Acceleration (Also seen in Physics 2)
Acceleration is the rate at which the velocity changes. Since velocity is a vector quantity, so is acceleration.
With all vectors, the direction is important. In questions we decide which direction is positive (e.g. +ve)
If a moving object has a positive velocity: * a positive acceleration means an increase in the velocity
- a negative acceleration means a decrease in the velocity
(it begins the ‘speed up’ in the other direction)
If a moving object has a negative velocity: * a positive acceleration means an increase in the velocity
(it begins the ‘speed up’ in the other direction)
- a negative acceleration means a increase in the velocity
If an object accelerates from a velocity of u to a velocity of v, and it takes t seconds to do it then we can write the equations as it may also look like this where Δ means the ‘change in’
Acceleration is measured in metres per second squared, m/s2
Uniform Acceleration
In this situation the acceleration is constant – the velocity changes by the same amount each unit of time.
For example: If acceleration is 2m/s2, this means the velocity increases by 2m/s every second.
| Time (s) | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
|---|---|---|---|---|---|---|---|---|
| Velocity (m/s) | 0 | 2 | 4 | 6 | 8 | 10 | 12 | 14 |
| Acceleration (m/s2) | 2 | 2 | 2 | 2 | 2 | 2 | 2 |
Non-Uniform Acceleration
In this situation the acceleration is changing – the velocity changes by a different amount each unit of time.
For example:
| Time (s) | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
|---|---|---|---|---|---|---|---|---|
| Velocity (m/s) | 0 | 2 | 6 | 10 | 18 | 28 | 30 | 44 |
| Acceleration (m/s2) | 2 | 4 | 6 | 8 | 10 | 12 | 14 | |
| Section 4 | Motion Graphs | |||||||
| Lesson 5 | ||||||||
| Learning Outcomes | To be able to interpret displacement-time and velocity-time graphs | |||||||
| To be able to represent motion with displacement-time and velocity-time graphs | ||||||||
| To know the significance of the gradient of a line and the area under it | M.BENYOHAI |
Before we look at the two types of graphs we use to represent motion, we must make sure we know how to calculate the gradient of a line and the area under it.