Newton

1
Newtons Laws of Motion

• Chapter 3 Chapter 4

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Newtons First Law of MotionInertia

• The first law of motion states that an object at
  rest will remain at rest and an object in motion
  will remain in motion unless acted upon by an
  unbalanced force.

3
Inertia

• Newton called the tendency of objects to
  remain in motion or to stay at rest inertia.
• EXAMPLE
• A car moving in a turn and the passenger
  presses against the door because he is still
  moving in a straight line. A car moves, you fall
  backwards. It stops, you fall forwards. Your
  body has inertia.

4
Question

• Which would have greater inertia? A toy car or a
  real car? Why would there be a difference?

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Answer

• The more mass an object has, the greater its
  inertia is.
• A much greater force would be needed to change
  the real cars velocity.

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History of Inertia

• Aristotle (384 - 322 B.C.) Believed that the
  natural motion of celestial objects was
  circular, while terrestrial objects tend to
  naturally fall. He also believed that object
  need force to maintain motion

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History of Inertia

• Galileo (1564 - 1642) Claimed that no force was
  needed to keep an object in uniform,
  straight-line motion forever. It is the force of
  friction that slows an object down.

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History of Inertia

• Newton (1642 - 1727) During the years of 1665
  and 1666, Isaac Newton developed three laws that
  describe the states of motion. He also created
  the mathematical equations needed to solve them.
  Newton was moved by his family away from Oxford
  to avoid the Black Death also known as the
  plague. The significance of his contribution was
  perhaps best expressed by the Apollo crew as they
  were hurtling towards the moon. They radioed a
  message to mission control saying We would
  like to thank the person who made this trip
  possible...Sir Isaac Newton!

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Friction

• Chapter 5

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Friction A Force Opposing Motion

• Friction is a force that acts in a direction
  opposite to the motion of the moving object.
• Friction will cause a moving object to slow down
  and finally stop.

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Sliding Friction

• When solid objects slide over each other, the
  type of friction that results is sliding
  friction.
• EXAMPLE
• moving a box across the surface of a table.

12
Rolling Friction

• The friction produced by objects such as wheels
  or ball bearing is called rolling friction.
  Rolling friction tends to be less than sliding
  friction.
• EXAMPLE
• roller blades, bikes, and cars.

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Fluid Friction

• Fluid friction is usually less than sliding
  friction. Water and air are considered fluids.
  The force exerted by fluid is called fluid
  friction.
• EXAMPLE
• air resistance to a falling object and a boat
  moving through the water.

14
Lubricants

• Slippery fluids like grease, reducing friction.

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Newtons Second Law of Motion Force mass x
acceleration
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Newtons Second Law of Motion

• This law explains how force and acceleration are
  related.
• Newtons second law of motion show how force,
  mass, and acceleration are related. No force, no
  motion!

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Physicist like Aristotle of Greece, Sir Isaac
Newton (he was responsible for totally
understanding gravity) and Galileo have conducted
experiments on gravity. Legend has it that in
the late 1500s, the famous Italian scientist
Galileo dropped two cannonballs at exactly the
same time from the top of the Leaning Tower of
Pisa in Italy. According to the scientific
theories of the day, the more massive ball should
have landed first. But Galileo wanted to
disprove this theory. His hypothesis was that
all object fall at the same rate no matter what
their masses are. Galileos experiment displays
the basic laws of nature that govern the motion
of falling objects.
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Formula

• Force Mass x Acceleration
• (N) (kg) (m/sec2)
• 1N 1 kg x 1 m/sec2

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Formula

• Fma Force
• aF/m Acceleration
• mF/a Mass

F
m
a
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Classwork Practice Problems

• 1. 66 kg x 1 m/sec2
• 2. 1000 kg x 9.8 m/sec2
• 3. If a 60 kg person on a 15 kg sled is pushed
• with a force of 300 N, what will be the
  persons acceleration?
• 4. A bowling ball rolled with a force of 15 N
  accelerates at a rate of 3 m/sec2 a second ball
  rolled with the same force accelerates 4 m/sec2.
  What are the masses of the two balls?

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Falling Objects

• The acceleration of a falling object is due to
  the force of gravity between the object and the
  Earth.
• Near the surface of the Earth, the acceleration
  due to the force of gravity (g) is 9.8 m / sec2

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Gravitational Forces of Common Objects

• Moon 1/6 the Earths gravity
• Saturn 95 times the Earths gravity
• Sun 330,000 times the Earths gravity

23
Air Resistance

• Experiments
• 1. Air pressure and inertia breaks a pencil.
• 2. Galileos famous cannonball experiment.

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Terminal Velocity

• When a falling body no longer accelerates. It
  has reached terminal velocity. Sky divers reach
  terminal velocity at about 190 km / hr. At this
  point, the sky divers no longer feel the
  sensation of falling.

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Newtons Third Law of MotionAction Reaction
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Newtons 3rd Law of Motion

• The third law of motion states that for every
  action, there is an equal and opposite reaction.
  In short, for every force there must be an equal
  opposite force. All forces come in pairs.
• The reaction engine of rockets is an excellent
  application of the third law of motion. The
  fuels push against the sides of the rocket and
  escapes out of the bottom. The gases move
  downward and the rocket will move in the opposite
  direction, or upward.

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Discussion and Practice

• Turn to page 110 and look at figure 4-16. Which
  of Newtons three laws of motion explains why
  they jumper lands in the water, not the dock?

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Summary of Newtons Laws of Motion