Transcript Gravitational Force

Gravitational Force
Newton’s Law of Universal
Gravitation
Gravitational Force
• Gravity is the weakest universal force
• Gravity pulls objects towards the center of the
Earth
• Gravity affects all objects in the universe
• It is the same force on a falling apple and the
force that keeps the moon in it’s orbit
Gravitational Force
• Gravitational force is an attractive force that
acts between any two masses
• Newton’s law of universal gravitation states
that every object in the universe attracts every
other object
Effects of Gravitational Force
• In the example of the falling apple, the Earth
exerts a force on the apple and the apple
exerts an equal force on the Earth
• You also exert a force on your textbook and
your textbook exerts a force back on you
• Your mass and the mass of the textbook is so
small that you do not notice the force of
gravity pulling your textbook towards you
Mass Matters
• There needs to be a large mass like the Earth
for a large gravitational force
• A larger mass has a larger gravitational force
• Gravitational force is also affected by the
distance between the two objects
Gravity and Distance
• The gravitational force between two objects is
proportional to their masses
• Gravitational force decreases as the distance
between masses increases, it will decrease
with the inverse square of the distance
between objects
• For example if the distance between two
objects doubles (x2) then the gravity will be ¼
(1/22) as strong
Gravity
• Gravity is the weakest universal force, but very
effective over long distances
• Gravity keeps us on the Earth, keeps the
moon, planets and stars in orbit
• The sun’s mass is about 300,000 times the
mass of the Earth so the sun’s gravitational
force is much stronger than the Earth’s
Earth, Moon and Tides
• Earth’s gravitational force keeps the moon in a
nearly circular orbit around the Earth
• The earth’s gravitational force is a centripetal
force that keeps the moon in its path
• The gravitational pull of the moon causes two
bulges in Earth’s oceans
• The moon causes two high and two low tides
per day