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Balancing Act

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Balancing Act
Julee Murphy
ECDC/TAMUCC
Grade level: 3-5
Topics: Center of Gravity, Balance, Observing, Comparing and Contrasting, Applying
Literature connection: Mirette on the High Wire by Emily Arnold McCully
Objective: Students will investigate cause and effect and center of gravity (mass) of objects.
Materials:
Book-Mirette on the High Wire file folders or heavy weight cardstock
scissors
chart
paper
crayons /color pencils
templates of animals or clown
Gravity defying
bird model
Poster tack, pennies, paper clips or masking tape
3 pizza boxes1 empty pizza box
1 pizza box with a weighted object tightly secured in a far corner of the box
1pizza box with weighted object tightly secured mid way between the center of the box and a corner.
Procedure:
1. Display the amazing gravity defying (Magical) pizza boxes. Ask students how the boxes manage to
stay on the edge of the table without falling off. Prove to them they are not secured with any object.
Ask a student to reach out as you hand one of the boxes to them. The student will accept the box but
quickly struggle to readjust their grip as they realize the box is heavier on one side. Take a different
box and repeat the process. This box has a different center of gravity than the first box. Spend a short
amount of time examining the boxes without opening their lids. Ask student to offer explanations.
Have them write their explanations on the chart paper.
2. Display the gravity defying bird model. Ask students to infer why they think the bird can balance on
such a small balance point. Walk around students while balancing the bird on your fingertip. Students
will be amazed.
3. Pass out templates of frogs, birds, or clowns constructed from heavy weight card stock or file folders.
Color and cut out.
4. Students will attempt to balance their frogs, birds, or clowns on a balance point such as a fingertip or
pencil’s eraser top. Encourage discussion. Why do they have trouble balancing the object? How could
they improve the model to gain stability? Offer a choice of pennies, poster tack, paper clips and
masking tape. Let students decide how to add the weight to improve the object’s stability.
5. Next, students will next investigate, through trial and error, how to make their objects balance after
adding weight to the front legs of the frog, the hands of the clown or the feathers of a bird using tape,
or poster tack.
6. Hold a group discussion to explore student findings. Why did the added weight improve the object’s
ability to become stable?
The science behind the investigation:
All objects have a center of mass also known as the center of gravity. It is usually located near the center
of an object, but sometimes we can be visually deceived when the center of gravity is deliberately moved
to a far corner of an object in order to trick the observer as in the case of the magic boxes. Gravity is a
force that attracts one object towards another. The earth’s gravity pulls all objects down. An object does
not tip over easily if it is near its center of gravity. Any two or three-dimensional shape will balance on a
pivot point if the object’s center of gravity (mass) and its point are correctly aligned. If the center of the
object’s mass is below the balancing point, then the object becomes more stable. This explains why circus
tight ropewalkers use long poles that descend or dip below them as they cross a high wire (Mirette on the
High Wire connection). The point at which an object balances is called the balance point.
Balancing Act
PART II: Reaching a Balance
Materials: 12-inch plastic ruler and pennies
charts for each group
Procedure:
1. Students partner into twos.
2. Take a ruler and try to balance it on your finger. Find the place in “mm” where it is perfectly
balanced. This is the ruler’s center of gravity. Record the number on the chart.
3. Have a partner place a penny at the 1 cm mark. Move your finger so that the ruler balances with
the penny on it. Observe which direction and how far you have to move your finger so that the
ruler returns to a stable balanced state. Record on the chart the new location of your finger has
had to move to beneath the ruler.
4. Have your partner place a second penny on top of the first penny and move your finger to obtain
a stable and balanced state again. Record the new location.
5. Repeat the procedure up to as many pennies as you can.
6. Which direction is the balance point moving?
7. How does the distance move each time change?
8. Can you observe a pattern forming?
9. Share findings with the class.
Number of Pennies
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Balancing Point (mm)
TEMPLATES:
Balancing Bird template: http://www.education.com/worksheet/article/balancing-bird/
Frog template resource: http://www.raft.net
Clown resource-AIMS
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