
The Basics of Linear Motion and Displacement and Velocity Time-Graphs
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The Basics of Linear Motion and Displacement and Velocity Time-Graphs
Both speed and velocity tell us how far something is travelling in unit time. As velocity is a vector it must also tell us what direction the object is travelling in.
Speed (m/s) = | distance moved (m)
time taken (s)
|
Velocity (m/s) = | displacement change (m)
time taken (s)
|

Acceleration tells us how rapidly something is changing velocity - for instance, the change in velocity in unit time.Deceleration is the same thing, but has a negative sign as the velocity if decreasing.


Question (easy one!):
These show the motion of an object very clearly and allow you to find position and velocity at any time. Any graph that you see will be a combination of these sections.

Notice that the gradient = | change in D (or ΔD)
change in t (or Δt)
|
= the velocity at any time. |
When the velocity is changing, as on the lower two graphs, you can find the velocity at any point by drawing a tangent touching the graph at that point by drawing a tangent touching the graph at that point and working out its gradient using the same equation.
Question:
Label the journey shown below with the correct words by dragging them onto the graph.
These are similar to displacement-time graphs, but this time velocity is on the y-axis. Here are the only possibilities that you'll come across at A-level.

Notice that the gradient = | change in V (or ΔV)
change in t (or Δt)
|
= the acceleration at any time. |
You also need to know that the area under the line gives you the displacement of the object up to that point.

Last, but not least, are the acceleration-time graphs!

Note: All three of the movement graphs are related to each other as the:
- Gradient of D/t graph gives you the points on the v/t graph.
- Gradient of v/t graph gives you the points on the a/t graph.