 Gravity is the force of attraction between two objects due to their masses  Acceleration is the rate at which velocity (speed with a direction) changes over time  All objects accelerate towards Earth at a rate of 9.8 meters per second per second (m/s 2 )

 Air Resistance : the force that opposes the motion of objects through air › Depends on size, shape, and speed

 Terminal Velocity : objects fall at constant velocity, force of gravity is balanced by air resistance  How does a parachute affect air resistance?

 Free fall : when gravity is pulling an object down and no other forces are acting on it  Why are astronauts in a space shuttle always falling? (page 39/40)

 Orbiting objects are in free fall  Centripetal Force : unbalanced force that causes objects to move in a circular path › Two motions cause orbiting ( circular path )  Traveling around an object  Falling

 Projectile Motion : the curved path that an object follows when thrown or propelled near the Earth’s surface due to gravity. › Frog Leaping › Sprinkler › Diver › Ball being thrown

 Two components › Horizontal motion › Vertical motion  Horizontal Motion

 Two components › Horizontal motion › Vertical motion  Vertical Motion (GRAVITY)

 v = g x t  Using this equation you can calculate the change in velocity of a falling object  Practice: A stone at rest is dropped from a cliff, and the stone hits the ground after a time of 3 seconds. What is the stone’s velocity when it hits the ground?

1. A penny at rest is dropped from the top of a tall stairwell. What is the penny’s velocity after it has fallen for 2 seconds? 2. The same penny hits the ground in 4.5 seconds. What is the penny’s velocity as it hits the ground? 3. A marble at rest is dropped from a tall building. The marble hits the ground with a velocity of 98 m/s. How long was the marble in the air? 4. An acorn at rest falls from an oak tree. The acorn hits the ground with a velocity of 14.7 m/s. How long did it take the acorn to land?