Physics Class 9[Motion] PArt=2

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5. acceleration

• Acceleration is a measure of the change in the velocity of an object per unit time. 
  
• If the velocity of an object changes from an initial value u to the final value v in time t, the acceleration a is given by,
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  $a=\frac{v-u}{t}$
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•  Uniform Acceleration =If it travels in a straight line and its velocity increases by equal amount in equal intervals of time. 
• Example =freely falling bodies, motion of ball rolling down the inclined plane etc.
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•  Non Uniform Acceleration =If its velocity increases or decreases by unequal amount in equal intervals of time.
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• If acceleration is in the direction of the velocity then it is positive acceleration.
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• If it is in the direction opposite to the direction of velocity then it is negative and the negative acceleration is termed retardation.
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• SI unit of acceleration is ms^-2.

Concept Map of Acceleration

Fill in the blanks
1.Speed
2. SI
3. time
4. Velocity
5. Displacement
6. direction
7. Motion
8. Direction
True and False Statement
1. False
2. True
3. True
4. True
5. false
6. false
7. false

6. Equations of uniformly accelerated motion

• There are three equations of bodies moving with uniform acceleration which we can use to solve problems of motion==

First Equation of motion

• The first equation of motion is $v=u+at$ ,
•  Where= v is the final velocity 
•     u is the initial velocity of the body.
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• NOTE--First equation of motion gives velocity acquired by body at any time $t$.
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• Now we know that acceleration
  

Second Equation of motion

• Second equation of motion is
  $s=ut+\frac{1}{2}a{t}^2$
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Where =$u$ is initial velocity, 
• $a$ is uniform acceleration 
•  $s$ is the distance traveled by body in time $t$.
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• NOTE=Second equation of motion gives distance traveled by a moving body in time $t$.

Third equation of motion

• Third equation of motion is
  $v^2=u^2+2as$
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Where= $u$ is initial velocity,
•  $v$ is the final velocity,
•        $a$ is uniform acceleration    
•  $s$ is the distance travelled by the body.
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• NOTE=This equation gives the velocity acquired by the body in traveling a distance $s$.
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• These three equations of motion are used to solve uniformly accelerated motion problems and following three important points should be remembered while solving problems.
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  1. if a body starts moving from rest its initial velocity $u=0$
  2. if a body comes to rest i.e., it stops then its final velocity would be $v=0$
  3. If a body moves with uniform velocity then its acceleration would be zero.