 How Fast are You?
For grades K-12 Methods
Unlike the other activities on this reflex page, this project does nottest a simple reflex. Rather, this activity is designed to measure yourresponse time to something that you see.Get a ruler (or a yardstick or candy bar). Hold the ruler near the end(highest number) and let it hang down. Have another person put his or herhand at the bottom of the ruler and have them ready to grab the ruler(however, they should not be touching the ruler). Tell the other personthat you will drop the ruler sometime within the next 5 seconds and thatthey are supposed to catch the ruler as fast as they can after it isdropped. Record the level (inches or centimeters) at which they catch theruler (you can convert the distance into reaction time with the chartbelow). Test the same person 3 to 5 times (vary the time of dropping theruler within the 5 second "drop-zone" so the other person cannot guesswhen you will drop the ruler). Here is a table to convert the distance on the ruler to reaction time.Remember that there are 1,000 milliseconds (ms) in 1 second. | Distance of catch | Reaction Time
(in seconds) |
|---|
| 2 in (~5 cm) | 0.10 sec (100 ms) | | 4 in (~10 cm) | 0.14 sec (140 ms) | | 6 in (~15 cm) | 0.17 sec (170 ms) | | 8 in (~20 cm) | 0.20 sec (200 ms) | | 10 in (~25.5 cm) | 0.23 sec (230 ms) | | 12 in (~30.5 cm) | 0.25 sec (250 ms) | | 17 in (~43 cm) | 0.30 sec (300 ms) | | 24 in (~61 cm) | 0.35 sec (350 ms) | | 31 in (~79 cm) | 0.40 sec (400 ms) | | 39 in (~99 cm) | 0.45 sec (450 ms) | | 48 in (~123 cm) | 0.50 sec (500 ms) | | 69 in (~175 cm) | 0.60 sec (600 ms) |
This reaction time experiment required visual information (the movement ofthe ruler) to travel to your brain. Then your brain sent a motor command("grab that falling ruler") to the muscles ofyour arm and hand. If all went well, you successfully caught the ruler!! Questions and Comparisons
 Test the whole class. Who is fastest?  Compare boys vs. girls. On average, arethe boys or girls faster? Compare different ages. Who isfastest?...the older students oryounger students? Compare the scores after practice.Does reaction time improve withpractice? Compare kids' scores vs. parents'scores. Who is faster? Test the whole school!! Test the whole city!!................youget the idea.
 Materials
- Ruler or yardstick or long candy bar (give the candy bar to the personwith the fastest reaction time)
CarolinaBiological Supply Company also sells a Reaction Time Ruler Setthat includes three rulers with msec gradations, oneinstruction book and recording sheets. Cost = $22.50/set. |
Reflexes 
More experiments to test your reaction times:
Pupil toPupil
Jumpto It!
Knee Jerk Reflex 
The knee jerkreflex (seen in the figure to the right) is called a monosynaptic reflex. This means that there is only 1 synapsein the neural circuit needed to complete the reflex. It only takes about50 milliseconds of time between the tap and the start of the legkick...that is fast. The tap below the knee causes the thigh muscle tostretch. Information is sent to the spinal cord. After one synapse inthe ventral horn of the spinal cord, the information is sent back out tothe muscle...and there you have the reflex. ![[email]](./gif/menue.gif)