Unit 8: Universal Gravity

Key Points

Gravity acts at a distance
It attracts (never repels)
Gravity is a two action (N3L applies!)
It penetrates vacuum or other matter
Gravity seems to work for very large (Earth and Moon) and very small masses (Cavendish Experiment)
Not caused or affected by atmosphere, magnets, or spinning of the Earth. Only mass.
Unfortunately no simple intuitive model has been found to explain gravity. Einstein tried, String Theory attempts, but perhaps that is in your future to develop.
Gravity is proportional to the product of the masses and inversely proportional to the square of the radial distance (center to center) between the two masses
It is the same force of gravity that pulls an apple towards the Earth that pulls the Moon around the Earth (just diluted)
It is gravity that holds us on to the Earth, keeps the moon from moving off in a straight line away from the Earth, keeps the planets from moving in a straight line away from the Sun, keeps our Solar System from moving off in a straight line away from galaxy, and causes our galaxy to be attracted to other galaxies.
Understand how Newton's Three Laws can be applied to the Moon "falling" around the Earth
Understand how Cavendish found the gravitational constant "G" to complete the gravitational law
Understand how to use the gravitational law to determine how the force changes when a variable (like mass or distance) is doubled, halved, tripled, etc.
Understand how to use the gravitational law to solve for F, m1, m2, or r
Understand how to use the gravitational law to determine the acceleration due to gravity

Make sure you know how to do scientific notation on your scientific calculator!

Bill O'Reilly shows a complete lack of scientific literacy! From a physics standpoint this is NOT meant to be a discussion of religion but a discussion of science. Watch what Bill O'Reilly refers to at about 1 min 50 s for his "evidence" for religious beliefs and the response below by NDT.