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

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

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.

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

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

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.

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

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

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

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

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

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

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.