2. Sir Isaac Newton was an English scientistSir Isaac Newton was an English scientist
and mathematician famous for hisand mathematician famous for his
discovery of the law of gravity alsodiscovery of the law of gravity also
discovered the threediscovered the three laws of motionlaws of motion.He.He
was born in the year 1643 on january 4was born in the year 1643 on january 4thth
and expired on march 31th, 1727.and expired on march 31th, 1727. HeHe
published about laws of motion & laws ofpublished about laws of motion & laws of
gravity in his bookgravity in his book PhilosophiaePhilosophiae
Naturalis Principia MathematicaNaturalis Principia Mathematica inin
1687.1687. Today these laws are known asToday these laws are known as
Newton’s Laws of MotionNewton’s Laws of Motion..
INTRODUCTION OFINTRODUCTION OF
NEWTONNEWTON
3. Newton’s Laws ofNewton’s Laws of
MotionMotion
11stst
LawLaw – An object at rest will– An object at rest will
stay at rest, and an object instay at rest, and an object in
motion will stay in motion atmotion will stay in motion at
constant velocity, unless actedconstant velocity, unless acted
upon by an unbalanced force.upon by an unbalanced force.
22ndnd
LawLaw –– Force equals massForce equals mass
times acceleration.times acceleration.
33rdrd
LawLaw –– For every action thereFor every action there
is an equal and oppositeis an equal and opposite
reactionreaction..
4. Newton’s First LawNewton’s First Law
An object at rest tends to stay at restAn object at rest tends to stay at rest
and an object in motion tends to stay inand an object in motion tends to stay in
motion unless acted upon by anmotion unless acted upon by an
unbalanced force.unbalanced force.
5. WWhat does this mean?hat does this mean?
Basically, an object will “keep doingBasically, an object will “keep doing
what it was doing” unless acted onwhat it was doing” unless acted on
by an unbalanced force.by an unbalanced force.
If the object was sitting still, it willIf the object was sitting still, it will
remain stationaryremain stationary. If it was. If it was
moving at a constant velocity, it willmoving at a constant velocity, it will
keep movingkeep moving..
It takesIt takes forceforce to change the motion ofto change the motion of
an object.an object.
6. 11stst
LawLaw
Inertia is theInertia is the
tendency of antendency of an
object to resistobject to resist
changes in itschanges in its
velocity:velocity:
whether inwhether in
motion ormotion or
motionless.motionless.
These pumpkins will not move unless acted on
by an unbalanced force.
7. Some Examples from RealSome Examples from Real
LifeLife
Two teams are playing tug of war. They are bothTwo teams are playing tug of war. They are both
exerting equal force on the rope in oppositeexerting equal force on the rope in opposite
directions. This balanced force results in nodirections. This balanced force results in no
change of motion.change of motion.
A soccer ball is sitting at rest. It
takes an unbalanced force of a kick
to change its motion.
8. Newton’s Second LawNewton’s Second Law
Force equals mass times acceleration.Force equals mass times acceleration.
F = maF = ma
Acceleration: a measurement of how quickly an
object is changing speed.
9. If mass remains constant, doubling the acceleration,
doubles the force. If force remains constant, doubling
the mass, halves the acceleration.
10. What does F = ma mean?What does F = ma mean?
Force isForce is directly proportionaldirectly proportional to mass and acceleration.to mass and acceleration.
Imagine a ball of a certain mass moving at a certainImagine a ball of a certain mass moving at a certain
acceleration. This ball has a certain force.acceleration. This ball has a certain force.
Now imagine we make the ball twice as big (double the
mass) but keep the acceleration constant. F = ma says
that this new ball has twice the force of the old ball.
Now imagine the original ball moving at twice the
original acceleration. F = ma says that the ball will
again have twice the force of the ball at the original
acceleration.
11. Newton’s Third LawNewton’s Third Law
For every action there is an equal andFor every action there is an equal and
opposite reaction.opposite reaction.
12. What does this mean?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 with equal force. This is why you are
not moving. There is a balanced force acting on
you– gravity pulling down, your seat pushing up.
13. 33rdrd
LawLaw
There are two forcesThere are two forces
resulting from thisresulting from this
interaction - a force oninteraction - a force on
the chair and a force onthe chair and a force on
your body. These twoyour body. These two
forces are calledforces are called actionaction
andand reactionreaction forces.forces.
14. 33rdrd
LawLaw
The reaction of a rocket isThe reaction of a rocket is
an application of the thirdan application of the third
law of motion. Variouslaw of motion. Various
fuels are burned in thefuels are burned in the
engine, producing hotengine, producing hot
gases.gases.
The hot gases push againstThe hot gases push against
the inside tube of the rocketthe inside tube of the rocket
and escape out the bottomand escape out the bottom
of the tube. As the gasesof the tube. As the gases
move downward, the rocketmove downward, the rocket
moves in the oppositemoves in the opposite
direction.direction.
15. VocabularyVocabulary
Inertia:
the tendency of an object to resist changes
in its state of motion
Acceleration:
•a change in velocity
•a measurement of how quickly an object is
changing speed, direction or both
Velocity:
The rate of change of a position along
a straight line with respect to time
Force:
strength or energy
