Falling and Air Resistance Reading Guide Answers Chapter 6.7

Falling and Air Resistance 1. The accelerations of the feather and coin in a vacuum (no air) are the same. This would be no different on the moon, because the Moon has no air resistance. However, since the moon has less gravity, they would both fall slower than on Earth. 2. As the air resistance increases, the net force will decrease. (or as the air resistance decreases, the net force will increase)

Falling and Air Resistance 3. The net force of an object in free fall is equal to the weight of the object (air resistance is not considered in free fall) 4. Air resistance is dependent upon –A.speed –B.frontal area: exposed surface area 5.Air resistance can be reduced by –A.reducing speed –B.reducing frontal area (exposed surface area)

Falling and Air Resistance 6.The elephant would experience more air resistance because the elephant has a much larger frontal area exposed to air. The elephant catches more air!

Terminal Velocity 1.Terminal speed is the maximum speed that a falling object will reach; it occurs when the acceleration and net force equal zero. Terminal velocity differs only by the addition of direction of motion (down!) 2.Weight (gravitational force) and air resistance balance at terminal velocity. 4.A feather reaches terminal velocity so quickly because its frontal area is very large compared to its very small weight.

5.Terminal velocity for a skydiver ranges from 150 to 200 km/h. (124 mph) 6.Zero acceleration means that the object is no longer accelerating; zero velocity means the object is at rest. 7.Terminal speed changes if the frontal area exposed to the air changes (variations in body orientation). If the skydiver reduces frontal area, the terminal speed would increase. If the skydiver increases the frontal area, the terminal speed would decrease.

8.Terminal velocity for a skydiver with the parachute deployed ranges from 15 to 25 km/h. 9.As the baseball and tennis ball fall, their speeds will increase and the air resistance builds. Since the weight of the tennis ball is less than the baseball, the net force on the tennis ball decreases more quickly than the net force on the baseball. This causes the falling tennis ball to be accelerated at a progressively lower rate than the falling baseball.