This post goes out to all of my friends back in Boston who are snowed in because of Nemo. If cabin fever sets in, try this activity. I’m particularly partial to it because I did it when I was a high school physics student, used it in my own classroom when I was a high school physics teacher, and may have even adapted it for one of the books I worked on as a textbook editor. As a throwback to my editing days, I’ve written up the directions in middle-school-lab-manual format.
Are You More Powerful Than a Light Bulb?
Power is a measure of how quickly something uses energy. Power is measured in watts: a 60-watt light bulb uses 60 joules of energy in one second. Are you more powerful than a light bulb? Who’s the most powerful person in your house?
- stairs (in an apartment complex or dorm, use the hall stairs and invite your neighbors to join you)
- bathroom scale
- stopwatch (who am I kidding, just use the one on your phone)
- a heavy object, such as a loaded backpack, bowling ball, or CRT
- Measure the height of one step. Multiply by the number of steps to find the height of the staircase. (Measure each step individually if you live in an old dorm in Cambridge and have reason to doubt the uniformity of your steps.)
- Weigh yourself and the heavy object that you are using.
- Have another household member time how long it takes you to run up the stairs while carrying the object. Do at least 3 trials.
- Repeat steps 2 and 3 for each household member who wants to participate.
- You need to use energy in order to do work. Work is equal to the force applied to an object multiplied by the distance the object moved in the direction of the applied force. To calculate the amount of work you did to get you + that object up the stairs, multiply the combined weight of you + the object (which was the upward force you needed to apply) by the height of the staircase (which was the upward distance that you moved). The result will be the amount of work you did- and therefore the amount of energy you used. This number will be in joules, but only if you used the right units! To convert pounds into newtons, multiply by 4.45. If you didn’t initially measure the height of the stairs in meters, shame on you.
- Power is a measure of how quickly energy is used; it is calculated by dividing the amount of energy used by the amount of time that was needed to use that energy. Average the times (in seconds!) from all of your trials. Divide the amount of energy you used by this average time. This will give you your power output in joules/sec, or watts.
- Look for the power ratings on light bulbs and appliances. Which ones are you more powerful than?
- Compare your power output with the outputs of the other members of your household. After the storm is over, who should shovel the driveway and sidewalk?