4.2 Gravity

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4.2 Gravity
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Objectives

• Describe the gravitational force.
• Express the dependence of gravitational field on
  mass and distance, using proportions.
• Distinguish between mass and weight.

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Gravity

• The force of attraction that exists between all
  matter in the universe.
• Key word is matter
• Matter is the stuff you are and everything else
  is made of
• It takes a lot of mass for the gravity to be
  noticeable.
• Like planetary mass

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Law of Gravity

• The force of attraction between any two objects
  depends on their masses and the distances between
  them.
• The bigger the object, the more gravity it has
• The closer an object is to something the stronger
  the pull.

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4 Basic Forces

• Gravity
• Electromagnetic Force
• Causes electricity and magnetism
• Also causes chemical interactions between atoms
  and molecules
• Strong Nuclear Force
• Weak Nuclear Force
• Along with Strong Nuclear Force only act on
  particles in the nuclei of atoms

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Law of Universal Gravitation

• Formulated from Newtons data on motion of
  planets in 1687

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Law of Universal Gravitation

• G is a constant called the universal
  gravitational constant
• d is the distance between the two masses, m1 and
  m2.
• Enables us to calculate the force of gravity
  between any two objects if their masses and the
  distance between them is known.

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Range of Gravity

• Gravitys force depends on how close the object
  is to something.
• As an object gets further away, the force of
  gravity on that object decreases
• Inverse square law
• As the distance increases the gravity decreases
  exponentially

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Universal Gravitation

• Because it relates to all matter, on earth as
  well as the planets and stars
• Earths motion is affected by the gravitational
  pull of other planets
• 1846 astronomers used
• Law of Universal Gravitation
• to discover Neptune due to
• its pull on Uranus

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Gravitational Acceleration

• When all forces except gravity are ignored,
  falling object is in free fall
• All objects fall at same acceleration in free
  fall 9.8 m/s2
• By Newtons second law of motion, the force of
  Earths gravity on a falling object is the
  objects mass times the acceleration of gravity.
• Fmg

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Weight

• Gravitational force exerted on an object
• g Gravitational acceleration constant 9.8 m/s2

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Weight, Mass, and Gravity

• Mass
• How much matter you are made of
• Does not change depending location
• It is the same if you are on earth or in space or
  on the moon

• Weight
• The relationship between mass and gravity
• Changes depending on location
• Is different on earth and the moon and space

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Weight

• The table shows how various weights on Earth
  would be different on the Moon and some of the
  planets.

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In-Class Assignment