Forces

Question 1

What is a force?

Answer 1

Something that can change the motion of an object

It is measured in Newtons (N)

Question 2

What 3 ‘laws’ can be used to describe all forces?

Answer 2

1. An object will remain at rest or travelling at a constant speed unless a resultant force acts on it.
2. F = MA
3. Every action has an equal and opposite reaction

Question 3

What is a resultant force?

Answer 3

The combined effect/overall effect of the forces acting on an object

Question 4

What does it mean when the resultant force of an object is 0?

Answer 4

• If the object is at rest, it will stay at rest
• If the object is moving, it will continue doing so at the same speed and in the same direction

Question 5

What does it mean if the resultant force on an object is not 0?

Answer 5

The object is accelerating

Therefore:

• If the object is at rest, it will accelerate in the direction of the resultant force
• If the object is moving in the same direction as the resultant force, it will accelerate in that direction
• If the object is moving in the opposite direction to the resultant force, it will decelerate

Question 6

If an object is accelerating, what can it be doing?

Answer 6

• Speeding up
• Slowing down
• Chaning direction

Question 7

What is acceleration?

Answer 7

Change in velocity per second (m/s²)

The can be changed by the object chaning either speed or direction

Question 8

What is stopping distance?

Answer 8

Thinking distance + braking distance

Question 9

What is thinking distance?

Answer 9

The distance traveled by a vehicle in the time it takes the driver to react to a stimulus

Question 10

What is braking distance?

Answer 10

The distance traveled by the vehicle in the time between the brakes being applied and the vehicle actually stopping

Question 11

What affects thinking distance?

Answer 11

• Tiredness
• Drugs
• Reaction time
• Speed at which the car is traveling

Question 12

What affects braking distance?

Answer 12

• Poorly maintained roads
• Bad weather conditions
• The conditions of the car (e.g. worn brakes)

Question 13

What is weight?

Answer 13

The force of gravity acting upon an object

Question 14

What is the extension of a spring?

Answer 14

The difference between the length of the spring and its original length

Question 15

What happens when an object falls through a fluid?

Answer 15

• Drag force is exerted on the object, resisting its motion
• The faster the object falls, the bigger the drag force becomes
• Eventually it will be equal to the weight of the object
• The resultant force on the object is now 0, so it stops accelerating
• It moves at a constant velocity so has reached its terminal velocity

Question 16

What is an elastic object?

Answer 16

An object that regains its original shape when the forces deforming it are removed

Question 17

What is the relationship between the extension of a spring/elastic object and the force applied to it?

Answer 17

They are directly proportional until the limit of proportionality is reached/exceeded

Question 18

What is the limit of proportionality?

Answer 18

The limit of Hooke’s law applied to the extension of a spring

Question 19

What is Hooke’s law?

Answer 19

The extension of an elastic object/spring is directly proportional to the force applied provided the limit of proportionality is not exceeded

Question 20

What is the spring constant (k) measured in?

Answer 20

N/m

Question 21

What happens to an elastic object/spring when the stretching force is removed?

Answer 21

The stored elastic potential energy is released as another type of energy

Question 22

Complete the sentence:

The stiffer the spring…

Answer 22

…the greater its spring constant

Question 23

What is fuel economy?

Answer 23

Reducing the amount of fuel a vehicle uses to travel a particular distance

Question 24

Why does reducing air resistance improve fuel economy and how can this be done?

Answer 24

• By making a car more streamlined
• Means less energy and power is needed to maintain a certain speed
• Therefore less fuel is used

Question 25

What causes skidding?

Answer 25

• When the brakes on a vehicle are applied too harshly
• When a vehicle skids, the wheels lock and slide along the road surface
• This increases stopping distance

Question 26

What can be done to reduce skidding?

Answer 26

• Use anti-skid road surfaces
• These are rougher than normal surfaces
• This increases the friciton between tyres and the road
• They are used in places where drivers are likely to brake, such as near traffic lights and road junctions

Question 27

What are speed cameras used for and how do they work?

Answer 27

• Used to discourage motorists from speeding
• Can determine the speed of a motorist at a particular point
• Can also be used in pairs to determine the speed at two points, and so can calculate an average speed
• Motorists going above the speed limit will be fined and may lose their licence