Newton’s Law of Universal Gravitation 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