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Getting to Know Newton: Finding the Center of Gravity

The Task

Students explore the center of gravity of common objects such as a meterstick and a pencil. They are challenged to design and cut out an unusual shape and find its center of gravity. Students use their bodies to further investigate balancing points.

Materials

Clown balancing another clown on one hand
(per student group) (per student pair)

Leading the Activity

Clown balancing ball on one finger

Explain that objects are balanced when the weight of the object is evenly distributed around a point. This balancing point is the center of gravity of the object. Challenge students to think about and discuss how a pencil would be placed (horizontally) on the index finger to achieve balance. Encourage them to try balancing the pencil and share the results. Explain that the point at which the pencil is balanced is the center of gravity. Encourage student groups to explore Part 1 and Part 2 of the activity. Involve them in a discussion which compares the balancing meterstick with a first class lever.

After completing Part 2 of the investigation, invite students to stand with their feet together and their arms down by their sides. Ask them to think about and discuss what it means for our bodies to be balanced. Challenge students to stand on one foot and describe what happens. Encourage them to find a way to balance, while standing on one foot, without touching other objects. Discuss the ways that they balance themselves and have seen other people shift their center of gravity in order to achieve balance.

Procedure

Part 1: Student Groups:
  1. Predict and record where the meterstick will balance on a hand.
  2. Balance the meterstick on a hand.
  3. Record the results; discuss and record your conclusions.
  4. Put a ball of clay on the meterstick 15 cm from the end.
  5. Predict and record where the meterstick will balance on a hand.
  6. Balance the meterstick on a hand.
  7. Record the results; discuss and record your conclusions.
  8. Repeat Steps 4-7 two more times placing the clay ball at a different location on the meterstick each time.
  9. Record the results; discuss and record your conclusions.
Part 2: Student Pairs:
  1. Design and cut an unusual shape from the posterboard square. (Use as much of the posterboard as possible for the shape.)
  2. Mark an "X" on the shape where you think the center of gravity is located.
  3. Tie one end of the string to the washer and make a loop with the other end.
  4. Loosely attach the shape to a bulletin board with the push pin.
  5. Place the loop of the string over the push pin with the washer hanging straight down.
  6. Draw a straight line on the posterboard along the string.
  7. Repeat Steps 4-6 for each side of the shape.
  8. Make a dot at the point where all the lines cross.
  9. Place the shape on the top of the pencil eraser at the dot and try to balance it.
  10. Draw a picture of your unusual shape on the back of the activity sheet and label the center of gravity.
  11. Record your observations and conclusions under the drawing.

Range of Results

Clown balancing self on one hand

Students may initially find it challenging to balance the pencil on their index fingers. Encourage them to keep trying until they experience success. Remind students to think about how the pencil might be placed, and then to slowly and carefully place it on the finger. When working with the meterstick, first explain and demonstrate to the students how to position their hands with the thumb up and the hand perpendicular to the floor. Allow time for each student in the group to balance the meterstick (without the clay ball) on the hand. Encourage students to be aware of safety precautions while participating in the activities.

Teacher Background Information

Every object has a center of gravity. The center of gravity is the point around which the weight of the object is evenly distributed and it can be balanced. As students use the string and washer "plumb line," they search for the center of gravity of the unusual shape. The point at which the lines drawn from each side of the shape intersect is the balance point which represents the center of gravity. Our bodies also have a center of gravity which is near the waist. As you carry a heavy object in front of your body, you tend to lean backwards to keep your "balance"; or if you carry a heavy object on the left side of your body, you tend to lean to the right. Our center of gravity shifts to help us keep our balance.

 

 

 

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