Lab 11: Newton's Laws, Planetary Orbits
Introduction
Don't Panic

words inscribed in large friendly letters on the cover of the Hitchhikers
Guide to the Galaxy
by Douglas Adams
. The introduction to this lab includes a number of
equations and the exercise requires a calculator. Do not let the equations frighten you 
they are the language of this part of the Universe. If you follow the instructions, the units
will take care of themselves: work through the worked example on your own calculator to
ensure that you are using your calculator correctly
.
Newton's Laws
Up to the midseventeenth century, Planetary motions were predicted through equations
that were based solely upon observations (Kepler's laws), with no theoretical basis for the
equations. Isaac Newton made three
assumptions
, now called
Newton's Laws of
Motion,
about the interactions among force, mass and motion, and showed that the
equations used to describe planetary motions followed directly from these assumptions.
Newton's First Law
or the
Law of Inertia
. A body remains at rest, or moves In a
straight line at constant speed, unless acted upon by an outside force. This law introduces
the concept of acceleration, which is defined as a change of speed and/or a change in
direction. Without an external force, a body will not accelerate. Acceleration
is defined as
the rate at which the speed of a body changes in a particular direction. As a car
accelerates from a stop light, its speed changes in the forward direction. As a car turns a
corner, it accelerates sideways! It moves in a direction perpendicular to its original
motion, in addition to moving in its original direction, resulting in a curved path.
Newton's Second Law
. The acceleration of a body is proportional to the external force
acting on the body and the mass of the body. This law is commonly expressed as an
equation which states that if a force
F
acts on a body of mass
m
, it will accelerate In the
direction of the force at rate
a
given by:
Equation 1.
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View Full DocumentThe mass of a body is a measure of the total amount of material in the body, and is
usually measured in grams or kilograms. Mass should not be confused with weight,
which is a force caused by the Earth's gravity, and is given by the product of the mass and
the acceleration caused by Earth's gravity (about 9.8 meters per second per second, or 9.8
m/s
2
).
Newton's Third Law
. Whenever one body exerts a force on a second body, the second
body exerts an equal and opposite force on the first body. This is the famous statement of
action and reaction: every force has an equal and opposite reaction. As your weight
pushes down upon the floor, the floor pushes back with an equal but opposite force,
canceling the force of your weight.
In addition to the three laws of motion, Newton also formulated a general statement
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 Spring '09
 C.V.
 The Hitchhiker's Guide to the Galaxy, Sir Isaac Newton, Kepler's laws of planetary motion, Celestial mechanics

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