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Gravity and Motion All objects fall with the same acceleration Galileo proposed that all objects will land at the same time when they are dropped at the same time from the same height. Acceleration due to gravity is the same for all objects All objects accelerate toward Earth at a rate of 9.8 m/s/s. Air resistance slows down acceleration Air resistance occurs between the surface of the falling and the air that surrounds it Air resistance affects some objects more than others Depends on size and shape Acceleration stops at terminal velocity Terminal velocity – objects that fall at a constant velocity Ex: Sky diver and a parachute Free fall occurs when there is no air resistance Free fall – gravity is pulling it down and no other forces are acting on it Because of air resistance (fluid friction) free fall can occur where there is no air – in a vacuum (a place in which there is no matter) or in space Orbiting objects are in free fall It is impossible to be “weightless” anywhere in the universe Weight is a measure of gravity, and it acts on all matter, and everything is made of matter Astronauts “float” in orbiting spaceships because of free fall Two motions combine to cause orbiting An object is said to be orbiting when it is traveling in a circular or nearly circular path around another object Moving forward and always falling The role of gravity in orbiting Any object in circular motion is constantly changing direction Centripetal force – the unbalanced force that causes objects to move in a circular path Gravity provides the centripetal force that keeps objects in orbit Projectile motion and gravity Projectile motion – the curved path an object follows when thrown or propelled near the surface of the Earth Two components Horizontal motion: The forward motion of the object Vertical motion: the gravitational pull of earth