**Introduction:**

In this PhysicsQuest you will learn about Newton’s Law of Universal Gravitation.

**Instructions:**

- Answer all of the questions on a piece of paper using the links provided. If a link isn’t working, then find another website that can answer the question.
- All answers must be in your own words. Do not just copy and paste to your paper!

**Section 1: Background**

- What is the equation for Universal Gravitation?
- What is the value of the constant “G”?

http://www.physicsclassroom.com/class/circles/Lesson-3/Newton-s-Law-of-Universal-Gravitation - Describe the experiment that first accurately measured the constant “G”?

http://en.wikipedia.org/wiki/Cavendish_experiment - What does Einstein’s Theory of Relativity say causes gravity?

http://theory.uwinnipeg.ca/mod_tech/node60.html - What are some ways we think gravity is “transmitted”? In other words, how does it get from one object to another without any contact between the objects.

http://www.fnal.gov/pub/science/inquiring/questions/graviton.html

**Section 2: Application**

Answer the following questions using the Gravity Force Lab simulation from PhET at the University of Colorado. This should be able to run on computers, phones, and tablets.

- What is true about the force of on , and the force of on ? (two things)
- Using the equation for Universal Gravitation you found in Section 1, show the calculation for the force of gravity for the initial set up of the simulation.
- Set both masses equal to 20 kg, and set them both 4 m apart. You can move the masses and rulers. What is the force of gravity? (You will be comparing other answers to this answer.)
- Keep the masses 4 m apart, but change one mass to 40 kg. What is the new force of gravity?
- How did the force of gravity change (compared to #3)? (I’m looking for “doubled, tripled, halved, x2, x3, x ½, etc. NOT “got bigger”)
- Change the 40 kg mass down to 10 kg. What is the new force of gravity?
- How did the force of gravity change (compared to #3)? (I’m looking for “doubled, tripled, halved, x2, x3, x ½, etc. NOT “got bigger”)
- Set both masses back to 20 kg, but move them so they are 8 m apart. What is the new force of gravity?
- How did the force of gravity change (compared to #3)? (I’m looking for “doubled, tripled, halved, x2, x3, x ½, etc. NOT “got bigger”)
- Given the two masses of 20 kg 8 m apart, how can you change one mass to get back to the answer in #3? Try to predict your answer before trying it.