Sunday, 30 January 2011


Which will drop faster, a feather or a ball?

Turn the tube over and watch as the objects drop from one end to the other. Press the green button to suck air out of the tube. How do the objects fall now? To blow air back into the tube, press the red button.

In air, the feather will drop slower than the ball, whereas in the vacuum, they fall at the same rate.

The falling objects push the air out of their way, which creates drag, a force that opposes the falling motion, otherwise known as air resistance. The falling velocity of an object depends on the degree of air resistance in relation to the object’s weight. The feather will drop slower in air, because its air resistance in relation to its weight is significantly greater than that of the ball. In a vacuum, the falling velocity is only affected by the acceleration created by gravity, and this acceleration is the same for all objects. The ball and the feather will, therefore, fall at the same rate.

A falling object may achieve a velocity in which the air resistance is equal to the object’s weight. After this point, the falling velocity will no longer increase. This velocity is known as terminal velocity. Prior to the opening of the parachute, the terminal velocity of a skydiver is about 200 km/h in the normal face-down parachuting position, and as much as 300 km/h in an upright skydiving position.

The fastest momentary falling velocity measured for a human being is 1,142 km/h. The person started his jump from a helium balloon gondola that had risen 31 kilometres above the Earth's surface. The air resistance at that altitude is only 1/100 of the resistance at sea level.

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