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REGENTS PHYSICS
STUDENT NOTES-MECHANICS
UNIVERSAL LAW OF GRAVITATION
GRAVITY - is the way that masses _______________________ with each other.
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Every mass in the ___________________ reaches out to attract every other mass.
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Every mass feels an ______________________ from every other mass.
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Gravity is a force of _________________________ between masses.
SIR ISSAC NEWTON - was puzzled by an apple falling from a tree.
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Postulated that ____________________ pulled the apple to the Earth. Thus the
apple “fell” to Earth.
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He extended this idea to the moon. He observed that the moon revolved around
the Earth.
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The moon ___________ to Earth but never crashed into the earth due to its high
_______________________ velocity.
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Newton could not finish his theory mathematically so he put his papers in a
drawer until he had developed __________________. This took him 20 years!!
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The moon is not the only body to “fall” around the Earth. Man made satellites
also fall around the Earth.
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The Earth, in turn, is a smaller mass than the _____________. So the Earth “falls”
around the Sun.
NEWTON’S UNIVERSAL LAW OF GRAVITATION
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Newton discovered that there were two things that dictated how much
“gravitational pull” a an object could have on another object.
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That is MASS and ___________________________.
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He developed from this the Universal Law of Gravitation.
F = Gm1m2
d2
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Double one of the masses, _____________________ the gravitational force of
attraction.
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Double the distance between the masses, reduce the force of attraction by
_____________________.
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This is known as the __________________ square law.
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G is called the Gravitational Constant. It is very small. Look on your reference
tables and write it down here… ____________________________________
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In other words, two masses of 1 kg each at a distance of 1 meter would have a
gravitational pull to each other of only _____________________________!!!
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The force of gravity is an extremely ________________ force.
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We only sense this force when there is a very large force (like the Earth).
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As you move away from the earth, the force of attraction of you to the Earth will
decrease by the inverse square law.
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But it will never be zero. Even at the other end of the ___________________.
The Earth would reach out and “touch” you.
SAMPLE PROBLEM: Determine the gravitational force of attraction between the
Earth and the Moon. Use your Reference Tables.
GRAVITATIONAL FIELD STRENGTH - a region in space where a small mass
would experience a gravitational field.
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Every mass is _________________________ by a gravitational field.
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The force vectors always point ___________________ the earth.
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The vector lines represent the gravitational _________________.
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An object would travel along these lines as it accelerated towards the Earth.
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The field strength is greatest nearest the Earth. Where the force vectors are
_____________________ together.
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The gravitational field strength can be determined mathematically using…
g=
Fg
m
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Another name for the gravitational field strength is the acceleration of the
object. It is 9.8 m/s2 at sea level.
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The acceleration is in the same _____________________ as the gravitational
force.
WEIGHT - is a combination of your mass and your proximity to a LARGE mass like
the Earth.
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Weight = Force
F = ma
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In the above equation, F is your weight.
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As you travel away from Earth, your acceleration to the Earth would
_______________. This would reduce your weight.
ELEVATOR QUESTIONS
You have a mass of 60 kg at sea level.
(1) What is your weight in an elevator that is stationary?
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(2) What is your weight if the elevator begins to accelerate upwards? More, less or
the same?
(3) What is your weight if the elevator travels upwards at a constant speed? More,
less or the same?
(4) What if the elevator accelerates downwards? More, less or the same?