Galileo's Ingenious Marble Acceleration Track

Galileo's investigation of balls rolling down a variety of tracks led him to develop the idea of accelerated motion. He used an inclined plane to slow down falling motion, discovering that the distance an object travels is proportional to the square of the time it falls. By rolling the same size ball of different masses down the incline, he observed that each ball accelerated at the same rate, proving that, in the absence of air resistance, all objects fall at the same speed. Galileo correctly inferred that in a vacuum, all objects, regardless of mass, fall with the same constant acceleration (what we now call gravitational acceleration, approximately 9.8 m/s²).

Personal note: Yes I am back in the classroom again as a long-term substitute after being retired and occasionally substituting. This makes my 48 year in the classroom. I've now had two students tell me I taught the grandfathers.

track videos:

high low track race: https://www.youtube.com/watch?v=_GJujClGYJQ
building marble track: part 2 https://www.youtube.com/watch?v=iHvBoij7-7k
marble track review: https://www.youtube.com/watch?v=JWtsOiVxIIE
big high low track: https://www.youtube.com/watch?v=88NZStgiIt0
high road low road race track: https://www.youtube.com/watch?v=DCMQRPQS9T4