Gravity

Lab Assignment 9: Gravity
Instructor’s Overview
As you continue with your study of physics, you’ll learn that there are four
fundamental interactions in nature. These interactions are summarized in this
table:

Interaction

Comments

Relative strength

Effective range

Strong nuclear
force

Binds protons and neutrons in
nuclei

1

10-15 m

Electromagnetic
force

Force between charged
particles. Follows inverse-
square law.

10-2

Infinite

Weak force

Responsible for certain types
of radioactive decay

10-13

10-18 m

Gravitational
force

Force between all objects.
Determined by magnitude of
masses and separation.
Follows inverse-square law.

10-38

Infinite

So gravity is one of the four fundamental forces of nature. We will learn about
the other three in Physics II. Some interesting things to note about the
gravitational force:

In a relative sense, it is the weakest of the four fundamental interactions.
Even so, gravity is largely responsible for the dynamics of our solar system,
galaxy, and the Universe as a whole.

Gravity acts over an infinite distance. Objects may be separated by
thousands of light years, but they experience gravitational attraction.

Gravitational interactions obey the inverse-square law.

Coulomb’s Law dictating the force between two charged particles is also an
inverse-square relationship.
In this lab, you will perform experiments that illuminate the concept of
gravitational interaction.
This activity is based on Lab 10 of the eScience Lab kit.
Our lab consists of two main components. These components are described in
detail in the eScience manual. Here is a quick overview:

JWH
1 Physics I
Experiment 1: In the first part of the lab, you will subject a variety of
objects to the force of gravity and discuss your observations.
Experiment 2: In the second part of the lab, you will use a flashlight as an
analogy to demonstrate the inverse-square law of gravity.
Take detailed notes as you perform the experiment and fill out the sections
below. This document serves as your lab report. Please include detailed
descriptions of your experimental methods and observations.
Date:
Student:
Abstract
Introduction
Material and Methods
Results
Based on your results from the experiments, please answer the following
questions:
Experiment 1: Falling in a Gravitational Field
1. The following expression for the acceleration due to gravity works well for
objects near the Earth’s surface (G is the gravitational constant, Me is the
mass of the Earth, and Re is the radius of the Earth):
? = ???
?2
?
Use the above equation to calculate the gravitational acceleration at an
altitude of 100,000 meters above the Earth. By what percentage is this
acceleration different from that on the Earth’s surface?
2. How does air resistance alter the way we perceive falling objects?
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2 Physics I
3. Using the universal law of gravitation, show that the gravitational
acceleration experienced by an object is independent of its mass.
Experiment 2: Inverse Square Law
Data table

Distance from
wall

Diameter of light
circle

Radius of light
circle

Area of light
circle

NOTE: Be sure to specify your units.

How did the intensity (brightness) of the circle of light seem to changes as
you increased the source distance?

How did the area of the circle of light change as you moved farther away?
How does this relate to the gravity field of a body?

Make a plot of distance vs. area for the light shining from the cup to the wall
(plot the area data on the y-axis).

Draw a line of best fit through your data points, and comment on the general
shape of your plot. What kind of relationship does this indicate (i.e. linear,
exponential, logarithmic, etc.)?

If the amount of light shining from the flashlight is constant, the intensity of
light should decrease as the area it shines on gets larger. Using your plot
from question 2, sketch an approximate plot for light intensity vs. distance.

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6. If you moved too far away from the wall the circle of light probably became
very difficult to see. Is the intensity of the light circle ever zero? Is it correct to
say that gravity doesn’t exist between objects on opposite sides of the
galaxy?
Conclusions
References
JWH 4 Physics I
lab_9_assignment_pdf.pdf

Unformatted Attachment Preview

Lab Assignment 9: Gravity
Instructor’s Overview
As you continue with your study of physics, you’ll learn that there are four
fundamental interactions in nature. These interactions are summarized in this
table:
Interaction
Strong nuclear
force
Electromagnetic
force
Weak force
Gravitational
force
Comments
Binds protons and neutrons in
nuclei
Force between charged
particles. Follows inversesquare law.
Responsible for certain types
of radioactive decay
Force between all objects.
Determined by magnitude of
masses and separation.
Follows inverse-square law.
Relative strength
Effective range
1
10-15 m
10-2
Infinite
10-13
10-18 m
10-38
Infinite
So gravity is one of the four fundamental forces of nature. We will learn about
the other three in Physics II. Some interesting things to note about the
gravitational force:
In a relative sense, it is the weakest of the four fundamental interactions.
Even so, gravity is largely responsible for the dynamics of our solar system,
galaxy, and the Universe as a whole.
Gravity acts over an infinite distance. Objects may be separated by
thousands of light years, but they experience gravitational attraction.
Gravitational interactions obey the inverse-square law.
Coulomb’s Law dictating the force between two charged particles is also an
inverse-square relationship.
In this lab, you will perform experiments that illuminate the concept of
gravitational interaction.
This activity is based on Lab 10 of the eScience Lab kit.
Our lab consists of two main components. These components are described in
detail in the eScience manual. Here is a quick overview:
Experiment 1: In the first part of the lab, you will subject a variety of
objects to the force of gravity and discuss your observations.
Experiment 2: In the second part of the lab, you will use a flashlight as an
analogy to demonstrate the inverse-square law of gravity.
JWH
1
Physics I
Take detailed notes as you perform the experiment and fill out the sections
below. This document serves as your lab report. Please include detailed
descriptions of your experimental methods and observations.
Date:
Student:
Abstract
Introduction
Material and Methods
Results
Based on your results from the experiments, please answer the following
questions:
Experiment 1: Falling in a Gravitational Field
1. The following expression for the acceleration due to gravity works well for
objects near the Earth’s surface (G is the gravitational constant, Me is the
mass of the Earth, and Re is the radius of the Earth):
?=
???
??2
Use the above equation to calculate the gravitational acceleration at an
altitude of 100,000 meters above the Earth. By what percentage is this
acceleration different from that on the Earth’s surface?
2. How does air resistance alter the way we perceive falling objects?
JWH
2
Physics I
3. Using the universal law of gravitation, show that the gravitational
acceleration experienced by an object is independent of its mass.
Experiment 2: Inverse Square Law
Data table
Distance from
wall
Diameter of light
circle
Radius of light
circle
Area of light
circle
NOTE: Be sure to specify your units.
1. How did the intensity (brightness) of the circle of light seem to changes as
you increased the source distance?
2. How did the area of the circle of light change as you moved farther away?
How does this relate to the gravity field of a body?
3. Make a plot of distance vs. area for the light shining from the cup to the wall
(plot the area data on the y-axis).
4. Draw a line of best fit through your data points, and comment on the general
shape of your plot. What kind of relationship does this indicate (i.e. linear,
exponential, logarithmic, etc.)?
5. If the amount of light shining from the flashlight is constant, the intensity of
light should decrease as the area it shines on gets larger. Using your plot
from question 2, sketch an approximate plot for light intensity vs. distance.
JWH
3
Physics I
6. If you moved too far away from the wall the circle of light probably became
very difficult to see. Is the intensity of the light circle ever zero? Is it correct to
say that gravity doesn’t exist between objects on opposite sides of the
galaxy?
Conclusions
References
JWH
4
Physics I
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