1. Chapter 9 - Gravity
Tides
Black Holes

2. Ocean Tides
Tides are caused by the difference in gravity between the moon & earth on opposite sides of the earth (different distances)
The force is stronger wherever the moon is closer to the earth and weaker wherever the moon is farther, and water can move easily!
The high tide bulge follows the moon around the earth

3. Tides The sun also contributes to tides, but much less than the moon
The sun is less because the difference in distance from one side of earth to the other is not much when compared to the earth’s distance from the sun
The position of the sun, earth, and moon determines how high and how low tides are, along with the season of the year!

4. Tides
The highest high tides and lowest low tides happen when all 3 are in a line, or Spring Tides
Tide changes are smallest when they are not aligned, or Neap tides
Neap
Neap

5. Tides
High tides are even higher in winter because the earth’s center is closer to the sun in winter
The earth’s center is liquid, which results in “tides” in the earth’s crust
The atmosphere also has tides too! This is linked to “full moon” behaviors
The moon is slowing earth’s rotation

6. Earth’s Gravity—Below the Surface
What happens to gravity if you go down, inside the earth?
Gravity gets less and less the deeper you go because there is less mass.
Gravity at the center of the Earth is ZERO!
What would happen if there was a tunnel to the other side of the earth?
You would continuously oscillate back and forth from North to South Pole like game of ping pong!
Picture pg 166

7. Gravitational “Fields”
Force fields—gravity has a force field around any mass. It pulls other masses toward it and gets weaker with distance
Any force that acts at a distance, without contact, has a force field. Examples are magnetic and electric

8. Einstein and Black holes
Albert Einstein spent much of his life trying to explain what gravity is, and relate it to the other forces somehow
Visualized a gravitational field as a geometrical warping of four-dimensional space and time
“Don’t try. I can’t do it either.” -Einstein
His ideas explained Black Holes before they were found to exist
Pic pg 169

9. Black Holes
Black holes happen when a sun burns out and shrinks as it cools…
Inverse-Square Law – if the star shrinks to 1/10th it’s original radius, the force of gravity would increase by 100 and so on.
Stars mass does not change.
Escape velocity increases and eventually exceeds the speed of light – nothing can escape!

10. Universal Gravitation
Based on observing distant stars and galaxies, scientists confirm Universal Gravitation and use it to explain the Big Bang theory
Universe continues to expand.
Some scientists believe that eventually everything will stop moving apart and be pulled back together

11. Newton’s Influence
Newton’s laws changed science and civilization on earth
It can be tied to the industrial revolution
It can even be tied to the Declaration of Independence and Constitution through philosopher John Locke

12. Review Questions Distinguish between spring tides and neap tides.
If you could somehow tunnel inside a star, would your weight increase or decrease? If, instead, you somehow stood on the surface of a shrinking star, would your weight increase or decrease? Why are your answers different?