• Skip to Page Content
  • Skip to Site Navigation
  • Skip to Search
  • Skip to Footer
American Museum of Natural History
Share
OLogy Home
Games
Reading
Hands-on
Videos
Biology
Biodiversity
Brain
Genetics
Marine BiOLogy
MicrobiOLogy
PaleontOLogy
ZoOLogy
Human Cultures
AnthropOLogy
ArchaeOLogy
Earth & Space
Astronomy
Climate Change
Earth
Physics
Water
Type keyword(s) to search OLogy

OLogy Cards > gravity

OLOGY CARD 066
Series: Astronomy

gravity

Gravity is the force of attraction between all objects in the Universe. Objects with more mass have greater gravitational pull than objects with less mass. Gravity keeps Earth and the planets orbiting around the Sun instead of floating off into space. What would the Universe be like without gravity?

Original theory: In 1687, Sir Isaac Newton published Principia Mathematica, which explained the theory of gravitational pull.
Characteristics: the force of attraction between all objects exists throughout the Universe.
Significance: one of four "fundamental forces" of the Universe; keeps our feet on the ground and the planets in orbit

What Goes Up...
As the story goes, Sir Isaac Newton (1642-1727) was sitting under an apple tree and admiring the Moon when an apple fell on his head. (Most historians agree that Newton did see an apple fall—but not that it actually bopped him.) At that moment Newton had an inspiration: the force pulling the apple down and the force keeping the Moon in its orbit around the Earth were one and the same. The force was gravity, and Newton explained that gravity pulls toward the center, not just down to the ground. In other words, the apple fell towards the center of the Earth, and his head just happened to get in the way.

Stars are shaped like spheres because:

gravity pulled them into that shape as they formed

they eroded into round shapes over millions of years

round shapes have less wind resistance

Correct!

Stars are round because gravity pulls their mass towards their centers. That's why you won't see any square or triangular stars.

An object's gravitational pull is affected by:

distance and mass

distance and brightness

mass and speed of light

Correct!

A more massive object has a stronger pull than a less massive one. This strength is also affected by distance—the closer the objects, the stronger the pull.

The Moon has no gravity.

Fact
OR
Fiction
?

Fiction

The Moon is less massive than the Earth, so its gravity pulls less than on Earth. Astronauts can jump high, but they don't float away.

Image credits: main image, © AMNH/Jim Paillot.

You might also like...

Sir Isaac Newton

Many historians consider English scientist Sir Isaac Newton the first modern physicist. He explained how gravity affects...

Meet the Universe's Main Attraction... Gravity

Find out why a ball thrown in the air will return to the ground. 

Space and Time

How do you describe your place in the 4th dimension?

Page footer
  • Contact Us
  • OLogy Cards
  • For Educators
  • Credits
  • Privacy Policy
  • Copyright
  • OLogy Sitemap