Gravity and Motion

1
Chapter 6

• Gravity and Motion

2
Aristotle

• Believed the rate at which an object falls
  depends on the mass
• So if you dropped a baseball and a marble from
  the same height, he thought the baseball would
  land first

3
Galileo

• Questioned this idea
• According to legend he dropped 2 cannon balls
  with different masses from the Leaning Tower of
  Pisa
• They landed at the same time
• This changed the understanding of gravity and
  falling objects.

4

• Objects fall to the ground at the same rate
  because the acceleration due to gravity is the
  same for all objects

5

• All objects accelerate at a rate of 9.8m/s2
• For every second an object falls, the objects
  downward velocity increases by 9.8m/s
• ?v gt
• ?v the change in velocity
• gthe acceleration due to gravity
• ttime

6

• As long as the net force on a falling object is
  not zero, the object accelerates downward
• As the object falls, the upward force of air
  resistance continues to increase until it matches
  the downward force of gravity .
• When this happens the net force is zero and the
  object stops accelerating.

7
Terminal velocity

• When an object falls at a constant velocity.

8
Terminal Velocity
9
Air Resistance

• Fluid friction opposes the motion of objects
  through the air
• Amount of air resistance on an object depends on
  the size and shape
• Because air is all around us, any falling object
  is affected by air resistance

10
FREE FALL

• Acceleration due to gravity
• Although astronauts appear weightless in space,
  they are not.
• This is due to free fall and orbiting in space
• 2 motions combine to cause orbiting
• A forward motion and free fall toward earth

11
Orbiting

• A circular or near circular path around another
  object.
• This means it is also constantly changing
  direction.
• Since it is changing direction an unbalanced
  force is acting on it
• This force is centripetal force
• Gravity provides this force

12
Projectile Motion

• Projectile motion-is the curved path an object
  follows when thrown or propelled near the surface
  of the earth.
• Has 2 components-vertical and horizontal.