Motion Key Definitions

Question 1

Acceleration

Answer 1

The rate of change of velocity

Question 2

Average speed

Answer 2

Distance over time for the entire region of interest

Question 3

Braking distance

Answer 3

The distance travelled between the brakes being applied and the vehicle coming to a stop. It is affected by the vehicle and road conditions.

Question 4

Displacement

Answer 4

The direct distance between an objects starting and ending positions. It is a vector quantity and has both a direction and a magnitude

Question 5

Displacement time graphs

Answer 5

Plots showing how displacement changes over a period of time. The gradient gives the velocity. Curved lines represent an acceleration.

Question 6

Free fall

Answer 6

An object is said to be in free fall when the force only acting on the object is due to gravity.

Question 7

Instantaneous speed

Answer 7

The exact speed of an object at a specific given point

Question 8

Projectile motion

Answer 8

The motion of an object that is fired from a point and then upon which only gravity acts. When solving projectile motion it is important to split the motion into vertical and horizontal components.

Question 9

Reaction time

Answer 9

The time taken to process a stimulus and trigger a response to it. It is affected by alcohol, drugs and tiredness.

Question 10

Stopping distance

Answer 10

The sum of thinking distance and breaking distance for a driven vehicle

Question 11

Thinking distance

Answer 11

The distance travelled in the time it takes for the driver to react. It is affected by alcohol, drugs and tiredness.

Question 12

Velocity time graphs

Answer 12

Plot shows how velocity changes over a period of time. The gradient gives acceleration. Curved lines represent changing acceleration.

Question 13

Velocity

Answer 13

The rate of change of displacement. It is a vector quantity and so has both direction and magnitude

Question 14

Describe how terminal velocity of an object can be determined using light gates

Answer 14

1. Set up light gates vertically and measure the distance between them
2. Connect them to a data logger and then release an object from rest above them, measuring the time it takes for the object to travel between the two gates

3 Using the time and the known distance, you can calculate the velocity of the falling object.

Question 15

Describe how the light gates can also be used to investigate conservation of momentum

Answer 15

1. Place two cards on a linear air track to reduce friction with repelling magnets so that they do not stick together
2. Attach a card to the top of each cart so that they break the beams of the light gates when they pass
3. Keep one cart stationary and push the other towards it, measuring its velocity before the collision.
4. The measure the velocity of both carts after the collision and calculate the momentum before and after.

Question 16

Define ‘g’

Answer 16

The acceleration of free fall, ‘g’, is the acceleration of an object in response to the gravitational attraction between the Earth and the object. g = 9.81m s-2.

Question 17

Describe the experiment in which one can determine ‘g’ using an electromagnet

Answer 17

1. An electromagnet holds a steel ball suspended a measured distance above a surface, then start the timer when the electromagnet is deactivated, and stop it when the surface is hit.

As the ball was initially resting, u = 0

The distance and tie are known, so we can use a SUVAT equation

Calculate ‘a’ which in this case is ‘g’

Question 18

A ball if projected off a castle at 6m/s. How does it’s horizontal velocity change from its launch until it hits the ground?

Answer 18

The horizontal velocity remains the same as there is no acceleration in the horizontal direction

Question 19

In projectile motion, what is the vertical acceleration?

Answer 19

The vertical acceleration is equal to gravitational field strength ‘g’ downwards.