# Velocity and Acceleration

### What is Velocity?

Although velocity and speed are often used interchangeably by students, they are not the same thing. As a student, you will need an understanding on motion and speed to better comprehend velocity and acceleration.

The direction in which an object is moving is what differentiates velocity from speed.

Velocity can be defined as speed in a given direction. It is also be defined as the rate of change of displacement.

• Velocity = Change in distance/Change in time

Meanwhile, recall that velocity is a vector quantity since it has both magnitude and direction.

Below is a narrative that differentiates speed from velocity:

A bus is moving on a highway at a speed of 100 meters per 20 seconds. If the bus changes its direction and moves at a different speed (or even the same speed), then that's velocity.

With regards to the above instance, the bus may move at a velocity of 100m/20s in the northern direction and 100m/20s in the eastern direction.

Always remember that speed and velocity both have the same Standard International (SI) unit; and that is meter per second (m/s).

### Acceleration

The velocity of a moving object can either decrease or increase over a period of time; and this is where acceleration comes into play. Consider the instance below:

When you ride a bicycle, you start slowly but as soon as you increase the push on the pedals, the bicycle moves faster (accelerate). When you stop pushing the pedals, the bicycle begins to move slowly (negative acceleration).

From the above instance, we can therefore say that acceleration may also be negative.

Note: Deceleration is an English term used to describe negative acceleration; but in physics, we use the term 'acceleration' to denote both the positive and negative changes in velocity.

Acceleration is defined as the rate of change of velocity. Acceleration is also defined as the measurement of how much the velocity of an object changes with time.

• Acceleration = Change in velocity/Change in time

If an object changes velocity after a fixed amount of time, then such acceleration is said to be constant (that is: constant acceleration). Consider the instance below:

• If we throw a table tennis ball down a slope, it will roll downwards more rapidly at each second.

• On the 1st second, let's assume it's velocity to be 20m/s.

• On the 2nd second, its velocity becomes 25m/s.

• On the 3rd second, it becomes 30m/s.

With regards to the above velocities, such ball is said to have a constant acceleration of 5m/s.

This means that: for every 5 meters moved, the tennis ball accelerates by 1 second.

We also have the concept of average acceleration in motion.

Average acceleration is the total change in velocity over a period of time, divided by the duration of that period.

Acceleration is a vector quantity and its SI unit is meter per second (m/s) or meter per second square (m/s2). 