Section 4 - Forces And Energy

Question 1

When a system changes, what happens to energy?

Answer 1

It is transferred

Question 2

What is a system?

Answer 2

A single object or a group of objects that you’re interested in

Question 3

When a system changes, what happens to some of the energy?

Answer 3

A small amount of energy is dissipated and stored in less useful ways

Question 4

What are the three ways in which energy be transferred?

Answer 4

Heating
Doing work
Electrical equipment

Question 5

How can energy be transferred by heating?

Answer 5

E.g. a pan of water is heated on a stove

When the system is the pan of water, energy is transferred into the system by heating to the thermal energy stores, which increases the temperature

When the system is the stove and the pan, energy is transferred from the chemical energy store of the gas to the thermal energy stores of the pan and the water

Question 6

How is energy transferred by doing work?

Answer 6

E.g. a box being lifted off of the floor

The box is the system. As the box is lifted, work is done against gravity

This causes energy to be transferred to the box’s kinetic and gravitational potential energy stores

Question 7

How is energy transferred by electrical equipment?

Answer 7

Electrical devices work by transferring energy between two different energy stores

E.g. electric ions transfer energy electrically from the mains power supply to the thermal energy store of their metal plates

Question 8

If a force moves an object, what has been done?

Answer 8

Work

Question 9

What is the equation for work done?

Answer 9

Force x distance moved in the direction of the force

Question 10

What is work done?

Answer 10

When a force moves an object through a distance, work is done on the object and energy is transferred

Question 11

What does Nm mean?

Answer 11

Newton metre

Question 12

What is power?

Answer 12

How much work is done per second / rate of energy transfer

Question 13

What is the equation for power?

Answer 13

Work done (J) / time taken (s)

Question 14

The larger the power of an object, the more work it does per second

True or false?

Answer 14

True

Question 15

A force doing work often causes a rise in what?

Answer 15

Temperature as energy is dissipated to the thermal energy stores of the moving object and its surroundings. This means that the process is wasteful and the efficiency of the process is reduced

Question 16

Interactions between objects causes what?

Answer 16

Forces

Question 17

Whenever two objects interact, both objects feel an equal but opposite force. What law is this?

Answer 17

Newton’s third law

Question 18

What do free body force diagrams show?

Answer 18

All of the forces acting on an object

Question 19

What is the resultant force?

Answer 19

The overall force on a point or object

Question 20

Objects in equilibrium have a resultant force of what?

Answer 20

Zero. Objects in equilibrium are either stationary or moving at a steady speed (Newton’s first law)

Question 21

How do you find resultant forces?

Answer 21

By using scale drawings

Question 22

An object is in equilibrium if what?

Answer 22

The forces acting upon it are balanced

Question 23

What can you split a force into?

Answer 23

Components

Question 24

Why do you sometimes split forces into components?

Answer 24

Not all forces act horizontally or vertically - some act at awkward angles

To make these easier to deal with, we split them into two components at right angles to each other

Acting together, these components have the same effect as the single force

Question 25

What is a moment?

Answer 25

The turning effect of a force

Question 26

How do you work out a moment?

Answer 26

Force x distance

Question 27

The sum of clockwise moments =

Answer 27

The sum of anticlockwise moments

Question 28

What do levers do?

Answer 28

Make it easier for us to do work

Question 29

Gears fit together to transmit what?

Answer 29

Turning effects