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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when the cardboard is withdrawn.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