Newton's First Law of Motion: I. Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it. This we recognize as essentially Galileo's concept of inertia, and this is often termed simply the "Law of Inertia".

1. LAWS OF MOTION

2. What causes the motion ?
Why does the speed of an object change
with time ?
Do all motion require a cause ?
If so what is the nature of this cause ?

3. Sir Isaac Newton (1643-1727) an English scientist
andmathematician famous for his discovery of
the law of gravity also discoveredthe three laws
of motion. He publishedthemin his book
Philosophiae Naturalism PrincipiaMathematica
(mathematic principles of natural philosophy) in
1687. Today these laws are known as Newton’s
Laws of Motion anddescribe the motion of all
objects on the scale we experience in our
everyday lives.
Sir IsaacNewton

4. WHAT IS THE LAW OF MOTION ?
Newton's laws of motion are three
physical laws which provide
relationships between the forces
acting on a body and the motion of
the body.

5. Force
Force is an action that can change motion . A force is
what we call a push or a pull, or any action that has the
ability to change an object’s motion. Forces can be used
to increase the speed of an object, decrease the speed of
an object, or change the direction in which an object is
moving.

6. BALANCED & UNBALANCED FORCES
If the forces on an object are equal and opposite,
they are said to be balanced, and the object
experiences no change in motion.
If they are not equal and opposite, then the forces
are unbalanced and the motion of the object
changes.

7. FIRST LAW OF MOTION
An object at rest tends to stay at rest and object in motion tends
to stay in motion unless actedupon by an unbalancedforce.
What does this mean ?
Basically, an object will keep doing what it was doing, unless
actedon by an unbalancedforce.
If the object was sitting still, it will remain stationary. If it was
moving at a constant velocity, it will keep moving.
It takes force to change the motion of an object.

8. NEWTON’S FIRSTLAWOF MOTIONALSOCALLED
LAWOF INERTIA
INERTIA: the tendency of an object to resist
changes in its state of motion
The First Law states that all objects have inertia.
The more mass an object has, the more inertia it
has (and the harder it is to change its motion).

10. More Examples from Real Life
A powerful locomotive begins to pull a long line
of boxcars that were sitting at rest. Since the
boxcars are so massive, they havea great deal
of inertia and it takes a large force to change
their motion. Once they are moving, it takes a
large force to stop them.
On your way to school, a bug flies into
your windshield. Since the bug is so
small, it has verylittle inertia and
exerts a verysmall force on your car
(so small that youdon’t even feel it).

11. Newton’s 1st Law and You
Don’t let this be you. Wear seat belts.
Because of inertia, objects (including you) resist changes in
theirmotion. When a car going on 80 km/hour is stopped
by the brick wall, your body still keeps on movingat 80
km/hour.

12. NEWTON’S SECOND LAW OF MOTION
FORCE EQUALS MASS TIME ACCLERATION
F= ma
Acceleration: a measurement of how quickly
an object is changing speed.
Force is directly proportional to mass and
acceleration.

13. WHAT DOES F=ma MEAN ?
F = ma basically means that the force of an object comes
from its mass and its acceleration.
Something very massive (high mass) that’s changing speed
very slowly (low acceleration),like a glacier, can still have
great force.
Something very small (low mass) that’s changing
speed very quickly (high acceleration), like a bullet,
can still have a great force.

14. If We increase theamount of net
force than the acceleration also
increases in the same amount. If we
decreasethe net force than
acceleration also decreases.

15. In the Picture given we double the force than the magnitude
of acceleration also becomes double. On the contrary we
decrease the force then, acceleration also decreases. We
understand the relation between force and acceleration.
Well, do you think mass affects the acceleration? Suppose
that you push a box that is empty, you can easily push it. If
the box is full, then can you push it easily with the same
force? The answer is of course “NO”. Bigger mass results in
bigger force. Thus, we find another relation of force which
is:
Net force ~ mass

16. Force is directly proportional to mass and acceleration.
If the mass is constant, when we increase the force the
object gains acceleration with the same amount or, if the
force is constant, when we decrease the mass
acceleration increases with the same amount. Therefore:
Net Force ~ acceleration
Net Force ~ mass
F=ma
Net Force ~ mass x acceleration

17. NEWTON’S THIRD LAWOF MOTION
For every action there is an equal and opposite reaction
What does this mean?
For every force acting on an object, there is an equal force
acting in the opposite direction. Right now, gravity is
pulling you down in your seat, but Newton’s Third Law says
your seat is pushing up against you withequal force. This is
why you are not moving. There isa balancedforce acting on
you–gravity pulling down, your seat pushing up.

19. EXAMPLES
The astronauts working on the space station have a serious
problemwhen they needto move aroundin space: There is
nothing to push on. The solution is to throwsomething
opposite the direction you want to move. This works because
all forces always come in pairs.

20. The reaction of a rocket is an
application of the third law of
motion. Various fuels are burned in
the engine, producing hot gases.
The hot gases push against the
inside tube of the rocket and escape
out the bottomof the tube. As the
gases move downward, the rocket
moves in the opposite direction.

21. Helicopters – blades push air
down. Air pushes chopper up.
Lift – upwardreaction force
When lift equals weight of
chopper, it can hover
When lift is greater. Thus the
chopperrises.

22. 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).

23. Flying gracefully through the
air, birds depend on Newton’s
third law of motion. As the
birds push down on the air
with their wings, the air
pushes their wings up and
gives them lift.

24. Measuring Weight
When you standon a scale, your
weight pushes down on the scale.
This causes the scale pointer to point
to your weight.
At the same time, by Newton’s third
law the scale pushes up on you
witha force equal to your weight.
This force balances the downward
pull of gravity on you.

25. Free Fall and Weightlessness
Now suppose you were standing on
a scale in an elevator that is
falling.
A falling object is in free fall when
the only force acting on the force
is gravity.
You and the scale are bothin
free fall.

26. Because the only force acting on you
is gravity, the scale no longer is
pushing up on you.
According to Newton’s thirdlaw, you
no longer push down on the scale.
So the scale pointer stays at zero
and you seem to be weightless.
Weightlessness is the condition that
occurs in free fall when the weight
of an object seems to be zero.

27. AGNES RICHARD
IX –B
ROLLNO. 29
THANK YOU