Physics P2 1

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?

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?

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?

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?