Falling objects
bellringer If Wile E. Coyote and a boulder fall off a cliff at the same time, which do you think will hit the ground first?
objective Explain the effect of gravity and air resistance on falling objects Explain why objects in orbit are in free fall and appear to be weightless Describe how projectile motion is affected by gravity
misconceptions Heavier objects will fall faster than lighter objects Objects fall at a constant speed All objects have the same force of gravity http://www.youtube.com/watch?v=_mCC-68LyZM
Acceleration of gravity Galileo Galilei dropped items with different masses off the Leaning Tower of Pisa in Italy to prove that ALL OBJECTS FALL AT THE SAME RATE This happens because the acceleration of gravity – 9.8 m/s2 – is the same for all objects
Velocity of falling objects A falling object accelerates at a constant rate The object falls faster and farther each second than it did the second before You can calculate the change in velocity (Δv) of a falling object by using the following equation: Δv = g × t
Air resistance Air resistance is the force that opposes the motion of objects through air The amount of air resistance acting on an object depends on the size, shape, and speed of the object Notice mass is NOT a factor Objects with similar size, shape and speed but with different masses will fall at the same rate
Terminal velocity As the speed of a falling object increases, air resistance increases Eventually the upward force of air resistance continues is equal to the downward force of gravity The object then falls at a constant velocity called the terminal velocity
Free fall When the only force acting on an object is gravity, the object is in free fall Because air resistance is a force, free fall can occur only where there is no air Space http://www.youtube.com/watch?v=KDp1tiUsZw8 Vacuum http://www.youtube.com/watch?v=_XJcZ-KoL9o
orbiting An object is orbiting when it is traveling around another object in space When a spacecraft orbits Earth, it is moving forward But the spacecraft is also in free fall toward Earth The combination of these two motions causes orbiting
Centripetal force The unbalanced force that causes objects to move in a circular path is called a centripetal force Gravity provides the centripetal force that keeps objects in orbit
Projectile motion Projectile motion is the curved path an object follows when it is thrown or propelled near the surface of the Earth Examples: a frog leaping water sprayed by a sprinkler a swimmer diving into water balls being juggled an arrow shot by an archer
Horizontal vs. vertical motion Two motions combine to form the curved path: Horizontal Motion – a motion that is parallel to the ground The applied force (push or a pull) is usually the horizontal force Vertical Motion – motion that is perpendicular to the ground Gravity is usually the vertical force and it pulls the object down at an acceleration of 9.8 m/s2 This rate is the same for all falling objects