Question

1
Question

• The main reason ocean tides exist is that the
  pull of the moon
• A) and sun are in conjunction at high tides and
  in opposition at low
• tides.
• B) is greater on oceans closer to the moon and
  less on oceans
• farther from the moon.
• C) is greater on the Earth because the moon is
  closer to Earth.
• D) and the sun on the oceans are in opposite
  directions.
• E) none of these
• Answer

2

• Tides

3
Unit 3 Day 6 GRAVITY (chapter 9
pages 171-175)

• The earth is not a rigid solid but, for the most
  part, it is a molten liquid covered by a thin,
  solid, and pliable crust.
• As a result, the Moon Sun tidal forces produce
  Earth tides as well as ocean tides.
• Twice each day, the solid surface of the earth
  rises and falls as much as one-quarter meter!

4

• We live at the bottom of an ocean of air that
  also experiences tides, but we dont notice these
  tides (just like fish in deep water dont notice
  the ocean tides).
• Tidal effects in the upper part of the atmosphere
  (the ionosphere) produce electronic currents that
  alter the magnetic field that surrounds the
  Earth.
• These are magnetic tides.
• The highs and lows of magnetic tides are greatest
  when the atmosphere is having its spring tides
  (near the full and new Moon).
• This might explain why some people act
  differently during the time of a full moon.

5
Gravitational Fields

• The pattern of the Earths gravitational field
  can be represented by field lines.
• Any thing that comes into the vicinity of the
  Earth will be accelerated in the direction of the
  field line at that location.
• The strength of the Earths gravitational force
  follows the inverse-square law.
• It is strongest near the earths surface and
  weakens with increasing distance from the earth.

6
Gravitational Fields Inside a Planet

• Pretend that you could drill a hole from the
  North Pole to the South Pole.
• If you started at the North Pole end, youd fall
  and gain speed all the way down to the center and
  then lose speed all the way up to the South
  Pole.
• Without air drag the one way trip would take
  about 45 minutes.
• If you failed to grab the edge at the South Pole,
  you fall back toward the center and return to the
  North Pole in the same time.
• Your acceleration will decrease until it is zero
  at the Earths center.

7

• Imagine a spherical cavern at the center of a
  planet.
• The cavern would be gravity-free because of the
  cancellation of gravity forces in every
  direction.
• The size of the cavern doesnt change this fact
  even if it constitutes most of the volume of the
  planet!
• A hollow planet, like a huge basketball, would
  have no gravitational field anywhere inside it.
• A gravitational field would exist at and beyond
  its outer surface and would behave as if the all
  the mass of the planet were concentrated at its
  center but everywhere inside the hollow part,
  the gravitational field is zero.
• Anyone inside would be weightless.

8
Einsteins Theory of Gravitation

• In the early part of the twentieth century
  Einstein presented a model for gravity that was
  very different from Newtons.
• He proposed that a gravitational field was really
  a geometrical warping of four-dimensional space
  and time he said that bodies put dents in space
  and time somewhat like a massive ball placed in
  the middle of a waterbed dents the
  two-dimensional surface.
• The more massive the ball, the greater the dent
  or warp.
• http//10.70.0.82/SAFARI/montage/play.php?keyindex
  11213locationlocal

9

• If you roll a marble away from the ball, the
  marble will roll in a straight-line path.
• Roll the marble near the ball, it will curve as
  it rolls across the indented surface of the bed.
• If the curve closes on itself, the marble will
  orbit the ball in an oval or circular path.
• People who think like Newton will say that the
  marble curves because it is attracted to the
  ball they dont see the bed.
• Einstein said that the marble curves because it
  is following the curved surface of the waterbed!

10
Question

• If you drop a stone into a hole drilled all the
  way to the other side of the Earth (neglect the
  molten core), the stone will
• A) come to an abrupt stop at the center of the
  Earth.
• B) speed up until it gets to the center of the
  Earth.
• C) speed up until it reaches the other side of
  the Earth.
• D) slow down until it reaches the center.
• Answer

11
Question

• Half way to the center of a completely hollow
  planet with a thin uniform shell, your weight
  there compared to your weight on the outer
  surface would be
• A) one-quarter.
• B) one-half.
• C) three-quarters.
• D) the same as at the surface.
• E) zero.
• Answer

12
Question

• A supplier wants to make a profit by buying metal
  by weight at one altitude and selling it at the
  same price per pound at another altitude. The
  supplier should
• A) buy at a high altitude and sell at a low
  altitude.
• B) buy at a low altitude and sell at a high
  altitude.
• C) disregard altitude because it makes no
  difference.
• Answer

13
Einsteins Theory of Gravitation
14
Unit 3 day 7 Homework

• Page 180 review Questions 21 30
• Page 183 Exercises 46 52
• Page 183 Problems 2 3