Download Ch 4 Feb 7

Newton’s third law of motion:
For every force, there is always an equal and opposite
reaction force.
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Clicker Question
How does the force the Earth exerts on you compare
with the force you exert on it?
A. Earth exerts a larger force on you.
B. You exert a larger force on Earth.
C. Earth and you exert equal and opposite forces on
each other.
© 2010 Pearson Education, Inc.
Clicker Question
How does the force the Earth exerts on you compare
with the force you exert on it?
A. Earth exerts a larger force on you.
B. You exert a larger force on Earth.
C. Earth and you exert equal and opposite
forces on each other.
© 2010 Pearson Education, Inc.
What keeps a planet rotating and
orbiting the Sun?
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Conservation of Angular
Momentum
Angular momentum = mass x velocity x radius
• The angular momentum of an object cannot change
unless an external twisting force (torque) is acting
on it.
• Earth experiences no twisting force as it orbits the
Sun, so its rotation and orbit will continue
indefinitely.
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Angular momentum conservation also explains why objects
rotate faster as they shrink in radius.
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Where do objects get their energy?
• Energy makes matter move.
• Energy is conserved, but it can:
– transfer from one object to another
– change in form
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Basic Types of Energy
• Kinetic (motion)
• Radiative (light)
• Potential (stored)
Energy can change type,
but cannot be created or
destroyed.
© 2010 Pearson Education, Inc.
Clicker Question
A rock held above the ground has ___.
A.
B.
C.
D.
Radiative energy
Kinetic energy.
Potential energy
Thermal energy
© 2010 Pearson Education, Inc.
Clicker Question
A rock held above the ground has ___.
A.
B.
C.
D.
Radiative energy
Kinetic energy.
Potential energy
Thermal energy
© 2010 Pearson Education, Inc.
Mass-Energy
Mass itself is a form of potential energy:
E =
• A small amount of mass can
release a great deal of energy.
• Concentrated energy can
spontaneously turn into particles
(for example, in particle
accelerators).
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2
mc
Conservation of Energy
• Energy can be neither created nor destroyed.
• It can change form or be exchanged between
objects.
• The total energy content of the universe was
determined in the Big Bang and remains the
same today.
© 2010 Pearson Education, Inc.
What determines the strength of gravity?
The universal law of gravitation:
1. Every mass attracts every other mass.
2. Attraction is directly proportional to the product of
their masses.
3. Attraction is inversely proportional to the square of
the distance between their centers.
© 2010 Pearson Education, Inc.
Clicker Question
If you double the distance between two objects, the
gravitational force between them __.
A.
B.
C.
D.
E.
doubles
quadruples.
is ½ the original force.
is ¼ the original force
Remains the same.
© 2010 Pearson Education, Inc.
Clicker Question
If you double the distance between two objects, the
gravitational force between them __.
A.
B.
C.
D.
E.
doubles
quadruples.
is ½ the original force.
is ¼ the original force
Remains the same.
© 2010 Pearson Education, Inc.
Clicker Question
If you double the mass of one of the objects, the
gravitational force between them __.
A.
B.
C.
D.
E.
doubles
quadruples.
is ½ the original force.
is ¼ the original force.
Remains the same.
© 2010 Pearson Education, Inc.
Clicker Question
If you double the mass of one of the objects, the
gravitational force between them __.
A.
B.
C.
D.
E.
doubles
quadruples.
is ½ the original force.
is ¼ the original force.
Remains the same.
© 2010 Pearson Education, Inc.
Clicker Question
Lastly, if you double the mass of both objects, and
double the distance between them, the gravitational
force between them __.
A.
B.
C.
D.
E.
doubles
quadruples.
is ½ the original force.
is ¼ the original force.
Remains the same.
© 2010 Pearson Education, Inc.
Clicker Question
Lastly, if you double the mass of both objects, and
double the distance between them, the gravitational
force between them __.
A.
B.
C.
D.
E.
doubles
quadruples.
is ½ the original force.
is ¼ the original force.
Remains the same.
© 2010 Pearson Education, Inc.