CHAPTER 7Gravitation

UNIVERSAL GRAVITATION

What is Newton’s Law of Universal Gravitation and how do I apply it?

DEVELOPMENT OF THE MODEL OF THE UNIVERSE

Original model?

Copernicus – 1543

Brahe – 1560

No telescopes, measurements over 20 years

KEPLER

Brahe’s assistant

Applied geometry to the data

Sun is in the center

Orbits are ellipse shaped

Planets move faster closer to the sun

NEWTON

The apple falls, where does this force come from?

How does this apply to the motion of planets?

NEWTON

Third Law

Can be thought of as a force of attraction

Directly proportional to the masses of the objects

Can also be called gravitational force

Newton’s Law of Universal Gravitation

LAW OF UNIVERSAL GRAVITATION

• Measures the force of attraction between any two objects

• As small as electrons, as large as planets

RELATIONSHIPS BETWEEN THE VARIABLES

Between F and m

Between F and r?

What if we double m1?

What if we double r?

INVERSE SQUARE LAW

According to Newton’s equation, F is inversely related to the square of the distance.

SOLVING FOR VARIABLES

F can be Fg

If so, solve for g

Application?

Solve for mE

EXAMPLE

Find g if r = 1.5 m, density = 3.3 x 103 kg/m3

What would happen if the prince jumped upward?

HOMEWORK

Page 191 # 55 – 60, 64

G ?!

100 years after Newton

Cavendish – 1798

Confirmed that there is a gravitational attraction between two objects

Enabled the calculation of the mass of the Earth

MEASURING G

Original spheres were lead

Worked for any materials

HOMEWORK

Worksheet