5. Give examples where reaction time is important in sports. EQUIPMENT AND SUPPLIES: Dollar Bill (Best if clean with no creases) 30 Centimeter Ruler (use a plastic 30cm ruler or if you download a ruler print or paste it on heavy cardboard http://www.vendian.org/mncharity/dir3/paper_rulers/ ) Stopwatch (cell phone, stopwatch or online http://www.online-stopwatch.com/) DISCUSSION: Reaction time is the time interval between receiving a signal and acting on it for example, the time between a tap on the knee and the resulting jerk of the leg. Reaction time often affects the making of measurements, as, for example, using a stopwatch to measure the time for a 100m dash. The watch is started after the gun sounds and is stopped after the tape is broken. Both actions involve the reaction time. PROCEDURE: Step 1. Hold a dollar bill so that the mid-point hangs between your partner's fingers. Challenge your partner to catch it by snapping his or her fingers shut, without moving the rest of the hand, when you release it. Also, have your partner hold the bill in the same way and see if you can catch it when it is released. What do you discover? Now try using a ruler, line up the zero centimeter with the top of the fingers. Let the ruler fall and your partner catch it as before. Read off the centimeter from the top of the fingers. The distance the ruler will fall is given using 12 t = = 2d g 2 980 -0.045 a d=81 since we measured distance we rearrange the equation to give us the time of fall in seconds t = t = 2d g 2 980 - t = 0.045 for d in cm and t in seconds we use g=980cm/s TRIAL TRIAL 2A TRIAL 3A TRIAL 1B TRIAL 2B TRIAL 3B 1A STARTING POINT 0 cm 0 0 cm 0 cm 0 cm 0 cm ENDING 23 cm 22 cm 24 cm 27 cm 28 cm 26 cm POINT DISTANCE 23 cm 22 cm 24 cm 27 cm 28 cm 26 cm TRAVELED Step 2: You and your partner will now take turns dropping a centimeter ruler between each other's fingers. Catch it and record the number of centimeters that passed during the reaction time it took each of you to catch the ruler each time. Each of you drop the ruler three times. Then calculate your reaction time using the above equation for t with d in centimeters. TRIALIA TRIAL2A TRIAL3A TRIAL1B TRIAL2B TRIAL3B STARTING POINT ENDING POINT DISTANCE TRAVELED PARTNER A AVERAGE DISTANCE TRAVELED FOR THREE TRIALS PARTNER B AVERAGE DISTANCE TRAVELED FOR THREE TRIALS CALCULATE THE REACTION TIME USING THE AVERAGE FOR THE THREE TRIALS. SHOW YOUR CALCULATIONS PARTNER A REACTION TIME PARTNER B REACTION TIME SUMMING UP: 1. Do you think your reaction time is always the same? Is your reaction time different for different stimuli? 2. Suggest possible explanations why reaction times are different for different people. 3. Do you think reaction time significantly affects measurements you might make when using timers for this course? How could you minimize its role? 4. What role does reaction time play in applying the brakes to your car in an emergency situation? Estimate the distance a car travels at 100km/hr during your reaction time in braking.