1. What Is Acceleration?
Acceleration tells us how quickly the velocity of an object changes with time. If an object speeds up, slows down, or changes direction, it is accelerating.
Even if the speed stays the same but the direction changes, there is still acceleration.
1.1. Acceleration as Rate of Change of Velocity
Velocity can increase or decrease. Acceleration measures how fast this change happens.
It is a vector quantity because it depends on the change in velocity, which also has direction.
1.2. Everyday Meaning
When a car starts moving faster, you feel pushed backward. That feeling is due to acceleration.
When a moving vehicle slows down, it is also experiencing acceleration—specifically negative acceleration.
2. Formula for Acceleration
The basic formula for acceleration is:
\( a = \dfrac{v - u}{t} \)
where:
- \( u \) = initial velocity
- \( v \) = final velocity
- \( t \) = time taken for the change
2.1. Example Calculation
If a bike increases its velocity from 5 m/s to 15 m/s in 5 seconds:
\( a = \dfrac{15 - 5}{5} = 2 \, \text{m/s}^2 \)
This means the bike's velocity increases by 2 m/s every second.
2.2. Units of Acceleration
Acceleration is measured in:
- meters per second squared (m/s²)
This unit shows how much the velocity changes per second, every second.
3. Types of Acceleration
Acceleration can take different forms depending on how velocity changes.
3.1. Positive Acceleration
Velocity increases with time. Example: A car speeding up after a signal turns green.
3.2. Negative Acceleration
Velocity decreases with time. This is also called deceleration or retardation. Example: Applying brakes while driving.
3.3. Zero Acceleration
Velocity remains constant. Even if the object is moving, there is no acceleration when the speed and direction do not change.
4. Acceleration in Everyday Life
We witness acceleration all the time without thinking about the physics behind it.
4.1. Examples
- A train picking up speed after leaving a station.
- A ball rolling down a slope and gaining speed.
- A runner starting slow and then sprinting.
- A car stopping at a traffic light (negative acceleration).
5. Uniform and Non-Uniform Acceleration
Acceleration can be constant or can change over time.
5.1. Uniform Acceleration
Acceleration remains the same throughout the motion. Example: An object freely falling under gravity (ignoring air resistance) has uniform acceleration of \( 9.8 \, \text{m/s}^2 \).
5.2. Non-Uniform Acceleration
Acceleration keeps changing. Example: A car moving in heavy traffic, where the speed increases and decreases irregularly.