Download a M ~ g/3600

Fast Moving Projectiles: Satellites
The Earth satellite is simply a projectile that
falls around the Earth rather than into it.
A common misconception is that satellites
orbiting at high altitudes are free from
gravity.
The high altitude only allows the satellites to
go above atmosphere, but they are in the field
of the Earth gravity.
Question
A newspaper report reads in part, “ The space shuttle orbits Earth
at an altitude of nearly 200 miles and is traveling at a speed of
18,000 mph. The shuttle remains in orbit because the
gravitational force pulling it toward Earth is balanced by the
centrifugal force (the force of inertia) that is pulling it away from
Earth”. Explain why this newspaper should hire a new reporter.
Questions
A vine is just strong to support Tarzan when he is
hanging straight down. However, when he tries to
swing from tree to tree, the same vine breaks at the
bottom of the swing. How could it happen?
A common misconception is that satellites
orbiting at high altitudes are free from
gravity.
The high altitude only allows the satellites to
go above atmosphere, but they are in the field
of the Earth gravity.
Rotational Motion
Aristotle: There are two sets of
natural laws: one for earthly events,
and another, altogether different, for
motion in the heavens.
The Concept of Gravity
Newton’s Law of Universal
Gravitation
Whenever a body has a force exerted on it, that force is
exerted by some other body.
Every object on the surface of the Earth feels the force
and this force is directed toward the center of the Earth.
What about accepting this idea:
force, “acting at a distance” ?
What is the Centripetal
Acceleration of the Moon?
aM ~ g/3600
The Universal Law of Gravity
Force ~ mass1 x mass2/distance2
Question
1. The Moon falls around the Earth than straight into it.
If tangential velocity were zero, how would the
Moon move?
2. According to the equation for gravitational force,
what happens to the force between two bodies if the
mass of one of bodies is doubled? If both masses are
doubled?
Newton’s Law of Universal
Gravitation
Every particle in universe attracts every other particle with a
force that is proportional to the product of their masses and
inversely proportional to the square of the distance between
them. This force acts along the line joining the two particles.
F = G m1m2/r2
The Universal Gravitational
Constant G
F = Gm1m2/d2
G = 6.67 10-11 Nm2/kg
Gravity and Distance
The Inverse Square Law
The inverse square law holds for gravity and
for all phenomena wherein the effect from a
localized source spreads uniformly
throughout the surrounding space: the electric
field of an electron, light from a match….
Questions
1. If there is an attractive force between all objects, why do we
not feel gravitating toward massive buildings in out
vicinity?
2. Consider an apple at the top of the tree that is pulled by
Earth’s gravity with a force of 1 N. If the tree were twice as
tall, would the force of gravity be only ¼ as strong? Defend
your answer.
Weight and Weightlessness
To be more general we now refine the
definition of weight: weight of something is
the force it exerts against a support.
Question
In what sense is drifting in space far
away from all celestial bodies like
stepping off the table?
Ocean Tides
Question
We know that both the Moon and the Sun
produce our ocean tides, and we know that
the Moon plays the greater role because it is
closer. Does it closeness mean it pulls with
more gravitational force than the Sun on the
Earth oceans?