Uniform Circular Motion and Gravitation

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Uniform Circular Motion and Gravitation
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UCM

• What is UCM?
• It describes an object that moves in a circle
  with a constant speed
• Implications of UCM
• An object accelerates without changing its speed.
• The direction continuously changes as an object
  moves around a circle

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UCM

• Newtons first law says that an object in motion
  continues in motion with a constant velocity
  unless acted upon by a net external force.
• Velocity is a vector, speed and direction.
• A constant velocity means constant speed AND
  direction.
• Direction changes, therefore a force was applied!

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UCM

• An objects natural path is a straight line,
  therefore to pull an object out of its natural
  path a net force was applied
• What is this force?
• This force could be any of our everyday forces
  (weight, normal, tension, applied, or friction)
  or a combination of those five.
• It is the force or forces that maintain(s) the
  circle
• Does this force have a name?
• The Centripetal Force (center seeking), Fc

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UCM

• If there is a net force, is there an
  acceleration?
• Of course, SF ma after all!
• Does this acceleration have a name?
• The Centripetal Acceleration, ac

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UCM

• What about direction?
• The force and acceleration have the same
  direction, F and a, but what is it?
• Check out the proof on the board
• Towards the CENTER of the circle

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UCM

• What is the equation for acceleration?

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UCM

• What is the equation for centripetal force?
• Remember that Fc is the net force toward the
  center of the circle.

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Examples of Fc
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Examples of Fc
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Examples of Fc
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Examples of Fc
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Examples of Fc
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Centripetal vs Centrifugal

• The centrifugal force is a fictional force. It
  is not real! It is usually used in place of the
  correct Newtons First Law when explaining
  certain behaviors exhibited in circular motion.
• Watch and Listen to Mr.James
• Go forth and enlighten those that unknowingly
  spread incorrect physics.

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Newtons Law of Universal Gravitation

• Every particle in the universe attracts every
  other particle in the universe with a force that
  is proportional to the product of the masses and
  inversely proportional to the square of the
  distances between them. The force acts along the
  line joining the two points.

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Newtons Law of Universal Gravitation
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Gravity Strength on Earth
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Graviton

• http//en.wikipedia.org/wiki/Graviton

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Satellites and weightlessness

• Two types of weightlessness
• Apparent free fall
• Real Away from all massive bodies
• Satellites orbit because of the gravitational
  force

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Johannes Kepler

• 1571 1630
• Assistant to Tycho Brahe (1546 1601) from 1599
  1601
• Replaced Copernicus circular orbits with
  ellipses (25 years of calculating to do this)
• http//www-astronomy.mps.ohio-state.edu/pogge/Ast
  161/Unit3/watershed.html