# Concept of Acceleration

*Running race*

Children’s day was nearing and all the students were very excited to play games and win prizes. It was the first day of the games and it was a running race. The race track was ready and pintu was also participating together with his best friend Bunty. Both of them were preparing for this race for a very long time.

The whistle was blown and everyone started running. Pintu was not looking at anyone else and was running as fast as he can. Bunty was running ahead of everyone on the race and was looking back, again and again, to compare and make sure where he was. The finish line was getting closer and pintu still did not look at anyone else but himself. He started running faster every second and soon he was ahead of Bunty and also won the race.

*THINK:*

- how did pintu run faster and faster as the finish line was nearing?

We can see that as everyone was running towards the finish line, every student had their own velocity.

Pintu won the race because he was running faster every second. Which means he was increasing his velocity.

This changing (increasing/decreasing) of the velocity of a body is called **acceleration.**

## ACCELERATION

What is Acceleration?

**Acceleration is the measure of the change in the velocity of a moving object.**

When riding a bicycle, if you pedal faster, the cycle moves faster. The cycle is accelerating. When the accelerator of a car is pressed down then the car velocity increases, which means the car is accelerating.

**FORMULA:**

Acceleration of a body is equal to the change in velocity of the body divided by change in time.

If v_{2} is the final velocity and v_{1} is the starting velocity of a car then the acceleration of car is

Acceleration= (v_{2}-v_{1})/(t_{2}-t_{1})

Example:

**A bike is moving with 30 m/s velocity in the beginning and 50 m/s velocity in the end. The time between the starting and the end is 20 seconds. What is the acceleration of the bike?**

Answer)

Acceleration= (end velocity – starting velocity)/(20 seconds)

= (50-30)/(20)

= 20/20

= 1 m/s^{2 }

This is the acceleration of the bike.

A body is said to be accelerating even though its velocity is decreasing.

### GRAVITATIONAL ACCELERATION:

Whenever you throw a ball high into the air, it comes down and falls on the ground. It falls because of gravity.

When you throw the ball very high you can observe that when it is coming down due to gravity, its velocity is increasing.

**Why does the velocity of a falling body increases?**

Because gravity is exerting a pulling force on the body which increases the velocity of the body. And this increase in velocity because of gravity is called * GRAVITATIONAL ACCELERATION*.

Every object that falls from the above the ground experiences gravitational acceleration. And this gravitational acceleration is also a reason why all the objects stay on the ground and don’t fly away.

## QUIZ

1 ) What does acceleration measure?

- The change in velocity
- The change in the shape
- The change in time
- The change in gravity

2 ) A car is slowing down as it reaches a point. Is it accelerating? ( )

- True
- False

3 ) The final velocity of a cycle is 20 m/s and the starting velocity is 5 m/s. If the time between starting and end is 5 seconds. What is the acceleration of the cycle?

- 8 m/s
^{2 } - 35 m/s
^{2 } - 3 m/s
^{2 } - 1 m/s
^{2 }

4 ) Why does a falling body increase its velocity while falling?

- Due to air
- Due to its weight
- The velocity does not increase
- Due to gravitational acceleration

5 ) The units of acceleration are?

- Newtons
- M/s
^{2 } - M/s
- No units

## Responses