1. Free Fall

2. Discussion Do objects fall at the same speed?
Do falling objects accelerate at the same rate?
How does air resistance affect a falling object?

3. Galileo (1564 – 1642)
“And yet it moves!”

4. Aristotle and Galileo
A rock will fall back to the earth to be with the other rocks. Since a big rock possesses more "earth", it will fall faster than would, say, a feather.
Galileo did not, as is popularly believed, state that the objects would hit the ground at the same time – he understood air resistance. He did understand that without air resistance, the objects would fall at exactly the same rate.

5. Free Fall Demo

6. Free Fall Demo
Although Galileo could not produce a vacuum, he could imagine, a chamber without the interference of air resistance. Galileo realized that inside that chamber all bodies would fall not at the same speed but at the same constant rate of acceleration. To describe this motion Galileo introduced the idea of average acceleration as the change in velocity over the time interval.

7. What does it all mean? Occurs when an object falls unimpeded.
Gravity accelerates the object toward the earth.