C H A P T E R 4 Forces and Newton's Laws of Motion

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C H A P T E R   4Forces and Newton's Laws of
Motion
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4.5 Newton's Third Law of Motion
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4.5 Newton's Third Law of Motion
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4.5 Newton's Third Law of Motion
Whenever one body exerts a force on a second
body, the second body exerts an oppositely
directed force of equal magnitude on the first
body.
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 Examples of Newton's 3rd Law
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Example 4
Suppose that the mass of the spacecraft in Figure
4.7 is mS 11 000 kg and that the mass of the
astronaut is mA 92 kg. In addition, assume that
the astronaut exerts a force of P 36 N on the
spacecraft. Find the accelerations of the
spacecraft and the astronaut.
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Example 4
Suppose that the mass of the spacecraft in Figure
4.7 is mS 11 000 kg and that the mass of the
astronaut is mA 92 kg. In addition, assume that
the astronaut exerts a force of P 36 N on the
spacecraft. Find the accelerations of the
spacecraft and the astronaut.
Astronauts use a tether to stay connected to the
space capsule.
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Application of Newton's Third Law
Some rental trailers include an automatic
brake-actuating mechanism.
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4.6 Types of Forces

• In nature there are two general types of forces,
  fundamental and non-fundamental.
• Fundamental forces
• Gravitational force
• Strong nuclear force
• Weak nuclear force-----
• Electromagnetic force--!Electroweak force
• Non-fundamental forces
• Pushing, Pulling, Kicking, Grabbing, etc.
• These are related to the electromagnetic force.
  They arise from the interactions between the
  electrically charged particles that comprise
  atoms and molecules.

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Fundamental Forces
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Unification of Fundamental Forces
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Newtons Law of Universal Gravitation
Every body in the universe attracts every other
body with a force that is directly proportional
to the product of the masses of the bodies and
inversely proportional to the square of the
distance between the bodies.
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Newtons Law of Universal Gravitation
Every body in the universe attracts every other
body with a force that is directly proportional
to the product of the masses of the bodies and
inversely proportional to the square of the
distance between the bodies.
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Universal Gravitational Constant
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Universal Gravitational Constant
The proportionality constant, G is called the
universal gravitational constant. Its value in
the SI system of units is,G 6.67 ?
10-11N.m2/Kg2.
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Universal Gravitational Constant
The proportionality constant, G is called the
universal gravitational constant. Its value in
the SI system of units is,G 6.67 ?
10-11N.m2/Kg2. The law of gravitation is
universal and very fundamental. It can be used to
understand the motions of planets and moons,
determine the surface gravity of planets, and the
orbital motion of artificial satellites around
the Earth.
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Acceleration Due to Gravity
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Acceleration Due to Gravity
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Acceleration Due to Gravity
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Acceleration Due to Gravity
Calculate g for planet Earth at sea level.
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Weight
Weight Mass x Gravity
The weight of an object is the gravitational
force that the planet exerts on the object. The
weight always acts downward, toward the center of
the planet. SI Unit of Weight newton (N)
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The Hubble Space Telescope
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Example 6
The mass of the Hubble Space Telescope is 11 600
kg. Determine the weight of the telescope (a)
when it was resting on the earth and (b) as it is
in its orbit 598 km above the earth's surface.
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4.8 The Normal Force
The normal force FN is one component of the force
that a surface exerts on an object with which it
is in contact, namely, the component that is
perpendicular to the surface.
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Normal Force Is Not Always Equal to the Weight
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Elevator Ride
What happens to your weight during an elevator
ride?
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Apparent Weight
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Apparent Weight