Physics Lesson 11/19

Physics Lesson 11/19

Orbital Motion and Gravity

Open Ended

Thanksgiving Journal - Where did the first “Thanksgiving” on current US soil occur?

Practice Problems

You have 10 minutes, then we will move on.

Newton's Law of Universal Gravitation

• 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.

Newton's Law of Universal Gravitation

• 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's Law of Universal Gravitation

• 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?

Newton's Law of Universal Gravitation

• 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.

The Law of Universal Gravitation

• 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.

   $F_g=\frac{Gm_1m_2}{r^2}$  

Law of Universal Gravitation

• 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.

Open Ended

Exit Ticket - What is one way the force of gravity could be doubled?