Reaction Time

Students time how long it takes to catch a dropped ruler

Materials

Ruler (older kids) or yardstick (younger kids)

Directions

• Hold the ruler near the end (highest number) and let it hang down.
• Have another person put his or her hand 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 person that you will drop the ruler sometime within the next 5 seconds and that they are supposed to catch the ruler as fast as they can after it is dropped.
• Record the level (inches or centimeters) at which they catch the ruler (you can convert the distance into reaction time with the chart below).
• If in a small group: Test the same person 3 times (vary the time of dropping the ruler within the 5 second "drop-zone" so the other person cannot guess when you will drop the ruler).
• Discuss what has to happen in order for the ruler to be grabbed (the neural circuit of a reaction: eyes to occipital lobe to processing to motor cortex to muscle). Draw pathway on reaction time body diagram (see details below in discussion points).

Alternative Experiments

• Have the person catching close their eyes
  • Say "drop" when dropping the ruler
  • Or tap their foot when dropping the ruler
    How does reaction time change from having eyes open? Which method is faster/slower?
• Try the experiment in dim light. Does reaction time increase, decrease, or stay the same? Can you explain your results?
• Compare different ages. Who is faster - the older students or younger students?
• Compare the scores after practice. Does reaction time improve with practice?
• Compare kids' scores vs. parents' scores. Who is faster?

Discussion Points

• Watch this video of the activity
• Reaction time body diagram
• In the first experiment, the signal needs to pass from the eyes, to the brain, to the spinal cord and then out to the muscles
• In the alternative experiments, the signal either travels from the ear (saying drop) or from the foot (tapping the foot) before heading to the brain. 
• There are times when reaction time isimportant, such as pain reflexes, like when you step on something sharp or touch something hot

Conversion Chart

Distance on ruler		Reaction time
in	cm	sec
0.5	1.27	0.05
1	2.54	0.07
1.5	3.81	0.09
2	5.08	0.1
2.5	6.35	0.11
3	7.62	0.12
3.5	8.89	0.13
4	10.16	0.14
4.5	11.43	0.15
5	12.7	0.16
5.5	13.97	0.17
6	15.24	0.18
6.5	16.51	0.18
7	17.78	0.19
7.5	19.05	0.2
8	20.32	0.2
8.5	21.59	0.21
9	22.86	0.22
9.5	24.13	0.22
10	25.4	0.23
10.5	26.67	0.23
11	27.94	0.24
11.5	29.21	0.24
12	30.48	0.25