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Terminal Velocity Date ________ When objects are in free fall, the air resistance (__________ _________) is negligible and the only force on the falling object is the force of _____________________ which is _______________. In free fall, when two objects (one twice as massive as the other one) are dropped they fall with the same acceleration. Why? The object with twice the mass is attracted to the Earth with more force (2F). Doubling the force means _____________ the acceleration. Doubling the mass means ___________ the acceleration. The ratio of force to mass is the ______________. In free fall, the acceleration is _____________, _________________. 1 Nonfree Fall Air resistance cannot be ignored!!! When a rock is dropped in the air it accelerates because the weight of the rock (Fg) (downward force) is greater than the force of air resistance (R) (upward force). There is a net force downward so the rock _____________________ downward. As the speed of the rock increases, there is greater number of air molecules that the object moves through each second. The force of air resistance (upward force) gets greater and greater. There is still a net force downward so the rock ______________________ downward. 2 As the rock gains speed eventually the force of air resistance increases until the air resistance (upward force) equals the weight of the falling object (downward force). Now the net force is _________________ and the acceleration is _____________. The object has reached _____________ __________. The downward force of gravity is _________ in magnitude but ______________________ in direction to the upward force of air resistance. 3 4 Terminal velocity when jumping out of a helicopter The person has a mass of 100 kg. So Fg = mg = 100 kg x 9.8 m/s2 = 980 N As the person falls, the R = 0 N air resistance, R changes. a = Fnet = Fg = 980 N m The air resistance is in the upward direction so it is positive. R = 490 N a = Fnet = The force of gravity on the person Fg = 980 N m is always downward so it is negative. R = 980 N a = Fnet = m When the air resistance __________ the force of gravity on the person there is _________ acceleration and the person has reached ___________ ____________ Fg = 980 N R = 1470 N a = Fnet = m Fg = 980 N R = 1960 N a = Fnet = m Fg = 980 N When the parachute is expanded fully the force of air resistance upward equals the weight, Fg, of the person. ______________ ____________ has been reached again. R = 980 N a = Fnet = m Fg = 980 N 5 Terminal velocity when jumping out of a helicopter What happens if the mass of the person is doubled? This person has a mass of 200 kg. So Fg = mg = 200 kg x 9.8 m/s2 = 1960 N R = 0 N Fg = 1960 N a = Fnet = m a = Fnet = m Fg = 1960 N R = 490 N a = Fnet = Fg = 1960 N m R = 980 N R = 1960 N a = Fnet = m Fg = 1960 N Why does is take longer for a more massive person to reach terminal velocity? Terminal velocity depends on ________________ and ________________ ______________ of the object that is falling. 6 Two smooth balls of the exact same size are dropped from a high building. One ball is made of wood and the other is made of iron. Which ball encounters the greater force of air resistance? a) wooden ball b) iron ball c)...both the same Why? 7 As this daring Physics student falls faster and faster through the air her acceleration... a) increases b) decreases c) remains the same 8 Graphs of Falling Objects (The object is moving away from the frame of reference.) Object does not reach terminal velocity Object reaches terminal velocity 9