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## Newton's Three Laws of Motion

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### Newton's Three Laws of Motion by BUENO OLIVIER Isaac Newton (1642-1727) Life & Character Born at Woolsthorpe in Lincolnshire (England) entered Cambridge University in ... – PowerPoint PPT presentation

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Title: Newton's Three Laws of Motion

1
Newton's Three Lawsof Motion
• by
• BUENO OLIVIER

2
Isaac Newton (1642-1727)
• Life Character
• Born at Woolsthorpe in Lincolnshire (England)
• entered Cambridge University in 1661
• Professor of Mathematics in 1669 and Natural
Philosopher
• President of the Royal Society of London in 1703
until death.

3
Scientific achievements
• OPTICS
• discovered measurable, mathematical patterns in
the phenomenon of color, found white light as
mixture of infinitely varied colored rays,book
Opticks (1692).
• MATHEMATICS
• discovered general methods of resolving problems
of curvature, embraced in his "method of
fluxions" and "inverse method of
fluxions",..books Principia I and II (1687)

4
Scientific achievements
• GRAVITATION
• calculated the relative masses of heavenly bodies
from their gravitational forces, calculated the
force needed to hold the Moon in its orbit book
Principia I and III (1687)
• MECHANICS
• calculated the centripetal force needed to hold a
stone in a sling, and the relation between the
length of a pendulum and the time of its swing
book Principia I (1687)

5
Newtons First law of motion
• Also known as law of inertia,
• States,
• An object will remain at rest, or uniform motion
in a straight line, with the same speed and in
the same direction unless acted upon by an
unbalanced force.

6
Newtons First law of motion
• Comments
• This means that if you leave a book on a bench
over night, when you return in the morning,
unless an outside force moved it, it will be in
the same place

No external forces applied-gt the book remains at
rest
7
Newtons First law of motion
• Comments Examples
• But what is an unbalanced force? first consider a
book at rest on a bench. There are two forces
acting upon the book. - the Earth's
gravitational force, and the push of the bench on
the book (sometimes referred to as a Fn). Since
these two forces are of equal magnitude and in
opposite directions, they balance each other. The
book is said to be at equilibrium.

The bench pushes upward on the book
Gravity pulls downward on the book
8
Newtons First law of motion
• Comments Examples
• Consider another example of a balanced force.
There are two forces acting upon this person The
force of gravity and the force of the floor.
these two forces are equal magnitude and in
opposite directions, The person is at equilibrium.

The floor pushes upward on the person
Gravity pulls downward on the person
9
Newtons First law of motion Involving Friction
• Comments Examples
• Now consider a book sliding from right to left
across a bench. Sometime in the prior history of
the book, it may have been given a shove. The
force of gravity and the force of the bench on
the book balance each other. Yet there is no
force present to balance the force of friction.
As the book moves to the left, friction acts to
the right to slow the book down. There is an
unbalanced force. The book is not at equilibrium
and subsequently accelerates

The bench pushes upward on the book
Force of friction between the bench/book
Gravity pulls downward on the book
10
Newtons First law of motion Involving Friction
• Lets exercise
• Consider that the book weighs 0.2 kg. As it
slides across the bench with a constant velocity,
its coefficient of friction is 0.15. What force
must be exerted on the book, so that it maintains
its constant velocity? (go to the next slide for
the answer)

Fn
Fob ?
Ffr
Fg
11
Newtons First law of motion Involving Friction
• Answer explanations
• We know that the magnitude of the force of
gravity is mg. We recognize that the two object
in contact are in relative motion (kinetic
friction Ffr µkFn).
• Solving with the y-direction equation gives Fn
mg, and solving for the x-direction, F µkmg)
• The force that must be used on the book is F
µkmg (0.2)(0.15)(9.80 m/s) 0.294 N

12
Newtons First law of motion
• Comments Examples
• Considering a soccer ball in the middle of a
field with no external forces exerted (kicking,
moving, high winds,) on it.

Normal force of the ground on the ball
No external forces
Force of gravity on the ball
13
Newtons First Law of Motion
The floor pushes upward on the person
• Comments Examples
• If you kick the soccer ball, it will continue
moving until it hits something.Newtons First Law
of Motion

Fn
Fg
Gravity pulls downward on the person
14
Newtons First Law of Motion
The floor pushes upward on the person
• Comments Examples
• Your foot can only interact with the ball through
forces of contact (there is a gravitational force
between your foot and the ball, but it is so tiny
that it is completely negligible), so once the
ball is not in contact with your foot, it no
longer exerts any force on the ball.

Fn
Force of contact between the foot and the ball
Fg
Gravity pulls downward on the person
15
Newtons First law of motion involving Friction
• Comments Examples
• Once the ball is not in contact with the foot,
the only object interacting with the ball is the
ground. The ball will eventually stop even if it
does not hit a wall (the friction between the
ball and the ground, and between the ball and the
air)Newtons First law of motion

Fn
Fn
Fg
Friction between the ball and the air
Ffr
Fg
16
Newtons First law of motion
• Comments Examples
• We feel the effects of Newton's First Law every
day, but usually don't notice them because other
forces interfere. If it was not for other forces
we will be in constant motion.

