# Back in ancient Greece, the philosopher Aristotle believed that solid objects fell because they were made up of the element earth and were trying to get.

## Presentation on theme: "Back in ancient Greece, the philosopher Aristotle believed that solid objects fell because they were made up of the element earth and were trying to get."— Presentation transcript:

Back in ancient Greece, the philosopher Aristotle believed that solid objects fell because they were made up of the element earth and were trying to get back under the air that was beneath them. He figured that heavier objects would fall faster than lighter objects. Galileo proved him wrong hundreds of years later by dropping two rocks of different sizes from a tall building Galileo found that the two rocks hit at the same time, disproving Aristotle.

Later, Isaac Newton discovered the Law of Universal Gravitation that explained Galileos results. Newton found that Gravity acts on all objects on earth in the same way. This means that ALL objects in free-fall will fall the same way. Newton Also discovered that objects actually accelerate as they fall

All objects fall with the same acceleration on earth It has its very own symbol g = -9.8 m/s 2 It is VERY important that you remember….THIS IS NOT GRAVITY!!!! g is an acceleration Gravity is a force g (little gee) is the symbol for the ACCELERATION CAUSED BY GRAVITY…NOT GRAVITY itself

g is a standard in a vacuum (the absence of matter), but most things fall in air. So why does a rock hit the ground before a feather? Air resistance! A feather interacts with the air more than the rock thus air slows down its acceleration considerably. Because of air resistance objects will not accelerate forever, they reach a maximum speed

Terminal velocity (or speed) is the maximum speed an object can reach when falling in air. As an object increases in speed, the effect of air resistance becomes greater. The force of air resistance & the force of gravity will eventually cancel each other out & the object will stop accelerating. Terminal velocity depends on air resistance. Air resistance depends on surface area, more surface area = lower terminal velocity The longer it accelerates, the faster it is going

How high was an object that was dropped from rest and fell for 12.6 s before hitting the ground? (Assume it fell in a vacuum)

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