Chapter 2-2: Forces and Motion

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Chapter 2-2 Forces and Motion

• Gravity and Motion

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Effects of Gravity on Matter

• Gravity a force of _____________ between
  objects that is due to their masses
• Gravity can affect the position of an object or
  the direction of the objects motion.
• All __________, because it has mass, is affected
  by gravity.

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Size of Earths Gravitational Force

• Earth has a ______ mass in comparison to all
  other objects around you.
• Earth has a ________ gravitational force.

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Newton and Gravity

• Law of Universal Gravitation all objects in the
  universe attract each other through gravitational
  force. The size of the force depends on the
  ____________ of the objects and the ___________
  between them.
• As mass increases, gravitational force increases.

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Weight

• Weight a measure of the gravitational force on
  an object changes with position
• Mass the amount of matter in an object
• If an object has more mass, then gravitational
  force is larger and they weigh more.
• Where do you weigh more, on Earth or on the moon?

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Units of Weight and Mass

• Weight is a force so it is measured in
  __________.
• Mass is measured in _________ or kilograms

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Galileo
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Gravity and Acceleration

• The acceleration on Earth due to gravity is the
  same for _______ objects.
• Acceleration depends on both _________ and
  _________.
• Heavier objects experience more gravity but they
  have more inertia, so they are more difficult to
  accelerate.

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Acceleration Due To Gravity

• Acceleration is the rate at which velocity
  changes.
• All objects accelerate toward Earth at a rate of
  9.8 m/s2.
• For every second an object falls, its velocity
  increases by 9.8 m/s.
• In the 1st second, a falling objects velocity is
  9.8 m/s. In the 2nd second, it is traveling at a
  rate of 19.6 m/s.

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Velocity of Falling Objects

• The following equation is used to find the change
  in velocity (?v)
• ?v gravity time
• Try the practice problems in the Math Focus
  section on page 151.

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Air Resistance

• Air resistance is the force that opposes the
  motion of objects through the air.
• The amount of air resistance depends on the size,
  shape, and speed of the object.
• The larger the __________ ________ of an object,
  the more air resistance acting on it.
• How do parachutes help sky divers land safely?
• They increase air resistance and slow the sky
  divers to a safe terminal velocity.

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Acceleration and Terminal Velocity

• When the upward force of air resistance balances
  the downward force of gravity, the object stops
  accelerating.
• The object then falls at a constant velocity
  called terminal velocity.
• The terminal velocity of a human without a
  parachute is about 120 miles per hour.

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Free Fall with no Air Resistance

• An object is in free fall if gravity is pulling
  it down and no other forces are acting on it.
• Free fall can occur in a vacuum (a place where
  there is no matter) or in space.
• Weightlessness is when objects are in a state of
  free fall. Astronauts float in orbiting
  spacecrafts because they are in a state of free
  fall. They have a sensation of weightlessness.

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Orbiting Objects

• Two motions combine to cause orbiting motion
  forward due to inertia and downward (free fall)
  due to gravity.
• The moon stays in orbit around Earth because of
  the moons forward motion and Earths
  gravitational pull.
• The unbalanced force that causes orbiting objects
  to move in a circular path is centripetal force.
• Centripetal means center seeking.

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Projectile Motion and Gravity

• Projectile motion the curved path an object
  follows when it is thrown or propelled near the
  surface of the Earth.
• Projectile motion has two components horizontal
  motion and vertical motion, which are independent
  of each other.

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Projectiles

• Gravity does not effect the horizontal motion of
  a projectile.
• When you throw a ball, the horizontal velocity is
  constant.
• Gravity does have an effect on the vertical
  motion of a projectile.
• Gravity causes the vertical velocity to increase.