Every time someone gets into a car to drive, they must make decisions that will keep them safe. Some of them can be made slowly, for example, whether or not to roll the window down, while others must be made very quickly, such as swerving to avoid a collision with another car.

QUESTION

What is my reaction time?

MATERIALS

Dollar bill or note card

Friend

Ruler

PROCEDURE

• Hold the dollar bill vertically lengthwise with one hand while placing your other hand's thumb and forefinger near the bottom of it.

• Drop the bill and catch it with your other hand. You should be able to do this easily.

• Now have your friend do the dropping. You should not know when the bill is to be dropped.

WHAT'S HAPPENING

When you dropped the bill, your brain was able to send a signal to your other hand telling it to start catching it. When your friend dropped the bill, you didn't have that head start, so you got a more accurate reading for your reaction time. The lower on the bill you were able to catch it, the faster your reaction time. If you weren't able to catch it at all, you aren't alone. Try dropping a ruler instead.3

FOLLOW-UP

This reaction time test is one of many you could do. See if you can come up with your own test.

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KIDS' LAB LESSONS

QUESTION What is my pulse?

EXPERIMENT OVERVIEW In this experiment you'll be measuring your pulse (heart rate) after several different activities. You'll also learn how to use different time intervals to measure your heart rate and where the best places are to find your heartbeat.

SCIENCE CONCEPT Each time your heart beats it delivers oxygen-rich blood to your body, which allows it to function properly. When you are resting, your heart rate slows down, as your body doesn't need as much blood as it does when you exercise. People who are in good physical condition are able to engage in strenuous activities while keeping their heart rate low. On your body, the strongest beats can usually be felt over your heart, in your neck just below your jaw, on the inside of your wrists, and on your thumbs.

MATERIALS Stopwatch

PROCEDURE

• Sit quietly for a few minutes before beginning this test.

• When you are ready, place your first two fingers either on your neck or on the inside of your wrist and locate your pulse.

• Once you find your pulse, start the watch and for 60 seconds, count the number of beats you feel. That is your pulse.

• Try the experiment again, but this time count for only 30 seconds. When you are done, multiply your count by two. Compare your pulses.

• Repeat by counting for 15 seconds and multiplying your count by four, then counting for 10 seconds and multiplying by six.

• Once you have determined your resting pulse, go somewhere that you can exercise vigorously for at least one minute. Exercise of this sort might include a fast jog, running stairs, skipping rope, or doing pushups. When you are done, you should be breathing hard. CAUTION: Do not exert yourself beyond what you are comfortable with. Pick an activity you can do safely.

• Choose the length of the test you wish to perform and find your pulse again.

• Compare your resting pulse with your pulse after exercise.

QUESTIONS FOR THE SCIENTIST

• What was your resting pulse?_____________

• Which result(s) did you use to come up with this number?_____________

• What was your pulse after exercise?_____________

• What are the advantages to timing for a full minute to find your pulse?___________

• What are the advantages to timing over a shorter period of time (like 10 seconds), especially when you have just finished exercising?__________________________

• The American Heart Association has determined that the maximum heart rate should be 220 minus a person's age. Was your highest rate below that number?

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FOLLOW-UP

Regular exercise can reduce both your resting heart rate and your heart rate after exercise. For a long-term study of your own heart rate, try exercising for 15 to 20 minutes daily for one month. Once a week, recheck your heart rates before and after exercise to see if they go down. If you plan on drastically changing your exercise patterns, check with your parents or your doctor to make sure the change is appropriate for you.