SP8 Forces doing work/SP9 Forces and their effects

Question 1

What happens to energy when a system changes?

Answer 1

It gets transferred from one form to another

Question 2

Define closed system

Answer 2

System which experiences no external forces

Question 3

Define work done

Answer 3

When external forces transfer energy into a system

Question 4

How do we calculate work done?

Answer 4

force x distance moved in the direction of the force

Question 5

Define power

Answer 5

• Rate at which energy is transferred
• can also be the rate of doing work when energy is being transferred by forces
• measured in watts W

Question 6

State the equation for power

Answer 6

work done/time taken

Question 7

What are the units for work done?

Answer 7

Joules

Question 8

Define efficiency

Answer 8

Measure of how much energy is not lost as waste

Question 9

State some examples of non contact forces

Answer 9

• gravitational attraction
• electrostatic attraction
• magnetic attraction

Question 10

State some examples of contact forces

Answer 10

• normal contact force
• friction

Question 11

Define normal contact force

Answer 11

Force acts at right angles to the surface that it is touching

Question 12

Define action reaction forces

Answer 12

Pairs of forces acting on different objects in opposite directions

Question 13

Define force field and give examples

Answer 13

Space around an object where it can affect other objects
eg: magnetic field for magnets and electric field for static electricity

Question 14

What is the difference between a vector and a scalar quantity?

Answer 14

A vector quantity has magnitude and direction, whereas scalar quantities only have magnitude

Question 15

Define scale diagrams

Answer 15

A way of working out the resultant forces or component forces by drawing a diagram where the lengths of arrows represent the sizes of the forces.

Question 16

What does the length of the arrow represent in scale diagrams?

Answer 16

Its size
–> so direction with larger arrows shows resultant forces

Question 17

What do equal arrows in opposite directions represent in a scale diagram?

Answer 17

• equal in magnitude but opposite in direction
• so the object is in equilibrium
• so it travels at a constant velocity

Question 18

What do free body diagrams represent?

Answer 18

A diagram of an object showing all the forces acting on it and the size and direction of those forces.

Question 19

What direction is the reaction force going to be in a free body diagram?

Answer 19

At right angles to the line of contact

Question 20

Define moment

Answer 20

A turning force

Question 21

What does the moment of a force depend on?

Answer 21

The size of the force and where it is applied

Question 22

State the equation for moment

Answer 22

force x perpendicular distance from pivot

Question 23

Describe what happens to the moments in a system when it is balanced

Answer 23

The sum of clockwise moments = sum of anticlockwise moments

Question 24

Define lever

Answer 24

A bar that pivots around a point and is used to transfer a force

Question 25

Define pivot point

Answer 25

A point which an object can rotate about but cannot move away from

Question 26

What does a gear affect?

Answer 26

Speed, force or direction

Question 27

What direction will the second gear turn towards?

Answer 27

The opposite direction to that of the first gear

Question 28

What are the effects of lubrication?

Answer 28

Reduces friction so will reduce unwanted energy