The Law of Universal

Gravitation

Newton’s Law of Universal Gravitation

Newton Did not discover gravity, but he did discover gravity was universal. In other words, everything pulls on everything else.

States:Every object attracts every other object with a force that for any two objects is directly proportional to the mass of each object, and indirectly proportional to the distance between them.

In Simple Terms:The greater the mass, the greater the attraction. The greater the distance, the weaker the attraction.

Universal Gravitational Constant

There is a constant in value for this universal attraction

Symbol:G

Value:6.67 X 10-11 Nm2/Kg2

Formula:

F= G(m1m2/d2)

Where “d” is the distance between the center of mass for the two objects.

What is “G”?• “G”, or the Universal Gravitational

Constant – first measured by Henry Cavendish 150 years

after Newton’s discovery of Universal Gravitation

• Shows us that the force of gravity is a very weak force

• Easy to notice with large masses, difficult to notice with small masses

Sample QuestionThe gravitational force of attraction between

Earth and the sun is 1.6 x 1023 N. a) What would this force have been if Earth

were twice as massive?b) What would the force be if the distance

doubled?

Sample QuestionOliver, whose mass is 65 Kg, and Olivia, whose

mass is 45 Kg, sit 2.0 m apart in their physics classroom. A) What is the force of gravitational attraction between Oliver and Olivia? B) Why don’t they drift towards each other?