# 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?

## Velocity and acceleration

**Key points1.** 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?

## More about velocity-time graphs

**Key Points1.** 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 Yourself1.** 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?

## Using graphs

**Key Points1.** 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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