Prepared By: Shakil Raiman
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First Law: If there is no unbalance force – a stationary object will
remain stationary and a moving object will keep on moving at a
constant speed in a straight line.
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Second Law: The unbalanced force is directly proportional to the rate
of change of momentum. Direction of the change in momentum is
same as the direction of unbalanced force.
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Third Law: To every action force there is an equal and opposite
reaction force.
Only unbalanced force can cause the acceleration.
In the formula,
F = ma ,
F = unbalanced force ,
m = mass of an object
a = acceleration
 In the formula,
F – f = ma
F = applied force
f = opposing forces ( friction or air resistance)
Therefore, F – f = unbalanced force
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Weight W = mg
Friction is a contact force.
Friction always decreases the efficiency of any engine.
Friction always decreases the speed of a moving car that
means it works as opposing force to the motion.
 Advantages and Disadvantages of friction are given below:
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Advantages
Disadvantages
to hold an object
reduces the efficiency of
any engines
for the movement of any
car or animal
tear or wear the moving
parts (tyres of car)
Negative effect of friction can be reduced by:
 Making the surface smooth
 Lubricating
 Using ball bearings.
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Friction is less in wet surface.
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As friction is less in wet surface the breaking distance will
be more.
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In wet surface deceleration decreases.
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Distance travelled during thinking is known as thinking distance.
 Thinking distance is affected by drivers reaction time and speed of the car.
 If the driver is drunk, sleepy or tired the thinking time increases So the thinking
distance increases
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Distance travelled after the brake is applied.
 Braking distance depends on the speed, road condition, and tire or brake
condition.
 Braking distance increases if the speed increases,
 if the road is wet or icy, there is less grip or friction so braking distance
increases,
 if the tire is old, there is less grip or friction. So braking distance increases
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Stopping Distance = Thinking distance + Braking distance
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Initially only weight acts downward. So,
object accelerates downward.
As the speed of the object increases, air
resistance increases.
So, unbalance force decreases.
So, acceleration decreases.
At a point, air resistance becomes equal to
the weight.
Unbalanced force become zero.
So no acceleration occurs. Object reaches
terminal (constant final) velocity.
drag force
depends on shape
of the falling
objects.
 If the smooth or
streamlined the
drag force will be
less.
 Parachute
increases the air
drag (resistance)
very much and
reduces terminal
speed.
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Wish you all very good luck and excellent
result.