17
Newtons First law of motion
• Comments Examples
• On earth, the atmosphere will eventually slow
down all moving objects, but in a vacuum
(basically an empty space with no air or
atmosphere), like space, it will be more obvious
that objects obey Newton's Laws.

Direction of the force due to the reactors
Friction between the wind and the plane
Direction of the force from the reactors
Fg
18
Newtons First law of motion
• Comments Examples
• In space, the First Law is much more obvious.
Objects will follow their natural trajectories
until they are stopped by an outside force.

19
Newtons First law of motion
• Comments Examples
• One of the most common places people feel the
First Law is in a fast moving vehicle, such as a
car or a bus, that comes to a stop. An outside
force stops the vehicle, but the passengers, who
have been moving at a high speed, are not stopped
and continue to move at the same speed

20
Newtons First law of motion
• Comments Examples
• If the car hits a cement road divider it is
stopped (outside force). The crash dummy, however
is not so lucky. Since he is not wearing a seat
belt, and is not connected to the car, he will
continue to move at 60 mph, flying out through
the front windshield.

21
Newtons First Law of Motion
• Comments Examples
• The dummy will fly through the air until he hits
the ground. This is because the earth's gravity
stopped him from moving any further. If this
collision had happened in zero-g, in a vacuum,
the dummy would theoretically keep on hurtling
away from the car at 60 mph.

22
Newtons Second law of motion
• States,
• The acceleration of an object is directly
proportional to the net force acting on it and is
inversely proportional to its mass.
• The direction of the acceleration is in the
direction of the net force acting on the object

23
Newtons Second law of motion
• shortened gt SF ma
• where f is a push or pull that gives energy to an
object the motion of the object. a is the rate of
change of velocity.

24
Newtons Second law of motion
Heavy mass, needs more force
• Comment Example
• Newton's Second Law is more abstract than the
first. The greater the mass, the greater the
amount of force needed to accelerate the object.

Small mass, needs less force
25
Newtons Second law of motion
• Example
• Betty is developing her muscles by pushing this
car that weighs 1500 kg. She makes it go 0.02
m/s/s. Using Newton's Second Law, can you compute
how much force I applied to the car? (the answer
in the next slide)

Not really who you expect to push the car !!!
Force exerted by the ground on the car
F mass car x g
26
Newtons Second law of motion
Fn
30 Newton applied
Fg
• Comments Examples
• Betty has not really move that much consider she
has only exerted 30 Newton of force. (FMA, so
you plug in the data and get F 1500kg x .02
m/s/s. This comes out to 30 kg m/s/s, which is
equal to 30 Newton.

27
Newtons Second law of motion
• Example
• Here Betty is trying to do the impossible. She
wants to push this 2500 kg van to a gas station.
She computes 125 Newton on the car. How fast will
she make it go?

Shes trying hard !!!
Force exerted by the ground on the car
125 N
A ?
F 2500 x g
28
Newtons Second law of motion
Fn
125 N
0.05 m/s/s
Fg
• Answer Explanations
• It may seem impossible but Betty will make it go
0.5 m/s/s. Because using Newton's Second Law, we
found that (FMA, gt AF/M. So you plug in the
data and get A 125/2500kg. This comes out to
0.05 m/s/s.

29
Newtons Third law of motion
• Comments
• Anytime an object exerts a force on another
object, the second object exerts an equal and
opposite force on the first.

30
Newtons Third law of motion
• Comments
• Newton's Third Law is probably the most famous of
his laws.
• The Third Law at first seems simple, but is a
very important law.
• Every time we interact with our surroundings we
feel the Third Law.

31
Newtons Third law of motion
• Comments Examples
• If use the convention that F means the force on
object A from object B, then Newton's third law
can be written
• FAB - FBA

Object A
Object B
32
Newtons Third law of motion
• Comments Examples
• When you punch someone in his face your hand not
only applies a force to the person's face, the
person's face applies a force to your hand.

Force exerted on his face by the punch
Force exerted on the hand by his face
33
Newtons Third law of motion
• Comments Examples
• The magnitude of the force on each body is
identical and the forces on the on the two bodies
are in the opposite directions to each other.

Ffp
-Fpf
34
Newtons Third law of motion
• Comments Examples
• The only reason why a rocket is able to launch,
is that when its engine pushes out the gases, the
gases exert an equal and opposite force back on
the rocket, which accelerate.

Force exerted on the rocket by the engine
Force exerted on the engine by the rocket
35
Newtons Third law of motion
• Comments Examples
• One of the most unnoticeable Newtons third law,
is when we walk.
• We can walk forward because, when one foot pushes
backward against the ground, the ground pushes
forward on that foot.

Force exerted on her foot by the floor
Force exerted on the floor by her foot
36
Newtons Third law of motion
The floor pushes upward on the person
• Comments Examples
• Newton first law still applying in this case.
• Her mass has also in influence on her walking.

Force exerted on her foot by the floor
Force exerted on the floor by her foot
Gravity pulls downward on the person
37
Newtons Third law of motion
• Comments Examples
• Even in the most unthinkable moment, we do exert
Newtons third law.
• We cannot be touched without being touched

38
The End
• presented
• by
• BUENO OLIVIER
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