Question 12

Energy can be transferred by heating. Give the example of the kettle’s heating element and the water together as a two-object system.

Answer 12

Energy is transferred to the thermal energy store of the kettle’s heating element, which transfers energy by heating to the water’s thermal energy store.

Question 13

What does work done means?

Answer 13

Work done is just another way of saying energy transferred - they’re the same thing.

Question 14

When can work be done?

Answer 14

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

Question 15

The initial force exerted by a person to throw a ball upwards does work. What type of energy transfer it causes?

Answer 15

It causes an energy transfer from the chemical energy store of the person’s arm to the kinetic energy store of the ball and arm.

Question 16

A ball dropped from a height is accelerated by gravity. What type of work is done? What type of energy transfer is caused?

Answer 16

The gravitational force does work. It causes energy to be transferred from the ball’s gravitational potential energy store to its kinetic energy store.

Question 17

The friction between a car’s brakes and its wheels does work as it slows down. What type of energy transfer is caused?

Answer 17

It causes an energy transfer from the wheel’s kinetic energy stores to the thermal energy store of the surroundings.

Question 18

In a collision between a car and a stationary object, the normal contact force between the car and the object does work. What type of energy transfer is caused? Give an example.

Answer 18

It causes energy to be transferred from the car and the object, e.g. the elastic potential and thermal energy stores of the object and the car body. Some energy might also be transferred away by sound waves.