1 Free-fall Object: Reaction Time, Physics Grade X SMA IBC 1st sem., 2015-2016 Devilim, S.Si.

EXPERIMENT: REACTION-TIME Aim: In this experiment, use what you know about falling object to measure reaction time Theory: Free falling object falls through a distance of : where d is distance, t is the time, and g is 9.80 m/s2. Gravity is pulling down on the ruler at a constant rate. The longer it falls, the faster it goes. By measuring how far the ruler falls, we can calculate the speed at which it is moving and the time it took you to catch it. Materials and Tools: 1. ruler (50 cm) Procedure: 1. Hold the index finger and thumb of your dominant hand about 2.5 cm apart, and

then have your friend hold a ruler vertically in the space between your finger and thumb (as shown in figure A2.2).

2. Note the position of the ruler relative to your index finger. 3. Without warning your friend should let go of the ruler, and you should try to

catch it with your fingers as quickly as you can (without moving your hand downward).

4. Notice what cm-mark your fingers are on when you catch the ruler. Note the final position of your fingers after you get hold of the ruler.

5. Repeat the measurement of the distance for 5 times. 6. Average the results of distance, then calculate the value of average time taken using equation from the

theory. That average time is your average reaction time. Experimental Data value of gravity = 9.80 m/s2 Your name : Age :

Trial 1 2 3 4 5 Average value Initial position /cm Final position /cm

Distance /cm Calculation of your reaction-time: Average value of your reaction-time: s Results & Discussion 1. Why do you think it takes time for your fingers to react when your eyes see the stick start to fall?

2. Compare your reaction-time with your friends’ reaction-time. Do both of you have the same value? Give possible reason(s) as for why it could happen. Yes / No,

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2 Free-fall Object: Reaction Time, Physics Grade X SMA IBC 1st sem., 2015-2016 Devilim, S.Si.

3. Do this experiment with adult (it could be your parent or someone older than you).

Record his/her data in the table below and find his/her reaction time. Experimental data value of gravity = 9.80 m/s2

Name of adult: age : Trial 1 2 3 4 5 Average value

Initial position /cm Final position /cm Distance /cm Calculation:

Average value of reaction-time: s

Compare his/her result with your reaction time. Who is quicker? What do you think the reasons why reaction time might be different for an adult and a child?

4. Explain one benefit of knowing human’s reaction time in daily life.

Conclusion: