Acceleration is the rate of change in velocity. In other words if a body changes its speed or dirction then it is said to be accelerated.

**Acceleration**

**Acceleration (a)**

Acceleration is the rate of change
in velocity. In other words if a body changes its speed or dirction then it is
said to be accelerated.

Acceleration = change in velocity/
time = [final velocity (v) â€“ intial velocity (u) ] / time (t)

a = (vâ€“u) / t

SI unit of acceleration is m/s^{2}

In other words, the object undergoes
acceleration when its speed and/or direction change(s).

The velocity at different times of a
train departing direction is given in the figure. Analyse this and complete the
table .

__Answer:__

Analysis:

When the train covers the distance A to B and B to C, it is
accelerated motion.

When it covers the distance C-D, there is no acceleration (i.e)
uniform velocity.

When it covers the distance D to E and E to F it has negative acceleration or deceleration or retardation, (i.e.) Its velocity decreases with respect to time.

** **

**Tell me**

A car at rest starts to travel in a
straight path. It reaches a velocity of 12 m/s in 4 s . What is its
acceleration. Assuming that it accelerates uniformly?

Initial velocity u =0 m/s (since the car starts from rest)

Final velocity (v) =12 m /s

Time taken (t ) =4 s

acceleration ( a ) =(v â€“ u) / t

= (12â€“0)/4

=3 m / s^{2}

**See how brisk I am !**

My name is cheetah. I can run at a great speed. Do you know
what my speed is? 25 m/s to 30 m/s. My speed changes from 0 to 20 m/s in 2
second. See how good my acceleration is !

Acceleration of the cheetah = [ Final velocity(v) - Initial
velocity(u) ] / [time taken]

= [ *v - u* ] / t = 20-0
/ 2 = 20/2 = 10 m/s^{2}

Acceleration of the cheetah = 10 m/s^{2}

^{}

**Tell me**

From the above information, can you
calculate the acceleration of the cheetah?

** **

**Positive acceleration**

If the velocity of an object
increases with respect to time, then the object is said to be in positive
acceleration or just acceleration.

** **

**Negative acceleration or deceleration or retardation**

If the velocity of an object
decreases with respect to time, then the object is said to be in negative
acceleration or deceleration or retardation.

The velocity of a golf ball rolling
in a straight line changes from 8 m/s to 2 m/s in 10 s. What is its
deceleration, assuming that it is decelerating uniformly ?

Initial velocity (u) =8 m/s

Final velocity (v) =2 m/s

Time taken(t) =10 s

Acceleration (a) =(v â€“ u)/t

=(2 â€“ 8)/10

= â€“0.6 m/s^{2}

The deceleration is â€“0.6 m/s^{2}

**Uniform acceleration**

An object undergoes uniform
acceleration when the change (increase or decrease) in its velocity for every
unit of time is the same.

Table shows a moving bus with
uniform acceleration.

When the velocity of the object is
increasing by 20 m/s the acceleration is 20 m/s^{2} When the velocity of the object is decreasing
by 20 m/s the deceleration is 20 m/s^{2}.

When the velocity of the object is decreasing by 20m/s the
deceleration is 20 m/s2.

Deceleration = Decrease in velocity / Deceleration = t = 20/20 =
1s

The velocity of the object is decreasing by 20m/s in one second.

**Non â€“ uniform acceleration**

An object undergoes non uniform
acceleration if the change in its velocity for every unit of time is not the
same.

Note that the change in velocity is
not the same for every second. The moving object is undergoing non uniform
acceleration.

Tags : Force and Motion | Term 1 Unit 2 | 7th Science , 7th Science : Term 1 Unit 2 : Force and Motion

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7th Science : Term 1 Unit 2 : Force and Motion : Acceleration | Force and Motion | Term 1 Unit 2 | 7th Science

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