Tides and Tidal Forces

Near Satellites Orbit Faster

What If Satellites Are Tethered?

The Tension Is Real

There are Two

Tidal Bulges

on Earth

Both Moon and Sun Cause Tides

Tides on the Real Earth

Tidal Friction

Tides Affect Earth and

Moon

Tides and the Earth-Moon System• Moon retreating at 4 cm/yr• Day currently lengthening by 2 sec/100,000 yr• Fossil organisms and some rocks preserve

tidal records• 600 million years ago– Day was 22 hours long– 400 days/year– Moon 13,000 km closer– Rate of change not constant

Tides and Planets• All satellites are locked to their parent planets• Large tides can heat planetary interiors• Tidal forces change orbital eccentricity• Most satellites– Planet rotation slows– Moon moves outward– Can “leak” away (Deimos)

• Retrograde Satellites– Satellite moves inward (Triton)