Lecture 8 Newton and Gravity

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Lecture 8Newton and Gravity
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Isaac Newton (1642-1727)

• Laws of Motion
• Law of Gravity

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Isaac Newton (1642-1727)

• Born the year Galileo died.
• Quiet, studied at Cambridge, returning home
  during outbreak of the plague.
• Invented calculus

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Definitions

• Velocity speed and direction
• Acceleration a change in velocity
• change in speed and/or direction
• Mass measure of how much matter is present
• Weight the force of gravity on an object

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Newtons First Law Law of Inertia

• A body at rest remains at rest OR
• A body in motion moves in a straight line at a
  constant speed.
• UNLESS acted upon by an outside force.
• Example pushing book across table, friction
  causes it to stop, little friction in space.

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Newtons Second Law

• The acceleration of an object is proportional to
  the force acting on it.

F Force mmass aacceleration

• The larger the force, the faster the velocity
  increases or decreases or the direction changes.
• Need more force to accelerate massive objects

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Newtons Third Law

• Whenever a body exerts a force on another body,
  the second body exerts and equal and opposite
  force on the first body.

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Newtons Law of Gravitation

• There is an attractive force between all objects
  with mass.
• Force decreases with distance.
• But, the force is never zero!

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Gravity Formula
constant

• G is a constant
• M1 and M2 are the masses of the two objects
• D is the distance
• If mass increases, force increases
• If distance increases, force decreases

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Gravitation
constant

• Force decreases rapidly with distance

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Orbits of Bodies

• Balance between force of gravity and inertia of
  planet

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Shapes of Orbits

• If velocity is too low, object will fall to the
  ground (A, B C)
• If at exactly correct velocity circular orbit
  (E)
• If slightly too slow or fast, elliptical orbit

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What does weightless mean?

• Astronauts appear to have no weight

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Weightlessness

• Shuttle and astronaut both falling
  (accelerating) toward the Earth at the same rate
  free fall
• Shuttle does not exert pressure on astronaut
• Although the Earth does exert force on astronaut,
  there is no additional force relative to the
  shuttle