Now Playing: Ch 13
Topic: Ch 13
CP Chap 13 Notes
13.1 Gravitational Fields
Gravitational Field
Can be represented by imaginary field lines
Where field lines are closer together, the gravitational field is stronger
Arrows show the direction of the field
Any object will be accelerated along the direction of the field line
Definition of gravitational field strength:
Gravitational Field Strength = Force per unit mass
Or
g = F/m
13.2 Gravitational Field Inside a Planet
g is less inside a planet:
the downward pull is lessened by the pull of the mass from above
at the center of mass of the planet, g would be zero
13.3 Weight and Weightlessness
13.4 Ocean Tides
Newton showed that ocean tides are caused by differences in the gravitational pull of the moon on opposite sides of the earth.
The moon’s attraction
Stronger on the earth’s oceans closer to the moon
Weaker on the earth’s oceans farther from the moon
Then why not one tide per day instead of two per day??
The earth’s waters get elongated as the earth rotates around the earth-moon CM
A bulge forms on both sides: the side closer to the moon and the side farther from the moon
Just as a ball of taffy will get elongated when spun in a circular path, earth’s waters elongate.
Why is there a “Dark Side of the Moon?”
The same side of the moon is always facing us
The moon is elongated because of gravitational pull to earth.
Because of torques, the moon settles into alignment with the earth’s gravitational field.
The sun’s contribution to ocean tides:
Not so much because the sun is so far away, so the difference between the near and far sides of the earth is negligible. The bulge is all about this difference.
“Full Moon,” “Spring” or “Flood” Tides—the Sun and moon are lined up together and their collective pull results in higher than normal high tides and lower than normal low tides.
Lunar Eclipse:
“Neap” Tides: We see a half moon
Tides due to pull of sun and moon cancel each other
Lower than average high tides, higher than average low tides
Electrical Power Production from Tides:: This one is in Brittany, France, built in 1968
The tilt of the earth causes the equal tidal bulges to be experienced as unequal.
13.5 Tides in the Earth and Atmosphere
Planetary Rings: tidal forces may have caused the formation of these rings
13.6 Black Holes
