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# 5.3: Activities and Answer Keys

Difficulty Level: At Grade Created by: CK-12

## Activity 4-1: How Fast Is Your Reaction Time?

### PLAN

Summary In this activity students measure their reaction time and consider the mechanisms that allow for quick reactions.

Objectives

Students:

\begin{align*}\checkmark\end{align*} measure the ir reaction time.

\begin{align*}\checkmark\end{align*} explain the changes in their reaction time.

\begin{align*}\checkmark\end{align*} describe the advantage of a fast reaction time.

Student Materials

• 20 cm ruler
• Activity Report

Teacher Materials

Estimated Time

One 50-minute period

### IMPLEMENT

Steps 1-2 You may want to have students repeat the procedure using their other hand. Students can record the time in seconds for each trial.

Step 3 Students should switch roles. Again, you may want to have students repeat the procedure using their other hand. Students can record the time in seconds for each trial.

Step 4 Have students graph their results.

Each student team needs a 20 cm metric ruler.

Be sure students know how to construct a graph from their data.

Extend Activity 4-1 by having students determine their reaction times to various stimuli. Several ways to test reactions times are described below.

Hand Slap-Both members of student pair removes all jewelry from wrists/hands. One student holds the right hand out with the palm facing up. The partner rests his/her right hand on the partner's right hand with the palm facing down. The first student (palm facing up) attempts to turn his or her hand over fast enough to slap the back of the partner's hand (palm facing down). The hand turning speed of one partner is tested against the partner's reaction time.

Penny Grab-Students hold their right arm out with the palm facing down. A penny is placed on the center of the back of the hand. Students slowly tilt their hands to the side so that the penny slides off. Students try to catch the penny before it hits the ground. The procedure is repeated and the number of catches is documented. Students should determine whether their reaction time gets better with practice. The same procedure can be repeated with the left hand.

Dollar Drop-One student holds a dollar bill (on its side) at arm's length above his/her head. Another student attempts to catch the dollar as it flutters to the ground. (Restrict student to one hand if this is too simple.) Have students predict whether it would be easier to catch a tennis ball or the dollar. Students should discover that it takes time for the eye to see that the dollar was released, time for the brain to tell the hand to grasp it, and more time for the hand muscles to respond. This activity illustrates that the brain and nervous system must have time to adjust before most movements can be accomplished.

### ASSESS

Use the completion of the activity and the written responses to the Activity Report to assess if students can

\begin{align*}\checkmark\end{align*} measure their reaction time.

\begin{align*}\checkmark\end{align*} explain the changes in their observed reaction times.

\begin{align*}\checkmark\end{align*} describe the advantage of a fast reaction time.

## Activity 4-1: How Fast Is Your Reaction Time? – Activity Report Answer Key

• Sample answers to these questions will be provided upon request. Please send an email to teachers-requests@ck12.org to request sample answers.
1. Record in the table below the reading on the ruler for each trial.
Trial Distance in centimeters
1
2
3
4
5
6
2. Graph your results recorded in the table above.
3. Using the data in your table and graph, what was the trend in reaction times recorded? Compare the times from the first to the last trials. What would you expect after ten trials?
4. How would you explain the changes in reaction time?
5. What are some advantages of fast reaction times?

A suggested response will be provided upon request. Please send an email to teachers-requests@ck12.org.

What happens when someone throws a ball at you and you blink? Trace the path the message takes through your nervous system.

• Sample answers to these questions will be provided upon request. Please send an email to teachers-requests@ck12.org to request sample answers.
1. What is a reflex response to a stimulus? Give three examples, describing both the stimulus and the reflex.
2. Name the five parts of a reflex in order.
3. What is the difference between a sensory neuron and a motor neuron?
4. If you touch a hot stove, why do you pull your hand away before you feel pain?
5. What role does an inhibitory interneuron play in a reflex?

## Activity Report 4-1: How Fast Is Your Reaction lime?

1. Record in the table below the reading on the ruler for each trial.

Trial Distance in centimeters
1
2
3
4
5
6

2. Graph your results recorded in the table above.

3. Using the data in your table and graph, what was the trend in reaction times recorded? Compare the times from the first to the last trials. What would you expect after ten trials?

4. How would you explain the changes in your reaction time?

5. What are some advantages of fast reaction time?

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