Physics Lesson 11/19

In 1666, Isaac Newton began his studies of planetary motion.

Did an apple actually fall and hit him on the head?

Probably not.

He did wonder if the force that caused the apple to fall might extend to the Moon or even beyond.

Side Note - There is actually a Newton's Apple Tree at The University of York.

He found the following:

The magnitude of the Force (F_g) on a planet due to the Sun varies inversely with the square of the distance (r) between the centers of the planet and the Sun.

That is F_g is proportional to 1/r².

The F_g acts in the direction of the line connecting the centers of the two objects.

Newton found that both the apple's ane Moon's acceleration agree with the 1/r² relationship.

These force that Earth exerts on an apple and that an apple exerts on Earth are exactly the same, so

Why does the apple fall to the Earth?

Mass, that's why! Earth is much more massive than the apple.

The force between the objects is called the gravitational force.

Newton had another thought on this though.

He was confident that the same force of attraction would act between any two objects anywhere in the universe.

Thus the Law of Universal Gravitation

It states...

Objects attracts other objects with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between them.

F is directly proportional to m₁ and m₂. If the mass doubles, the Force of attraction doubles

The term G is the universal Gravitation constant and we will discull it when we return after Thanksgiving.

Another addition to the reference materials today.