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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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