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Lesson Plan
INSTRUCTIONS FOR TEACHERS
Grade Level: 9-12
Curriculum Links: Earth and Space (SNC 1D: D2.1, D2.2, D2.3, D2.4)
Group Size: Groups of 2 - 4 students
Preparation time: 1 hour
Topics Covered
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•
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Gravity
Forces and Motion
Solar System
Description
The Gravity Well is a pliable surface used with balls of different masses to
demonstrate properties of orbiting bodies. Students can investigate forces and motion
in our solar system and beyond. Many students have the misconception that there is
no gravity in space. With the Gravity Well, students discover that the opposite is true:
the force of gravity is pervasive in space.
Students construct a Gravity Well and use it to investigate why the Sun is at the
centre of the Solar System and the influence of gravity on mass. By observing the
motion and interaction of the balls as they roll on the surface, students gain insight
into how the solar system is organized, the structure of galaxies and of the larger
universe.
Learning Objectives
By the end of this activity, students will be able to:
• Observe that gravity exists in space
• Demonstrate that a large mass has a stronger gravitational field than a small
mass
• Explain why the Sun is at the centre of the solar system
• Describe how Earth and other planets stay in orbit around the Sun
• Recognize the difference in mass, size and distance between the planets and
the Sun
• Define the word orbit and compare the orbits of different objects
• Recognize that planets closer to the Sun move faster than planets farther from
the Sun (e.g. Mercury orbits once every 88 Earth days, while Pluto orbits once
in 248.5 Earth years)
• Define the term “satellite” and discuss why Jupiter has many satellites
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Exploring Gravity Lesson Plan
Materials
For each Gravity Well:
• 1 large Hula Hoop (about 61 cm / 24 inches in diameter)
• Shrink film and double-sided tape from a window insulation kit, available at
hardware stores (Note: do not use plastic wrap)
• 8 medium Styrofoam cups
• 6 ball bearings of varying sizes and weights from 30 grams to 300 grams
(1 ounce to 10 ounces) or marbles with similar weights
•
at least one hair dryer and a few pairs of scissors available for the class
If you cannot find Hula Hoops:
Option 1
Use one-inch, semi-rigid polyvinyl tubing found in the plumbing section of a hardware
store. You can also use a garden hose. Connect both ends using a coupling. Ensure
the hoop is circular.
Math Activity
You may want to have your students do the following calculation to determine
the length of tube required to make a circle of 61 cm.
Diameter x π = Circumference
61 cm x
π = 192 cm
(π ≈ 3.14)
Option 2
Use a large, round container or bucket as an opening over which the film can be
stretched.
Gravity Well Procedures / Instructions
(See also Constructing the Gravity Well for a visual step-by-step depiction)
1. Place the Hula Hoop on the shrink film and cut the film to fit the Hula Hoop,
leaving about 8cm (3 inches) all around
2. Apply double-sided tape to the outside edge of Hula Hoop and press tape
firmly in place
3. Warm tape with the hair dryer, then peel the top layer from tape
4. Centre the Hula Hoop on the shrink film and press firmly in place
5. Use the hair dryer to “shrink” the film – start around outside edges and work
toward centre, keeping hair dryer at least 10cm (4 inches) away from film’s
surface. Important: Do not over-heat or film will break
6. Trim off excess film
7. Keep sharp objects away from the film to avoid puncture
8. The shrink film can be re-tightened at any time by re-heating
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Exploring Gravity Lesson Plan
Making a Base for the Gravity Well
9. Insert one medium Styrofoam cup into another cup so you have 4 sets of
double cups.
10. Place cups upside down on a flat even surface (table top is best). Cups should
be placed equidistant from each other
11. Place the bottom of the Hula Hoop on top of the Styrofoam cup base
12. Make sure the rim is facing upward so the balls do not roll off but stay inside
the Gravity Well
Background Information
Before using their Gravity Wells, have students discuss some key ideas, such as:
• What is a force?
• What is mass?
• What is gravity?
• What object is at the centre of our solar system? Why?
• What is an orbit?
Extensions
You may wish to have students explore the following (especially in grade 12):
• Stars can orbit each other in Binary Systems (e.g. Epsilon Lyrae, a binary star in
the constellation Lyra in which each star is also a binary system, the “DoubleDouble”)
• Astronomers measure the wobble of stars to detect extrasolar planets (planets
orbiting stars other than the Sun)
• Some objects that are massive but dense (i.e. packed into a small space), such
as neutron stars or black holes, can warp a region of space significantly,
resulting in a “gravitational well” from which objects are unable to escape
• Kepler’s second law of orbital motion states that planets closer to the Sun orbit
faster than those farther away
Newton’s Laws of Motion
1. An object at rest will remain at rest and an object in motion will remain in
motion unless a force acts on it
2. The force required to move an object is proportional to its mass
3. For every action there is an equal and opposite reaction
Resource Links
Discovering exosolar planets and interactive animation:
http://kepler.nasa.gov/Mission/QuickGuide
http://kepler.nasa.gov/multimedia/Interactives/
Newton’s Laws of Motion:
http://www.grc.nasa.gov/WWW/K-12/airplane/newton.html
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Exploring Gravity Lesson Plan
The Activity
Construct the Gravity Well(s). Divide your students into groups of 2-4 and distribute
Gravity Well materials and copies of Constructing the Gravity Well.
