PHYSICName : Norhasnida Bt Abd. RahmanUnit : PPISMP Sains Semester 1Lecturer : Miss Roshidah Binti Mat

Newton’s Laws Of Motion

NEWTON’S FIRST LAWS

Laws of inertia. Inertia-tendency of an object to resist changes in its

velocity.

CONCEPTS OF INERTIA

If an object is at rest, it tends to stay in that position unless some forces puts that object into motion, inertia makes the moving object continue to move at a constant speed in the same direction unless some external force changes the object's motion.

There are two parts to this statement - one which predicts the behavior of stationary objects and the other which predicts the behavior of moving objects. The two parts are summarized in the following diagram:

1st laws

SituationWhen the cardbord covering the glass is pulled out quickly, the coin resting on the

cardboard drops into the glass.The inertia of the coin maintains it in its original position even

when the cardboard is withdrawn.

Passenger in moving bus lurch forward when the bus comes to a halt suddenly.

The passenger were in a state of motion when the bus was

moving. When the bus stopped suddenly, the inertia in the

passengers made them maintain their state of motion. Thus when

the bus came to a halt, the passengers move forward.

ApplicationThe head of a hammer is secured tightly to its handle by knocking one end of the handle, held vertically, on a hard surface.

The hammer head to continue on its downwards motion when the

handle has been stopped, so that the top end of the handle is

slotted deeper into the hammer head.

Chilli sauce in a bottle is poured out quickly downward movement of the bottle

followed by a sudden stop.

The sauce in the bottles moves with the bottle during the

downward movement. When the bottle is stopped, the inertia of

the sauce causes it to continue in its downward movement and

thus the sauce is forced out of the bottle.

Inertia

Example

Explanation

Situation of Inertia

RELATIONSHIP BETWEEN MASS AND INERTIA

Two empty buckets which are hung with rope from a the ceiling.

One bucket is filled with sand while the other bucket is empty.

Then, both pails are pushed. It is found that the empty bucket is

easier to push compared to the bucket with sand.

The bucket filled with sand offers more resistance to movement.

When both buckets are oscillating and an attempt is made to stop them, the bucket filled with sand offers more resistance to the hand (more difficult to bring to a standstill once it has started moving)

This shows that the heavier bucket offers a greater resistance to change from its state of rest or from its state of motion.

An object with a larger mass has a larger inertia.

RELATIONSHIP BETWEEN MASS AND INERTIA

MASS = INERTIA

The LARGER the mass, the LARGER the inertia

RELATIONSHIP BETWEEN INERTIA AND SPEED

NERTIASPEED

INERTIA

The greater the speed the

greater the inertia

BalanceForce

When the forces acting on an object are balanced, they cancel each other out. The net force is zero.

.

The object at is at rest [velocity = 0]or moves at constant velocity [ a = 0]

Concept

Example

Concept

EffectEffect

Example

MOMENTUM

Momentum=Mass x velocity = mv

SI unit: kg ms-1

PRINCIPLE OF CONSERVATION OF MOMENTUM

EXTERNAL

FORCE

TOTAL MOMENTUMCONSTA

NT

In the absence of an external force, the total momentum of a system remains unchanged.

ELASTIC COLLISION

Momentum is

conserved

Both objects move independently at their

respective velocities after the collision.

Kinetic energy

is conserv

ed.

Total energy is conserved

Total Momentum Before = Total Momentum After

m1u1 + m2u2 = m1v1 + m2v2

INELASTIC COLLISION

Momentum is

conserved

Kinetic energy is not

conserved

Total energy is conserved

The two objects combine and move

together with a common velocity after

the collision.

Total Momentum Before = Total Momentum After

m1u1 + m2u2 = (m1 + m2) v

EXPLOSIONBefore explosion both object stick together and at rest. After collision, both object move at opposite direction.

Total Momentum before collision Is zero

Total Momentum after collision : m1v1 + m2v2

From the law of conservation of momentum: Total Momentum = Total Momentum Before collision after collision 0 = m1v1 + m2v2

m1v1 = - m2v2

-ve sign means opposite direction

EXAMPLE OF

EXPLOSION

NEWTON’S SECOND LAWS

concerned with the effect that unbalanced forces have on motion.

An unbalanced force acting on an object causes it to accelerate

UNBALANCED FORCE

ACCELERATION

The bigger the unbalanced force acting on the object the bigger the acceleration of the object.

RELATIONSHIP BETWEEN FORCE AND MASS

MASS FORCE

CONSTANT ACCELERATION

Relationship

between force, mass and

acceleration

a F m is constant

aF is constant

FORCE, MASS & ACCELERATION

The acceleration produced by a force on an object is directly

proportional to the magnitude of the net force applied and is inversely

proportional to the mass of the object. The direction of the

acceleration is the same as that of the net force .

When a net force, F, acts on a mass, m it causes an acceleration, a.

Effect of forces

Moves a stationary objectWhen a stationary toy car is pushed with

the hand, the toy car start to move.

Change the velocity of moving objectA toy car which is moving at a constant velocity accelerates when it is pulled using

an elastic string.

Slows down a moving objectWhen a vehicle move from a smooth surface to a rough surface, the force of

friction retards the motion of the vehicles

Stops the motion of an objectWhen a car collides with a wall, the car is

stopped by the wall.

Change the direction of motion When a tennis ball is hit by a racket, the reactive force causes the tennis ball to

change its direction.

Change the shape of an objectA straight ruler forms an arc when

bending forces are applied to both ends.

Example

Explanation

NEWTON’S THIRD LAWS

For every action, there is an equal and opposite reaction

CONCEPT OF NEWTON’S THIRD LAWS

According to Newton, whenever objects A and B interact with each other, they exert forces upon each other. When you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body.

Example Of

Newton’s Third Laws

When a person tries to jump from the boat to the jetty, his legs apply a force which pushes the boat backwards (the action). This action in turn produces a reaction force pushing him forward.

A swimmer uses his hands and legs to produces a forces which pushes the waterto the back of him. This action in turn produces a reaction pushing him forward in the water.

When a rifle is fired, the force propelling the bullet forward is the action. An opposite force is produced which pushes the rifle backwards; the reaction.

In rocket propulsion ,the exhaust gases are discharged in the form of a jet at the rear of the rocket. The downward-moving jet of gases reacts on the body of the rocket to create a reactive force in the opposite direction that drives the rocket upwards.

Newton's 3rd laws of motion :

Action and Reaction

NEWTON’S 3RD LAW IN NATURE

Consider the propulsion of a fish through the water. A fish uses its fins to push water backwards. In turn, the water reacts by pushing the fish forwards, propelling the fish through the water.

The size of the force on the water equals the size of the force on the fish; the direction of the force on the water (backwards) is opposite the direction of the force on the fish (forwards).

NEWTON’S LAWS CONCEPT MAP

SUMMARY

Newtons laws of motion

1st laws

Law of inertia

Inertia-tendency of an object to resist

changes in its velocity.

2nd laws

F=ma

3rd laws

Action=Reaction

Concepts of Newton's laws

1st laws

If an object is at rest, it tends to

stay in that position unless

some forces puts that object

into motion, inertia makes the moving

object continue to move at a

constant speed in the same

direction unless some external force changes the object's

motion.

2nd laws

When mass is in kilograms and acceleration is in m/s/s, the

unit of force is in newtons (N)

One newton is equal to the force

required to accelerate

one kilogram of mass at one meter/secon

d/second

3rd laws

Wherenever object A and B interact with

each other,they exerts forces upon each

other.There are two forces resulting from the

interaction - action forces and reaction

forces