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1. LAWS OF
MOTION

2. CONTENTS

3. CONSERVATION OF
MOMENTUM
• For an isolated system in the absence of an external force the
total momentum remains unchanged
i) Conservation Of Angular Momentum
• According to the law of conservation of angular momentum for
a closed system the angular momentum always remains
constant until and unless there is no external torque acting on
the system.
EXAMPLE
• During skating if the skater folds his or her hands then he is
able to rotate at a greater speed as compared to when he
opens his hands wide. This is on account of conservation of
angular momentum.

4. ii) Conservation Of Linear Momentum
• All the bodies have the power of exerting a
force on other bodies that are in their line of
motion. The magnitude or quantity that
measures this capacity of the bodies is called
linear momentum.
• The law of conservation of linear momentum
states that the momentum will remain constant
no matter what, until and unless, any external
force comes into action.

5. Conservation of Momentum Examples
• When atoms collide with each other the law of
conservation of momentum is followed.
• When the bullet hits the wooden block the law of
conservation of momentum is followed and the block
rises to a particular height.
• When two cars hit each other in an accident then the
law of conservation of momentum is followed.
• When a baseball is hit by the bat the law of
conservation of momentum is followed.
• When two runners collide in a race then the law is
followed.
• Two billiard balls colliding with each other.

6. BILLIARD BALL

7. Friction
Suppose you decide to ride a skateboard.
You push off the ground and start moving.
According to Newton’s First Law of
Motion, if no other forces are acting on
your skateboard, you will continue to
move….BUT
What happens?

8. Friction
Your skateboard slows down because of
friction.
Friction is the force that opposes motion
between two surfaces that are touching each
other.
The amount of friction depends on two things:
Kind of surface.
Forces pressing the surfaces together.

9. What Causes Friction?
Even though a surface may look smooth, if you
magnify the surface it isn’t smooth.
Everything is made of molecules. The molecules
come together to make bumps. Some
surfaces have molecules that leave large
bumps and some leave smaller bumps, but
all surfaces have bumps.
Microwelds occur when two bumpy surfaces
are rubbed up against each other they stick
together.

10. Static Friction
Suppose your little brother gets into a box and wants
you to move him. He is too heavy to lift.
You try to push the box and it doesn’t move.
What type of acceleration does it have?
Remember Newton’s Second Law of Motion
If the acceleration is zero, the net force is zero.
Therefore, because you can’t move it, another force is being
applied to cancel out your force.
That opposing force is friction caused by the microwelds
between the bottom of the box and the floor.
This type of friction is called static friction.

11. Sliding Friction
To help you move your little brother, you
decide to ask a friend.
You both push and slowly, but not easily, the
box starts to slide across the floor.
When you stop pushing, it quickly stops
moving.
Sliding the box is difficult and there is still
resistance.
Although you have overcome the
microwelds, there is still a sliding friction
occurring.

12. Sliding Friction
Sliding Friction is the force that opposes
the motion of two surfaces sliding past
each other.
Sliding friction is caused by microwelds
constantly breaking and then forming
again as the box slides along the floor.
To keep the box moving, you must
continually apply a force to overcome
sliding friction.

13. Rolling Friction
Have you ever seen a car stuck in the snow.
Every time the driver steps on the gas, the
tires just spin and the car doesn’t go
anywhere?
This is because there isn’t enough friction
between the slippery ground and the tires.
How could you create more friction to get the
tires to move the car?
Drop sand, gravel, put a board under each of
the front tires.

14. Rolling Friction
The friction between the rolling tires and
the ground is called rolling friction.
Rolling friction works partly because of
microwelds.
Rolling friction is much less friction than
static or sliding friction.

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