# Physics Quest: Gravity

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

1. What is the equation for Universal Gravitation?
2. What is the value of the constant “G”?
http://www.physicsclassroom.com/class/circles/Lesson-3/Newton-s-Law-of-Universal-Gravitation
3. Describe the experiment that first accurately measured the constant “G”?
http://en.wikipedia.org/wiki/Cavendish_experiment
4. What does Einstein’s Theory of Relativity say causes gravity?
http://theory.uwinnipeg.ca/mod_tech/node60.html
5. 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.

1. What is true about the force of $m_2$ on $m_1$, and the force of $m_1$ on $m_2$? (two things)
2. 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.
3. 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.)
4. Keep the masses 4 m apart, but change one mass to 40 kg.  What is the new force of gravity?
5. 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”)
6. Change the 40 kg mass down to 10 kg.  What is the new force of gravity?
7. 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”)
8. Set both masses back to 20 kg, but move them so they are 8 m apart.  What is the new force of gravity?
9. 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”)
10. 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.