Speed and Velocity
To work out velocity, speed, displacement or time taken, use this:
- The 'D' represents 'Displacement'
- The 'S' represents 'Velocity' or 'Speed' (Both calculations are the same in this case)
- The 'T' represents 'Time'
Bear in mind that 'm/s' (metres per second) is used for both, speed and velocity. (E.g 40 m/s) However, velocity is a vector quantity, which means it also needs a direction. (E.g 40 m/s North)
Acceleration is how quickly velocity is changing.
The unit for acceleration is m/s².
To work out acceleration use this:
In order to work out the change in velocity, you need to use this:
Change in velocity = Finishing velocity (m/s) - Initial velocity (m/s)
For example, A skulking cat accelerated from 2m/s to 6m/s in 5.6s. Find it's acceleration.
Answer: Using the formula,
Acceleration = (v - u) / t = (6 - 2) / 5.6 = 4 / 5.6 = 0.71 m/s²
'V' represents the finishing velocity, 'U' represents the initial velocity.
Velocity Time Graphs
Here is a typical velocity time graph:
Velocity Time Graphs Continued...
Things to remember about velocity time graphs:
- Gradient = Acceleration
- Flat sections represent steady speed
- The steeper the graph, the greater the acceleration or deceleration
- Uphill sections (/) are acceleration
- Downhill sections (\) are deceleration
- The area under any section is the distance travelled in that time interval
- A curve means changing acceleration.