Gravitational Interactions

Chapter 13

• The force of gravity between any two objects in space can be given with the equation:

FG = G

This means that the force of gravity is inversely proportional to the square of the distance between them which we call the

Inverse Square Law

m1m2

d2

What would happen if you fell through the earth?

• As you fall towards the center of the earth your velocity increases as you accelerate.

• Your acceleration diminishes as you get closer to the center. At the center of the earth, acceleration would be zero.

• Momentum would carry you to the far side of the earth at which point you stop and then start falling back towards the center.

What would happen if you fell through the earth?

Questions:

1. At what point(s) would your velocity be zero?

Answer: At the surface of the earth on each side of the hole.

2. At what point(s) would your acceleration be zero?

Answer: At the center of the earth

Weightlessness:

In space astronauts experience weightlessness. This is not because there is no gravity, but rather that orbiting astronauts are in free fall around the planet.

You can experience this effect for brief periods of time at amusement parks and jet planes.

In this diagram, you can see that the moon's gravitational force pulls on water in the oceans so that there are "bulges" in the ocean on both sides of the planet. The moon pulls water toward it, and this causes the bulge toward the moon. The bulge on the side of the Earth opposite the moon is caused by the moon "pulling the Earth away" from the water on that side.

http://science.howstuffworks.com

• Higher than normal HIGH TIDE

• Higher than normal LOW TIDE (A neap tide occurs when the difference between high tide and low tide is the least.)

Eclipses:

Solar Eclipses

Lunar Eclipses

• Stars that have burned all of the fuel that sustains their nuclear reactions can have several fates depending on their masses.

• A black hole results from the collapse of a massive star down to a very small diameter. Gravity is so strong within a black hole that no matter or energy (including light) is able to escape.

• Most if not all galaxies (including ours) are thought to have black holes at their centers.

– Black Holes forms from massive stars ( > 5-10 solar masses)

Black Holes

Star Falling into a Black Hole:

Quasars:

• Quasars result from supermassive black holes at the center of galaxies that emit jets of radiation as matter falls into them

• Quasars are the most luminous objects in the universe