When your Gravity Wells are complete, distribute one copy to each student of the
Exploring Gravity Student Worksheet (Black Line Master).
Have students work in small groups to answer the questions on the sheet.
Answers to Student Worksheet
Our Solar System began to form about 4.6 billion years ago from a swirling
cloud of gas and dust. It is made up of the Sun, the planets, their moons,
asteroids and comets.
Gravity is a force that attracts objects to each other. All things exert some
gravitational force but the more mass an object has, the harder it “pulls”
objects around it. Stars have more mass than the planets, so a star’s
gravitational force keeps the planets in its solar system from drifting away.
You will use the Gravity Well to model the stars and planets and explore how
gravity plays a key role in the organization of our Solar System and beyond.
Make sure the Gravity Well is on a flat even surface (table top).
1. Roll one ball bearing in any direction. Describe what happens to the ball.
The ball rolled in a straight line from one end of the Gravity Well to the other.
2. Roll two or more small ball bearings (small mass) in a circle near the top of
the gravity well. Record your observations.
Both balls moved in a straight line with little interaction between the two.
3. Place one large ball bearing in the centre of the Gravity Well. Observe the
warping or curving of the vinyl. Replace the large ball bearing with a
medium ball and observe the difference of the warp in the Gravity Well. Try
a small ball bearing. Hypothesize what caused the greatest warp in the
vinyl and why?
The largest ball with the greatest mass created the deepest well or the largest
gravitational field.
4. First roll in a circle two or more small bearings and then roll a heavy (large
mass) ball bearing. Observe and describe what happens. Predict why?
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Exploring Gravity Lesson Plan
Small ball bearings moved in a straight line until the larger ball bearing was
released. The small ball bearings immediately moved around or “orbited” the
larger ball bearing.
Prediction: Smaller objects orbit more massive objects.
5. Place one heavy ball bearing in the centre of the Gravity Well. Roll one small ball
bearing in a circle near the top of the gravity well. Record your observations?
The small ball moved in an elliptical pattern around the larger ball, falling in a spiral
downward motion toward the centre of the Gravity Well. The gravity of the smaller ball
also had an influence on the larger ball causing it to wobble slightly,
6. Predict what causes the smaller ball bearing to spiral downward towards the
larger ball bearing at the centre.
The small ball eventually spiraled toward the large ball due to friction. The
Shrink Wrap and small ball bearing rubbed against each other, causing the
ball bearing to lose its kinetic energy.
7. Would this happen in space? (State your reason)
No because there is no friction in space. In space objects in motion tend to
stay in motion. The absence of friction prevents the Earth and the other
planets from spiraling toward the Sun or the centre of a solar system.
8. Roll two medium-weight balls with the same mass. Observe as they both
“orbit” around one another. Predict: Do stars perform in a similar manner?
Why / Why not?
Yes, two stars with similar masses and gravitational fields orbit each in what’s
called a Binary System.
9. Roll several ball bearings of varying masses at the same time. Record your
observations. Extrapolate how this explains the structure of our Solar
System.
The largest ball created the greatest warp in the vinyl which caused the
smaller objects to orbit around it.
The Sun has the largest mass and the strongest gravitational pull and
therefore, holds smaller objects like planets, asteroids and comets in orbit
around it.
10. Observe the speed of the smaller ball bearings as they approach the larger
ball bearing at the centre of the Gravity Well. Record your observation.
As the smaller ball approached the larger ball the orbit became smaller and
the velocity of the smaller ball increased.
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Exploring Gravity Lesson Plan
Assessment Plan
10 Points
- All observations are complete and recorded in the Student Worksheet
- Observations accurately describe the results
- Good use of adjectives to describe the observation
- Writing is clear and understandable
8 Points
- Most observations are complete and recorded in Student Worksheet
- Observations describe the results
6 Points
- Some observations are complete and recorded in Student Worksheet
- Observations attempt to describe the results
- Writing is difficult to understand
4 Points
- Few observations are complete and recorded in Student Worksheet
- Observations do not describe the results
0 Points
- No observations are complete.
- Observations are off topic or unrelated
- Writing is unreadable
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