Question

what did Galileo observe by placing two inclined planes facing each other and rolling down a ball from top end of one of them?

Answer 1

One of his greatest contributions  involved accurately measuring the effect of gravity on free falling bodies. Galileo hypothesized that a falling object would gain equal amounts of velocity in equal amounts of time, which meant that its speed increased at a constant rate as it fell. There was one problem, however, in testing this hypothesis: Galileo could not observe the object's free falling motion and at the time, technology was unable to record such high speeds. As a result, Galileo tried to decelerate its motion by replacing the falling object with a ball rolling down an inclined plane. Since free falling is essentially equivalent to a completely vertical ramp, he assumed that a ball rolling down a ramp would speed up in the exact same way as a falling ball would.

 

The Conclusion

Using a water clock, Galileo measured the time it took for the ball to roll a known distance down the inclined plane. After many trials, he observed that the amount of time it took for the ball to roll down the entire length of the ramp was equal to double the amount of time it took for the same ball to only roll a quarter of the distance. In other words, if you doubled the amount of time that the ball was rolling, it would travel four times as far.

Through this experiment, Galileo concluded that if an object is released from rest and gains speed at a steady rate (as it would in free-fall or when rolling down an inclined plane), then the total distance, s, traveled by the object is proportional to the time squared needed for that travel:

Answer 2

velocity is proportional to the two up and down inclined planes