Thursday, December 14

# Acceleration Due to Gravity: It Will Blow Your Mind

Pretend you are standing on the roof of your school building. In your right hand is an egg, and in your left hand is a bowling ball. If you dropped, the two objects off the roof at the same time, which would hit the ground first— the egg, or the bowling ball?

The answer might not be what you think; the bowling ball and the egg would actually hit the ground at the same time! Why? Because the rate at which objects fall is the same no matter what an object weights.

The constant rate is called acceleration due to gravity and it is often represented by the letter ‘g.’ On Earth, at sea level, objects fall at a constant rate of 9.8 meters per second per second. So g= 9.8 m/s/s.

To calculate how fast a dropped object is going when it hits the ground, all you need to know is g and how long it took before the object hit the ground. Let us say you dropped that egg off the roof of your school, and, with a stopwatch, you measured that it took 5 seconds for the egg to splatter on the pavement. Here is how you would calculate the egg’s speed as it hit the ground:

Velocity= acceleration x time

Acceleration is equal to g, and it took the egg 5 seconds to hit the ground, so:

V= (9.8 m/s/s) x (5)

There you go!

According to legend, the renowned astronomer Galileo Galilei (1564-1642) used a strange experiment to discover that acceleration due to gravity was the same for all objects.

Prior to Galileo’s time most people believed (incorrectly) that heavy objects fall faster than lighter ones. That is what Aristotle had written thousands of years before, and people still accept it to be true! So Galileo, as the tale goes, dropped balls of different weights off the Leaning Tower of Pisa in Italy. So they hit the ground at the same time, Aristotle was proven wrong, and Galileo was proven correct.

Or so the story goes. Chances are this is actually just a story; the experiment probably never happened! That is not to say that Galileo did not help increase humanity’s knowledge of acceleration due to gravity, however, Galileo was not the first to postulate that falling objects accelerate independent of their mass, but he was the first to demonstrate that it was true with an experiment. He did it, though, not by dropping weights off the Leaning Tower, but by rolling balls of different masses down an inclined plane.

IN 1971, astronaut David Scott did his own version of the experiment. While on the moon, he dropped a hammer from one hand and a feather from the other. On Earth, this experiment would not exactly be fair, since air drag on the feather would make it flutter around rather than drop straight to the ground. However, in the vacuum of space, where there is no air (and hence, no air drag) the feather and hammer hit the ground at the same time!

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