1. Chapter 6 Forces and Motion
Section 1 Gravity and Motion
pages 150 to 157

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

5. Falling Objects All objects accelerate at a rate of 9.8m/s2 (g)
For every second an object falls, the objects downward velocity increases by 9.8m/s
Δv= g•t
Δv= the change in velocity
g=the acceleration due to gravity (9.8m/s/s)
t=time

6. Falling Objects Acceleration stops at the terminal velocity.
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. It then falls at a constant velocity which is called terminal velocity.

7. Air Resistance
Air resistance is fluid friction that opposes the motion of objects through the air. It slows down the acceleration of falling objects.
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

8. FREE FALL
Free fall only happens if gravity is the only force acting on an object.
It can only occur where there is no air (in a vacuum or in outer space).
Free fall is acceleration due to gravity

9. FREE FALL
Although astronauts appear weightless in space, they are not. There is still some gravity. There is no air in space.
This is due to free fall and orbiting in space

10. FREE FALL
Sky divers are NOT in free fall because air resistance is always acting on them.

11. Orbiting 2 motions combine to cause orbiting
A forward motion and free fall toward earth
Orbiting objects are in free fall.

12. 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

13. Projectile Motion
Projectile motion is the curved path an object follows when thrown or propelled near the surface of the earth.
It has 2 components- a vertical motion and horizontal motion. Gravity only affects the vertical motion of projectile motion.