One of the most fun things to do as a kid is to spin around really fast and get dizzy. Our sense of balance comes from our ears and the liquid inside them that sometimes gets sloshed around. When it calms down, the dizziness generally goes away.

Balance is a difficult condition to understand. So is the question of why some people get dizzy riding in the back seat of a car or on a boat while others can ride the wildest roller coasters or perform as gymnasts or figure skaters and never get the slightest bit dizzy.

QUESTION

Is it harder to balance with your eyes closed?

MATERIALS

None

PROCEDURE

1. Stand on both feet in the middle of the room.

2. Try to balance for 30 seconds.

3. Close both eyes and try to balance for 30 seconds. Compare the difficulty of the two tasks.

4. Stand on one leg and balance for 15 seconds. Do not touch anything for support.

5. Close your eyes, stand on one leg, and try to balance for 15 seconds.

WHAT'S HAPPENING

Much of your sense of balance comes from your ability to see your surroundings. When you lose the ability to measure your balance with respect to the room (by closing your eyes) you have a harder time keeping your balance. People who get seasick on a boat have a similar problem. They look out at the land and water and it's all moving. Since there is no fixed point that they can look at, they lose their balance (and sometimes much more).

FOLLOW-UP

Try standing very close to a wall and repeating the experiment with one leg and both legs. This time, lightly touch the wall. Try not to use it for balance, just to remind you that it's there. Does it help you stay balanced?4

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KIDS' LAB LESSONS

QUESTION Where is my center of gravity?

EXPERIMENT OVERVIEW In this experiment you'll perform several physical tasks along with other people to determine the differences between the center of gravity of a man and a woman, as well as the differences between kids and adults.

SCIENCE CONCEPT Every object has a center of gravity. It is the part of the object that must be supported to keep from falling over. Adult men and women have different centers of gravity, as you will see. Kids, due to the fact that they have not yet physically developed like adults have, don't always show those same differences.

MATERIALS

• Adults and kids of both sexes
• Wall
• Coffee cup
• Stool

PROCEDURE Have each participant try these tasks. See who can complete them.

Test 1

1. Stand next to a wall so that one side of your body, including your foot, is touching the wall.

2. Try to lift your other foot off the ground and stay standing.

Test 2

1. Place the coffee cup 8 to 10 inches in front of your feet while standing in the middle of a room.

2. Bend over and pick up the cup.

3. Now move so that you are standing with your back and feet to a wall.

4. Place the cup 8 to 10 inches in front of you and try to bend over and pick it up.

5. Try to describe why this second task is so difficult. Repeat the original test in the middle of the room if you wish.

Test 3

1. Kneel on the floor and place the coffee cup the length of your forearm in front of your knees.

2. Place your hands behind your back and try to knock the cup over with your nose.

Test 4

1. Stand with your feet together, about 2 feet in front of a wall.

2. Have someone place a stool between your feet and the wall.

3. Lean toward the wall until your forehead is touching it. Keep your back straight while you do this.

4. Pick up the stool and hold it to your chest.

5. From this position, try to straighten your back and stand up.

QUESTIONS FOR THE SCIENTIST

• In Test 1, why do you fall immediately when you lift your outside leg?

• Try this same test in the middle of the room. Why don't you fall?

• Why are you able to pick up the cup while standing in the middle of the room, but you can't reach it with your back against the wall?

• Is there a difference in performance between men and women, or between adults and kids, for the first two tests?

• Is there a difference in performance between men and women, or between adults and kids, for the last two tests?

• Thinking about the idea of center of gravity, why do you suppose women have an easier time with the last two tests than men do?

• Kids tend to do better on these final tasks than adult men do. Can you think of a reason why this might be?

FOLLOW-UP

Think up other interesting tests you can perform to test for center of gravity.5 Also, think of jobs or sports that require good balance and a knowledge of center of gravity. Do you engage in an activity that requires you to keep your balance? If so, think about where your center of gravity is during that activity.