Materials:
Ruler
Friend
Friend's cell phone

What To Do:
The ruler drop is a standard way to test response time, and we’ll be using it to stand in for driving in this experiment. First, you’ll need to measure your friend’s response time without any distraction. The experimenter holds the ruler near the top, ready to drop, while the subject positions their hand at the bottom of the ruler, not touching it but ready to grab at a moment’s notice. The experimenter drops the ruler and records the distance the ruler fell before the subject grabbed it, i.e., the measurement on the ruler in the exact spot where their fingers caught it. The more times you can do this, the better your measurement of response time (actually distance) will be. Make sure that your friend can’t predict when you will drop the ruler; the best way to do this is to wait a random length of time before each drop, e.g. three seconds the first time, one second the next, etc. After you have dropped the ruler at least three times, average* the measurements you’ve made to find your friend’s average reaction time, without cell phone interference.

Now things get interesting. Your friend needs to call someone on his or her cell phone and start a conversation. Once their chat is in full swing, begin the ruler drop procedure as before, again recording the measurements for each drop. Record as many drops as you did in part one, and average them together as before. Is there a difference between this number and the first one?

More:
What if your friend was watching a movie, texting (one handed) or talking to you in person? What slows response time the most? The least?

* To find the average distance, add up all the disances and divide by the number of times you measured. Ex: You did the experiment four times, and your friend caught the ruler at 5 inches, 7 inches, 8 inches, and 7 inches again. The average is (5+7+8+7) divided by 4, or 6.75.