Physics Module 3 - Motion

Speed

How fast something is moving, regardless of direction.

Displacement

How far an object traveled from its starting position in a given direction.

Velocity

The rate of change of an objects displacement (speed but in a given direction).

Acceleration

The rate of change of an objects velocity.

Instantaneous speed

The speed of an object at any given point.

If a tile falls from a roof 25 m high. Calculate its speed when it hits the ground and how long it takes to fall.

V = 22.1 ms-1

t = 2.26 s

How would you measure the acceleration due to gravity?

The Method:

1. Measure the height,h from the bottom of the ball bearing and the top of the trap door.

2. Flick the switch that simultaneously starts the timer and disconnects the electromagnet, releasing the ball bearing.

3. The ball will then fall, knocking the trap door down, breaking the circuit which will stop the timer

4. Use the time, t measured and the height, h that the ball bearing has fallen to calculate the value of g, using the equation h = ½ gt²

Errors:

Parallax error (when determining the height), can be avoided by using a set square to ensure eye is level with the ruler.

How would you go about solving a projectile when it is at an angle?

Method:

1. Resolve the initial velocity into horizontal and vertical components (draw them on the diagram).

2. Use the vertical component to work out how long the object is in the air and/or how high it goes.

3. Use the horizontal component to work out how far it goes whilst its in the air.

How would you find the velocity of an object from its displacement-time graph? (straight line graph)

Velocity = Gradient = Change in displacement/change in time

How would you find the velocity of an object from its displacement-time graph? (curved graph)

Velocity = Gradient of tangent to the curve = Change in displacement/time

How would you find the acceleration from a velocity-time graph?

Acceleration = Gradient = Change in velocity/time taken

What is the gradient under a velocity-time graph equal to?

Displacement, if the graph is curved, split the graph into trapeziums and triangles to approximate the area underneath the graph.

How would you investigate what affects the motion of a trolley on a slope?

Method:

1. Measure the length of the trolley

2. Mark a start line on the ramp to make sure the trolley will always start in the same position to ensure a fair test.

3. Measure the angle of the ramp and the distance from the chosen start line to the light gate.

4. Place the trolley on the ramp at its starting position, let go of it so its initial velocity, u is 0.

5. The data logger will then record the time taken for the trolley to pass through the light gate and then calculate the velocity of the trolley as it passes through the gate.

6. Change the starting position of the trolley so the distance, d is varied.

7. Repeat this experiment for each distance 3 times and average the recorded velocities to minimize the error in the final result.

When investigating the motion of a trolley on a slope, what other factors can you change?

1. Change the angle of the ramp

2. Change the mass of the trolley by adding weights to it

3. Change the shape and the size of the trolley

4. Change the ramp material to investigate how friction will affect the motion.

How could you investigate how collisions affect the motion of a trolley?

1. Set up a video camera, a ramp, a wall and mark the starting position of the trolley.

2. Measure the length of the trolley.

3. Turn on the video camera and start the recording.

4. Place the trolley on the ramp and line it up with the start line. Let go of it so its initial velocity, u is equal to 0.

5. Once the trolley has hit the wall and it is at rest, stop recording.

6. Use the equation: Time taken for the trolley to pass the point = Number of frames for a trolley to pass the point x 1 second/Frame rate of camera.

Thinking Distance

The distance the vehicle travels during the drivers reaction time.

Braking Distance

The distance the vehicle travels after the brakes are applied until it comes to a complete stop.

Stopping Distance

Thinking distance + Braking distance

What factors might affect the thinking distance?

1. Tiredness

2. Alcohol or drug use

3. Illness

4. Distractions (loud noises, etc.)

What factors might affect the braking distance?

1. Tyre conditions (worn out tires)

2. Road conditions (icy roads, lack of friction)

3. Mass (the heavier the vehicle, the longer it will take to slow down to a complete stop)

4. Braking Force