What do a falling apple and an orbiting moon have in common?

if you fall an object will fall. It’s a move we’ve all seen hundreds of times. We’ve also seen a lot of the moon, which makes a complete orbit around our planet. every 27.3 days (as seen from Earth). Falling and orbiting may seem like radically different types of movement, but they’re not! The same physics explains them both.

There is a famous story about Isaac Newton making the connection thanks to a falling apple. (Probably not true—but could be.) Still, its making is an amazing thing, so I’ll walk you through the whole process. It includes some concepts that people living today may take for granted, but the construction of knowledge like this is not trivial, and Newton did not figure it all out on his own. It was based on ideas from Galileo, who studied the motion of falling objects, from Robert Hooke, who explored the effects of things moving in circles, and from Johannes Kepler, who produced ideas about the motions of the planets and the moon.

falling objects

Let’s start with what happens to an object when it falls. In the third century B.C. C., Aristotle stated that a massive object will fall faster than one of little mass. Sounds reasonable, right? That seems to fit what we see: he imagines dropping a stone and a feather at the same time. But Aristotle did not like to test his theories with experiments. it just seemed make sense that a heavier object falls faster. Like most of his fellow philosophers, he preferred to draw conclusions based on parlor logic.

Aristotle also reasoned that objects fall at a constant velocity, which means that they do not slow down or speed up as they go. He probably came to this conclusion because falling objects fall quickly and it is very difficult to detect changes in velocity with the naked eye.

But much later, Galileo Galilei (who went by his first name because thought that was cool) came up with a way to slow things down. His solution was to roll a ball down a ramp instead of dropping it. Rolling the ball at a very small angle makes it much easier to tell what’s going on. It might look something like this:

Video: Rhett Allin

Now we can see that as the ball rolls down the track, its speed increases. Galileo suggested that during the first second of movement, the speed of the ball will increase by a certain amount. It will also increase by the same amount of speed for the next second of movement. That means that during the time interval between 1 and 2 seconds, the ball will travel a greater distance than it did in the first second.

He then suggested that the same thing happens as the steepness of the angle increases, since it would produce a greater increase in speed. That must mean that an object on a fully vertical ramp (which would be the same as a falling object) would also increase in speed. Boom, Aristotle was wrong! falling objects No They fall at a constant speed, but rather change speed. The rate at which velocity changes is called acceleration. On Earth’s surface, a dropped object will accelerate downward at 9.8 meters per second per second.

We can mathematically write acceleration as a change in velocity divided by the change in time (where the Greek symbol Δ indicates change).


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