Lesson 5 : Free Fall and the Acceleration of Gravity

Introduction to Free Fall

A free-falling object is an object which is falling under the sole influence of gravity. Thus, any object which is moving and being acted upon only by the force of gravity is said to be "in a state of free fall." This definition of free fall leads to two important characteristics about a free-falling object:

• Free-falling objects do not encounter air resistance.
• All free-falling objects (on Earth) accelerate downwards at a rate of approximately 10 m/s/s (to be exact, 9.8 m/s/s).

Because free-falling objects are accelerating downwards at a rate of 10 m/s/s (9.8 m/s/s – to be more accurate), a ticker tape trace of its motion depicts an acceleration.

The diagram at the right shows such a ticker tape trace. The position of the free-falling object at regular time intervals, every 0.1 second, is shown. The fact that the distance which the ball travels every interval of time is increasing is a sure sign that the ball is speeding up as it falls downward. Recall from Lesson 1, that if an object travels downward and speeds up, then its acceleration is directed downward.

This free-fall acceleration can also be demonstrated using a strobe light and a stream of dripping water. If water dripping from a medicine dropper is illuminated with a strobe light and the strobe light is adjusted such that the stream of water is illuminated at a regular rate – say every 0.2 seconds; instead of seeing a stream of water free-falling from the medicine dropper, you will see several consecutive drops. These drops will not be equally spaced apart; instead the spacing increases with the time of fall (as shown in the diagram above), a fact which serves to illustrate the nature of free-fall acceleration.

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