The Law of Universal Gravitation

The legend goes that Sir Isaac Newton developed his theory when an apple fell on his head

This made him think! Could the apple’s motion be related to how the moon moves?

He found that the moon “falls” around the Earth

If the Earth Wasn’t there, the moon would follow a straight line path due to ??????

So why is the moon “attracted” to the Earth? Is the Earth attracted to the moon?

Everything with a mass is attracted to everything else with a mass. The strength of the attraction depends upon the size of the masses and the distance between them.

INVERSE SQUARE LAW Because distance is on the bottom of the fraction, by whatever factor distance changes, Fgrav will change by that same factor, inversely squared

SOOOOOOOOO…. The more massive the objects are, the bigger the Fgrav The more distance between the masses, the SMALLER the Fgrav The less distance between the masses, the BIGGER the Fgrav

Try some problems! If the distance is X1/5, Fgrav will be X___________ If one Mass is X14, Fgrav will be X___________ If one mass is X3 and the other is X2 and the distance is X3, Fgrav will be X___________

How does Fgrav of the following planets compare? M 2M

What is the Fgrav acting between the Earth (m=5.98X10 24 kg) and a 70kg student if the student is at sea level, 6.37 x 10 6 m from the Earth’s center? Remember, G=6.67 X10 -11

Click on the link below to see the effect gravity has on projectiles