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Universe 1
Astronomy 20 1
The Tidal ForceThe Cosmic stretching force.
Astronomy 202
Tides
Ocean Tides Usually two high tides, two low tides per day. Tidal range about 6 feet in California. High tides 1 hour later each day—Moon
connection.
Alma Inlet, Bay of Fundy
Astronomy 203
Tides
Bay of Fundy
Highest tides in world - over 50 feet!
Bay of Fundy
Universe 2
Astronomy 204
Tides
Orbital Motion Reprised
bigger R → smaller v
R
Astronomy 205
Tides
Space Station vcirc is greater at "bottom" of station; less at "top." Objects in the station drift to top and bottom. Tidal force = stretching force Force ∝ 1/r3
Astronomy 206
Tides
Space Station
You are orbiting the Earth in theSpace Station. Watching for a fewminutes, you notice that objects inthe Space Station:
1) drift toward the center of theSpace Station.2) drift toward the walls of the SpaceStation.3) just float around, not drifting in anyparticular direction.4) fall to the floor.
Universe 3
Astronomy 207
Tides
The Tidal Force
The Tidal Force is a stretching force.
Astronomy 208
Tides
The Tidal Force
It depends strongly on distance.
Astronomy 209
Tides
Tidal ForceApplications
1. Ocean tides2. Tidal braking3. Rings
Universe 4
Astronomy 2010
Tides
Ocean Tides
Two bulges Two high tides, two low tides a day.
Astronomy 2011
Tides
Sun Tides
The Sun also exerts a tidal force on the oceans.Given that the Sun is 400 times farther awaythan the Moon, one would predict that:
1. The Sun tides are greater than the Moon tides.2. The Sun tides and the Moon tides are about the
same.3. The Moon tides are greater than the Sun tides.
Astronomy 2012
Tides
Body Tides
Bulges are created in solids, too—body tides.
Earth Moon
Universe 5
Astronomy 2013
Tides
Tidal Braking
Early on, fast rotatingMoon.
Tidal force slows rotation. Result: synchronous
rotation.
Astronomy 2014
Tides
Tidal Braking
Tidal braking slows Earths rotation Day is 1 sec longer in 50,000 years.
Astronomy 2015
Tides
The Receding Moon
Moon getting 4 cm farther away every year. 4.5 Gyr ago, the Moon was only 1/10 as far—
Mile-high tides! Future: no more total solar eclipses. :(
Universe 6
Astronomy 2016
Tides
4 Billion Years Ago
Astronomy 2017
Tides
Check Question
The Moon will recede from theEarth…
1) Forever2) Until the Earth’s rotation period
equals a month3) Until the Earth stops rotating
relative to the stars
Astronomy 2018
Tides
Rings
Close to a planet, tidal force preventschunks from forming a moon.
Roche limit = 2.5 radii Inside Roche limit: rings Outside Roche limit: moons.
Dione, Tethys, & Saturn's rings