# Physics P2 1

Revision cards for AQA Physics unit 2, section 1 - Motion

• Created by: Tasha
• Created on: 02-04-11 11:09

## Distance-time graphs

Key Points
1. The steeper the line on a distance-time graph, the greater the speed it represents
2. Speed (metre/second, m/s) = distance travelled (metre, m)
time taken (seconds, s)

- We can use graphs to help us describe the motion of a body.
- A distance time graph shows the distance of a body from a starting point (y-axis) against time taken
(x-axis).
- The slope of the line on a distance-time graph represents speed.
- The steeper the slope, the greater the speed.
- The speed of a body is the distance travelled each second.
- We can calculate the speed of a body using this equation: speed = distance
time
- The SI unit of speed is metres per second (m/s)

Check Yourself
1. What does the slope of the line on a distance-time graph represent?
2. What is the equation that relates speed, distance and time?
3. What is the SI unit of speed?

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## Velocity and acceleration

Key points
1.
Velocity is speed in a given direction
2. Acceleration is change of velocity per second
3. A body travelling at a steady speed is accelerating if its direction is changing

- The velocity of a body is its speed in a given direction. If the body changes direction it changes velocity,
even if the speed stays the same.
- If the velocity of a body changes, we say that it accelerates.
- We can calculate acceleration using the equation: acceleration =   change in velocity
time taken for change
- The SI unit of acceleration is metres per second squared (m/s2).
- If the value calculated for acceleration is negative, the body is decelerating - slowing down.

Check yourself
1.
What is the difference between speed and velocity?
2. What is the SI unit of acceleration?
3. What do we mean by deceleration?

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Key Points
1.
The slope of a line on a velocity-time graph represents acceleration
2. the area under the line on a velocity-time graph represents distance travelled

- A velocity-time graph shows the velocity of a body (y-axis) against time taken (x-axis).
- The slope of a line on a velocity-time graph represents acceleration.
- The steeper the slope, the greater the acceleration.
- If the slope is negative, the body is decelerating
- The area under the line on a velocity-time graph represents the distance travelled in a given time.
- The bigger the area, the greater the distance travelled

Check Yourself
1.
What does a horizontal line on a velocity-time graph represent?
2. What would the velocity-time graph for a steadily decelerating body look like?
3. What does the area under the line on a velocity-time graph represent?

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## Using graphs

Key Points
1.
The slope of the line on a distance-time graph represents speed.
2. The slope of the line on a velocity-time graph represents acceleration.
3. The area under the line on a velocity-time graph represents the distance travelled.

- If you calculate the slope of the line on a distance-time graph for an object, the answer you obtain will be the speed of the object. Make sure that you use the numbers from graph scales in your calculations.
- If you calculate the slope of the line on a velocity-time graph for an object, the answer you obtain will be the acceleration of the body. Make sure you use the numbers fron graph scales in your calculations.
- Calculating the area under the line on a velocity-time graph between two times gives the distance travelled between those times.

Check Yourself

The graph shows the motion of a car
1. What is the initial speed of the car?
2. What is the final speed of the car?
3. What is the acceleration of the car?

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