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Motion
- Speed (ms-1)= Distance/ Time
- A distance-time graph can make it easier to represent motion
- A velocity (speed in a given direction) – time graph can show the instantaneous speed
Distance and displacement
- DISTANCE – the length of the path you have taken
- DISPLACEMENT – the straight line distance between two places
- To describe displacement, you need to say how far you are away from the start and
- Scalar – only size or magnitude
- Vector quantity – size and direction
- Acceleration is the rate of change of velocity with time, so it is also a vector. Acceleration happens when there is:
- A change in SPEED, or
- A change in DIRECTION, or
- A change in speed AND direction
- If an objects speed is constant but its velocity is changing, we say it is also accelerating
- With a train travelling at a constant speed in a circle, it is considered to be accelerating but its average velocity as it goes round the track back to its starting point is zero, as its DISPLACEMENT is ZERO
Graphs of motion
- When something decelerates, it is negative acceleration, so -1 ms-2 A straight line on a velocity time graph is UNIFORM acceleration
ACCELERATION – the rate of change of velocity with time
The graph shows the motion of a ball being thrown up in the air, falling, and then being caught.
- A – The ball is at rest
- A to D – the ball is thrown up with a uniform upward acceleration
- D to B – it has a negative acceleration as the ball accelerates downwards until resting at B
- B to E – the same velocity as D to B but it is negative as it accelerates down
- E – The ball is caught and brought to rest by C
Non-linear graphs (curved graphs) – make strips/rectangles under the graph, calculate the area and add it up
'this is less accurate than a linear graph'
Equations of motion
And we're all done for today!