This week's video

Measuring Ourselves

By Marshall Brain

Scientists spend a lot of their time measuring things. They do that because that is how they gather data. For example, in another one of these videos we discovered how the temperature of ice changes when we add salt to the ice. The way that we made that discovery is by measuring the temperature of ice using a thermometer before and after adding salt.

The video talks about measuring all kinds of things about yourself and recording the data. In the video we look at three interesting measurements that you could try at home: 1) Jump height, 2) Lung capacity and 3) Reaction time.

To measure reaction time, have a friend hold a yard stick as described in the video. See how many inches the yard stick falls before you catch it. Then use this equation to calculate you reaction time:

time = SquareRoot ( distance / 0.5 * g)

[g = 384 inches / second^2]

If the yard stick falls 10 inches before you catch it, your reaction time is: sqrt ( 10 / 0.5 * 384), or 0.228 seconds.

To measure lung volume, buy some big round party balloons. Take a deep breath and blow all of that breath into a balloon. Tie off the balloon, and then measure the circumference of the balloon with a string. You can turn the circumference into a radius with the first equation, then turn the radius into your lung capacity with the other:

radius = circumference / (2 * 3.14)

volume of a sphere = 4 / 3 * 3.14 * radius ^ 3

So if the circumference of the balloon is 23 inches, the radius is 3.66 inches. The volume is:

4 / 3 * 3.14 * 3.66 * 3.66 * 3.66 = 205.26 cubic inches

205 cubic inches is 3,363 CCs, or about the volume of a 3-liter bottle of soda.

This whole measuring thing can be a lot of fun if you do it with a whole group of people and compare. Try measuring the same parameters with all of your family members, or with a group of friends, or with a classroom of students. Some of the differences can be surprising.

Also notice that many things about the body (like jump height) will improve with practice.

Use your creativity and think of all sorts of things about your body that you can measure. Have fun performing your own science experiments!