4.15 Newton’s Law of Gravity
4.15 Newton’s Law of Gravity
- Describe Newton’s law of universal gravitation, and explain why it was so important.
- Identify factors that affect the strength of gravity between two objects.
You may have heard a story about Isaac Newton coming up with the idea of gravity when an apple fell out of a tree
and hit him in the head. The story isn’t true, but seeing how things like apples fall to Earth helped Newton form his
ideas about gravity, the force of attraction between things that have mass. Of course, people had known about the
effects of gravity for thousands of years before Newton came along. After all, they constantly experienced gravity
in their daily lives. They observed over and over again that things always fall toward the ground. However, it wasn’t
until Newton developed his law of gravity in the late 1600s that people knew gravity applies to everything in the
universe that has mass.
Newton’s Law of Universal Gravitation
Newton was the first one to suggest that gravity is universal and affects all objects in the universe. That’s why
Newton’s law of gravity is called thelaw of universal gravitation. Universal gravitation means that the force that
causes an apple to fall from a tree to the ground is the same force that causes the moon to keep moving around
Earth. Universal gravitation also means that while Earth exerts a pull on you, you exert a pull on Earth. In fact, there
is gravity between you and every mass around you—your desk, your book, your pen. Even tiny molecules of gas
are attracted to one another by the force of gravity. You can learn more about Newton’s law of gravity and how he
developed it in the video at this URL:
http://www.guardian.co.uk/science/interactive/2012/mar/12/newton-law-gravity-audio-slideshow
Q: Newton’s law of universal gravitation had a huge impact on how people thought about the universe. Why do you
think it was so important?
A: Newton’s law was the first scientific law that applied to the entire universe. It explains the motion of objects not
only on Earth but in outer space as well.