What is Acceleration?
Acceleration is a measure of the change in velocity of an object. When you step on the gas pedal in the car, the car will move faster and faster. This change in speed is an acceleration.
The equation for acceleration is:
Acceleration = (change in velocity)/(change in time)
or
a = Δv ÷ Δt
How to Measure Acceleration
The standard unit for measuring acceleration is meters per second squared or m/s2. You can calculate this value from the above formula with speed in meters per second and time in seconds.
Acceleration is a Vector
In physics, acceleration has not only magnitude (which is the number of m/s2 we talked about above) but also direction. This makes the acceleration a vector.
Force and Acceleration
Newton’s second law of motion states that the force on an object is equal to mass times acceleration. This is written in the following equation:
Force = mass * acceleration
or
F = ma
We can use this formula to determine acceleration if we know the mass and force acting on an object. This formula is:
acceleration = force/mass
or
a = F/m
Constant Acceleration
When an object changes speed by a constant amount with time, it is called constant acceleration. An object with constant positive acceleration will accelerate uniformly. Its speed will not stop increasing.
| Interval 1st second 2nd second 3rd second |
Acceleration 5 m/s2 5 m/s2 5 m/s2 |
Velocity 10 m/s 15 m/s 20 m/s |
An example of constant acceleration of 5 m/s2.
Free Fall: A Type of Acceleration
An example of a constant acceleration is an object in free fall. During free fall, gravity exerts a constant force on the object causing the increase in velocity to remain constant. If you measure the distance an object has fallen, it will fall more every second because it is continuously accelerating.
Note: In the real world there will be more air friction on the object. At some point, the object will reach “final velocity”. This means it will no longer accelerate and the drop rate will remain constant. The final speed of a face down skydiver is about 122 miles per hour.
Average Acceleration
Average acceleration is the total change in velocity divided by the total time. This can be found using the equation a = Δv ÷ Δt.
For example, if the speed of an object increases from 20 m/s to 50 m/s in 5 seconds, the average acceleration will be:
a = (50m/s – 20m/s) ÷ 5s
a = 30m/s ÷ 5s
a = 6m/s2
Deceleration or Negative Acceleration
When the speed of an object decreases (slows down) it is called deceleration. It can also be represented by a negative acceleration. This means that the direction or vector of the points of acceleration is opposite to the direction of motion of the object.
For example, if the speed of an object changes from 40 m/s to 10 m/s in a period of 2 seconds, then the average acceleration will be:
a = (10m/s – 40m/s) ÷ 2s
a = -30ms ÷ 2s
a = -15m/s2
This can also be referred to as a deceleration of 15 m/s2.