gravity is 9.81m/s but how was Galileo able to determine that number ?
think he didnt
He did his experiment in an airless place. Therefore; by the help of basic physics rules, he can solve the problem with just the time that is same for all matter in an airless place during freely fall.
I hope u understand.
Air or no air, you can measure g reasonably accurately just by timing the period of a pendulum.
He rolled balls down a ramp, he marked the location of the ball with each tick of a metronome. With these measurements he deduced the fact that an object falling fell at a constant rate (of increase) independent of the mass.
He certainly did not express the constant in terms of meter/sec^2, since the meter was not introduced as a unit of distance for another 200yrs after his death.
Galileo never quite got the accuracy of 9.8. Here is a summary from another website:
The first systematic tests of the universality of free fall were done by Galileo , who measured the acceleration of freely falling objects, or of objects rolling down an inclined plane. Such an approach suffers from great inaccuracies, which are related to the short time scales involved. Indeed, Galileo was unable to accurately determine g, the gravitational acceleration at the surface of the Earth, due to the lack of an accurate clock. Galileo concluded that a much better way to check the universality of free fall was to use a pendulum. Newton, and following him others, improved on Galileo’s experiments, and were able to determineg quite accurately.
and he was imprisioned by the church for his thoughts about gravity
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