Topic 1: Forces and Motion

Question 1

What are the typical speeds for different transport methods?

Answer 1

Walking - 1.4 m/s
Running - 3 m/s
Cycling - 5.5 m/s
Cars (built up area) - 13 m/s
Aeroplanes - 250 m/s
Cars (on a motorway) - 31 m/s
Trains - 55 m/s
Wind speed - 5 to 20 m/s
Speed of sound in air - 340 m/s
Ferries - 15 m/s

Question 2

What’s are vectors and scalars?

Answer 2

Vector - a quantity that has direction and magnitude
Scalar - a quantity that has magnitude but no direction

Question 3

What’s acceleration?

Answer 3

The change in velocity in a certain amount of time

Question 4

What’s the equation for acceleration?

Answer 4

a = (v-u) –> Acceleration = (Final velocity - initial velocity)
——- —————————————–
t Time

Question 5

What’s the equation for uniform (constant) acceleration?

Answer 5

2 x Acceleration x Distance = Final velocity squared - Initial Velocity squared

Question 6

Which acceleration equation should you use if you are given the distance?

Answer 6

Uniform acceleration

Question 7

Which acceleration equation should you use if you are given the time?

Answer 7

a = v-u/t

Question 8

How do you find the Speed on a distance/time graph, when it is a straight line?

Answer 8

Gradient = change in vertical/change in horizontal

Question 9

How do you find the average speed on a distance/time graph when the line is non-uniform (e.g. accelerating)?

Answer 9

Distance/time

Question 10

How do you find the speed on a distance/time graph if the line is curved?

Answer 10

Draw a tangent and find the gradient of it

Question 11

What’s a force?

Answer 11

A push/pull that acts on an object due to the interaction with another object (vector)

Question 12

What’s a contact force?

Answer 12

A force that acts when objects are physically touching

Question 13

What’s a non-contact force?

Answer 13

A force that acts when objects are not touching

Question 14

What are the three non-contact forces?

Answer 14

Gravitational force
Electromagnetic force
Magnetic force

Question 15

When do forces arise?

Answer 15

Forces arise from an interaction between two objects.
When two objects interact both experience a force.

Question 16

What is friction?

Answer 16

Friction is the interaction between two surfaces that slide relative to each other
Each surface experiences a force in the direction that prevents relative movement.

Question 17

What is normal contact force?

Answer 17

There is an interaction between an object and the surface it is resting on.
The object pushes down on the surface and the surface pushes up on the object with an equal force.

Question 18

What’s that resultant force?

Answer 18

The single force that could replace all forces acting upon an object

Question 19

How do you calculate the resultant force if it is not on a straight line?

Answer 19

(draw on graph paper, measure with a ruler the hypotenuse of the 2 forces) - triangle thingy: 1cm = 1 N

Question 20

What is newton’s second law?

Answer 20

The acceleration of an object is proportional to the resultant force of the object and inversely proportional to the mass of the object (f = ma)

Question 21

What is weight?

Answer 21

The force acting on an object due to gravity
weight = mass x gravitational field strength

Question 22

What apparatus can be used to measure weight?

Answer 22

Newton Meter

Question 23

What’s Newton’s third law?

Answer 23

When two objects interact, the forces they exert on each other are equal and opposite

Question 24

How can you investigate the effect of varying the force on the acceleration of an object?

Answer 24

CORE PRACTICAL:
- Measure the mass of a trolley and the hanging hook, and set up the trolley onto a ramp (measure the height)
- Set up two light gates, one at the start, one at the end
- As the trolley begins to move, the first light gate will record the initial speed
- Attach the trolley to the hanging mass by the string and let go
- Each light gate will record he time and the speed at that time
- Then calculate the acceleration using acceleration = change in speed/ time
- Repeat with more weight in even intervals

Question 25

Explain how safety features in vehicles work

Answer 25

• Increase collision time which reduces the force and risk of injury
• e.g. crumple zones increase time taken to stop which decreases its deceleration, reducing the force
• Air bags slow you down gradually

Question 26

How do vehicles skid?

Answer 26

• Brakes of a vehicle do work on its wheels which transfers energy from the vehicle’s kinetic energy store to the thermal energy store of the brakes
• Large decelerations may cause the brakes to overheat, so they don’t work as well and could also cause the vehicle to skid

Question 27

Explain velocity when an object moves in a circle

Answer 27

• If an object is travelling in a circle at a constant speed, it’s constantly changes direction so its velocity constantly changes. So, it’s accelerating
• The resultant force acts towards the centre of the circle and keeps the object moving (centripetal force)

Question 28

What’s Inertia?

Answer 28

The tendency for the motion of an object to remain unchanged
e.g. objects with large mass like the moon have a lot of inertia

Question 29

What’s inertial mass?

Answer 29

How difficult it is to change an object’s velocity (force/acceleration)

Question 30

What’s the stopping distance?

Answer 30

distance between the driver spotting a hazard and the vehicle coming to a complete stop: Thinking distance + braking distance

Question 31

What’s the thinking distance?

Answer 31

The distance the car travels in the time between noticing the hazard and applying the brakes, affected by:

• Reaction time increased by tiredness, alcohol, drugs…
• speed: the faster you’re going the further you’ll travel during reaction time

Question 32

What’s the braking distance?

Answer 32

the distance taken to stop once the brakes have been applied, affected by:
- Speed
- Mass
- Condition of brakes
- Friction between tyres and road