# Balance and Plumb Lines: Two Experiments on Center of Gravity

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## What Is It?

Center of Gravity is the point on an object at which all weight is concentrated. As described by NASA’s Glenn Research Center, the center of

gravity is “the average location of the weight of the object.” The motion of a particular object is usually due to the shifting and changing of the center of gravity, or center of mass. For the most, determining the center of gravity of an object does not seem necessary. However, for any flying object, it is extremely important to know the center of gravity in relation to all other parts of the object in order to determine or predict how the object is going to move or react to certain situations.

## Center of Gravity Experiment #1 - Use Balance

During the first experiment to determine the center of gravity, you are asking where the center of gravity is located and using balance to find it.

Materials:

• Carrot
• Two forks
• Drinking glass
• Pencil

Procedure:

1. Insert the forks into the carrot on opposite sides to that the forks each stick out away from the carrot.
2. Balance the carrot on the edge of the drinking glass.
3. Describe how it is balancing and draw a picture of what you are seeing. Point out the center of gravity or where the weight needs to be centered in order to create balance.
4. Now, remove the forks from the carrot and position them so both stick out facing down, below the carrot.
5. Balance the carrot on the tip of the pencil.
6. Describe how it is balancing and draw a picture of what you are seeing. Point out the center of gravity or where the weight needs to be centered in order to create balance.

Conclusion: Explain what you learned when trying to find the center of gravity of an object.

## Center of Gravity Experiment #2 - Find Plumb Lines

In the second center of gravity experiment, you will find out how the principle learned could help a tightrope walker make it across.

Materials:

• Cardboard
• Strong weight (a washer or bolt works great)
• Hole punch
• Nail
• Pencil

Prodedure:

1. Cut the cardboard into a strange shape. Do not use a circle, square, rectangle, or any other common geometric shape.
2. Punch a hole near the edge of the cut-out cardboard piece and hang it from a nail.
3. Place the weight, a washer or bolt, on a thread and tie it off.
4. Hang the thread and weight from the nail in front of the cardboard.
5. Use a pencil to draw a plumb line down the cardboard where the thread touches. This marks your center line from that hanging point.
6. Repeat step 2 and 5 in two other places on the cardboard.
7. Remove the cardboard from the nail and balance on the tip of the pencil. You should know where to balance because it will be where all of the pencil plumb lines intersect, finding the center for you.

Conclusion: Describe how you found the center of gravity and how this concept could help a tightrope walker make it across to his destination.