Chapter 10- Gravity is more than Kepler's Laws Flashcards
Tidal Forces
Tend to stretch an object in the direction of the source of gravitational force. Gravitational forces decrease as you get further away from the source. If you place an object in Earth’s gravitational field, the near side of the object will feel a stronger gravitational pull than the far side. Cause of ocean tides.
Cause of Ocean Tides
Moon’s gravitational pull on Earth.
The gravity of the moon tugs harder on the oceans on the near side, an intermediate amount on the Earth itself, and less on the far side. This results in two tidal bulges. The ocean is pulled away from the Earth on the near side while the opposite happens on the far side.
High and low tides
Two high and low a day, 6 hours apart, as a point on Earth rotates through the tidal bulges in a 24 hour period. However, local conditions have a great deal of influence on the actual timing and height of the tides.
Why is the Moon more important than the Sun in causing tides?
Tides are caused by differential forces – the difference between the gravitational force on the near side of Earth and the gravitational force on the far side. This is greater for the gravitational forces of the moon than the sun. If Earth were placed in a uniform gravitational field, there would be no tides at all.
Spring Tides
When the Moon, Sun and Earth are all in line, the high tides are exceptionally high and the low tides exceptionally low.
Neap Tides
When the Earth-Moon line and the Sun-Moon line are at a right angle to each other, the tidal forces partially cancel each other out and the tides are rather mild.
Other effects of the tidal force
Friction between Earth and it’s oceans, slows down Earth’s orbit. Earth drags tidal bulge slightly ahead of a direct line from Moon to Earth. Moon pulls back on tidal bulge while Earth rotates forward.
Moon’s heavy side
Differentiation, heavier materials settled towards the center. Since Earth was pulling in one direction, the core settled slightly off center.
1:1 spin orbit resonance
Earth’s pull on the heavy side of the Moon causes it to always be pointed towards Earth, Moon rotates on its axis with the same period it orbits Earth.
Tidal flexing
Moon moves faster when closer to the Earth and slower when farther away. Interior of the moon is churned up a bit as heavier side is pulled towards Earth; but the constant rotation rate tries to pull it in a different direction.
Cassini Division
Gap in the rings of Saturn with few particles. If there were a particle, it would have a period of 11 hours. Period of Mimas is 22 hours. Every 22 hours they have the same positions; Mimas pulls particle out of orbit.
Roche Limit
Distance from a planet in which the differential and cohesive forces are the same; causing the planet to be torn apart.
Theory that the satellites of the gas planets were formed by a nebula; materials within the Roche Limit that couldn’t coalesce formed the rings.
Smaller satellites aren’t torn apart because they are held together by chemical bonds rather than gravity.
