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Ideas at Work Module 2 Measuring human reaction time The idea: Suppose you are hard at work in the kitchen making, say, an omelet, and as you reach for an egg you accidentally nudge it off the counter and it heads for the floor. How long do you have to try to catch it? Galileo discovered that everything falls alike, or at least, would fall alike if air friction did not confound its motion. For something as smooth and dense as an egg, falling for such a short distance, air friction wouldn’t matter much anyway. Not that it would help you any in the kitchen, but we can easily calculate, with precision, the time that the egg has yet to survive. The time for any object to fall from rest from a distance d is given by this equation: t = 0.072%d where d is measured in inches. If you measured in centimeters, use 0.045 instead of 0.072. The checkmark is the square root symbol. Most counter tops are 30.0 inches high, so we could find the time for the egg to fall by taking the square root of 30.0 and multiplying by 0.072. My calculator shows 0.3943602… which I would round off to 0.394 sec. We can use this concept to measure human reaction time, not with falling eggs, but with a falling ruler or yardstick. The number of inches or centimeters that the ruler falls before it is caught tells the time in the air, using this little equation and the power of physics! What you’ll need: Ruler or yardstick One to five willing volunteers Calculator or computer spreadsheet What you’ll do: Î This is the most important step: decide what interesting question you would like to answer about human reaction time. You could, for example, ask if athletes have better reaction time than us non-athletes. You could test five varsity athletes five times each, and then repeat the process with five non-athletic types. Or you could ask, do men and women have different average reaction times? Is reaction better in bright light, or dim? With loud music playing, or silence? A favorite among college students: test reaction times before and after a big party. How about left hand versus right hand? You get the idea! Choose your question, and to make it simple, have just two cases or situations. That is, if you are interested in music, compare one type of music against another, or music against silence, but don’t compare silence against four different types of music. That just gets too complicated! Ï Decide how many subjects you wish to use. Have each subject sit comfortably with his or her hand resting on the edge of a table or desk, with the thumb and index finger out over the edge, as shown. Hold the ruler above your subject’s hand so that the zero end is just between his or her thumb and finger. Instruct your volunteer to catch the ruler as quickly as possible, by pinching it as it falls, but without reaching over the edge to chase the ruler down. Drop the ruler without warning, have your subject catch it, and read the distance to the center of the fingers as accurately as you can. Record the distance fallen on the Report Sheet. Ð Repeat for a total of 50 trials, with 25 trials in each of your two test groups. Decide what you will do if the person misses the ruler altogether. You could do that one over, or use a yardstick instead of a ruler. Ñ Calculate the time for the ruler to fall, the person’s reaction time, using the equation you have already seen. In each case, round the time to three decimal places. Ò Average all 25 times for each of two cases, and again round those final results to three decimal places. Ó Answer your question about reaction time. What effect did your experimental variable have on reaction time? What conclusions can you draw? Ideas at Work Module 2 Report Sheet Measuring human reaction time Name My question about reaction time: First experimental condition: Trial Distance ,in or cm Time, sec Second experimental condition: Trial 1 2 6 2 2 7 3 2 8 4 2 9 5 3 0 6 3 1 7 3 2 8 3 3 9 3 4 Distance ,in or cm Time, sec 1 0 3 5 1 1 3 6 V Write times in the form 0.XXX, rounded to three decimal places. Times should all be lessthan about 0.250 sec. If not, please re-read the instructions and check your calculations. 12 37 13 38 14 39 15 40 16 41 17 42 18 43 19 44 20 45 21 46 22 47 23 48 24 49 25 50 Average reaction time, sec Average reaction time, sec V Be sure to enter the average times here, not the total times. My best answer to my question about reaction time:

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