An artist's rendering of some of the forces of the universe. The apple falling is of course from the story of Isaac Newton discovering the law of gravity as an apple fell from a tree he was sitting underneath.
Windows to the Universe original image
Gravity Definition Page
Gravity is one of the universal forces of nature
. It is an attractive force between all things. The gravitational force between two objects depends on their masses
, which is why we can really only see gravity in action when at least one of the objects is very large (like the Earth
Isaac Newton was the first scientist to define gravity using math. There will be a larger pull due to gravity if the objects' masses are larger and if the objects are closer together.
One thing we can do with Newton’s law is calculate an escape velocity for the Earth. That is the speed something has to go for it to escape the gravity of Earth. This number for Earth is about 11 km/s. This means that if you could throw a baseball at 11 km/s, it would never come down!
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