Gravity Lab Introduction
Name
Date_____________________________ Block ______________
Introduction: In this lab, computer simulation, we will investigate
the factors that effect gravitational force. We know that in order to
feel or see the effects of gravity a very large mass is required.
1. Go to http://phet.colorado.edu/en/simulation/gravity-force-lab
2. Select RUN NOW. (You may have to download it. You might
also try and see if it will run in HTML 5. Your instructor might
tell you which is better.)
Note: The force will be a very small number. To make taking the data
easier we will only look at the last six digits. In the example to the right
we would record the force as 003,963 nanoNewtons or 3,963 nN.
Qualitative Observations: (circle correct answer for 1-6)
Prediction: In this part of the lab you will be moving the masses closer
together and farther apart. You will also be increasing and decreasing the masses while keeping the distance
constant. Make a prediction as to what you think will happen as your change the distance:
Distance predication:
Mass prediction:
(circle correct answer for 1-6)
1. Move the masses closer. When they move closer the force between them becomes (Greater/Less/the
same)
2. Move the masses further apart. When the masses move away the force between them becomes
(Greater/Less/the same)
3. Double Mass 1. When mass 1 is doubled the force between them becomes (Greater/Less/the same)
4. Cut Mass 2 in half. When the mass is reduced the force between them becomes (Greater/Less/the same)
5. In any of the situations did the forces on the two masses ever differ in magnitude? (Yes / No)
6. In any of the situations did the forces on the two masses ever not point in opposing directions? (Yes / No)
7. What physics LAW explains questions 5 and 6 (either give name or definition)
Written by: Steve Banasia [email protected] Modified by MBH 11-16-13
Quantitative Data Collection:
Part I: MASS—It is now time to build a model. First, let us examine the relationship between masses.
 Separate Mass 1 and Mass 2 so that their centers of mass (black dots) are 6 meters apart.
 Set Mass 2 to 30.0 kg.
 Start Mass 1 at 0 kg. Increasing the mass each time with 1 kg and collect the data for gravitational force
until you have 10 data points.
Mass 1
Mass 2
Distance
(m)
Force
(nN)
Mass 1
0 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
Mass 2
Distance
(m)
Force
(nN)
1. Sketch a graph. Note: Gravitational force is the dependent variable (Y axis) and Mass 1 being
independent (X axis). (A blank graph is at the end of this packet.)
2. Redo the experiment but set Mass 1 to 30.0 kg and vary Mass 2. You will collect data on Mass 2’s
relationship to force.
Analysis: (USE COMPLETE SENTENCES AND REPHRASE THE QUESTIONS)
1. Does it matter which mass increases?
2. What type of relationship is there between Mass and force? (Use the following sentence: “As mass
increases, gravity ….”)
3. Are mass and gravitational force proportional or inversely proportional to each other?
Written by: Steve Banasia [email protected] Modified by MBH 11-16-13
Part II: DISTANCE—Let us examine the relationship between masses.
 Set both masses to 30.0 kg.
 Collect 10 data points of different distances between the masses. Note you can move the ruler and the
masses to maximize your range.
Mass 1
Mass 2
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
30 kg
Distance
(m)
Force
(nN)
1. Sketch a graph of Force vs. Distance (F vs. d)
Analysis:
1. What is the relationship between distance and the force of gravity? (Use the following sentence: “As
distance increases, gravity ….”)
Written by: Steve Banasia [email protected] Modified by MBH 11-16-13
Optional Challenge:
-Sketch a graph of Force vs. 1/ Distance (F vs. 1/d)
-Sketch a graph of Force vs. 1/ Distance squared (F vs. 1/d2)
1. What is the actual relationship between distance and the force of gravity?
2. See if you can write out the proportions between Mass 1 (m1), Mass 2 (m2) distance (r) to the Force of
gravity (Fg).
Fg
Check with your instructor to make sure your proportionality (combination of (m1), (m2) and (r)) is correct. If
you are correct, you should notice entering lab data for m1, m2, and r does not equal Fg. Also work out your
units, do they equal a Newton? This means there is also a constant (G) that we need to multiply to our
proportionality to complete our formula.
3. Make a graph of Force vs. your proportionality; this will help determine your constant (G)
4. Determine the gravitational constant (G) that will multiply to your units. Give k its proper unit too.
Hint, all your units combined need to = a Newton.
G=
5. Write your full formula and check with your instructor. Congratulations!
Written by: Steve Banasia [email protected] Modified by MBH 11-16-13
Force vs Mass 1
Force (nanoNewtons)
Force vs Distance
Force (nanoNewtons)
Written by: Steve Banasia [email protected] Modified by MBH 11-16-13