Names ______Period 1 2 3 4 5 6 7 8
LAB – Reaction Time
Prelab
Dollar bill demo: watch as you classmates perform this demo and then watch the video for further explanantion
Background:
If you drop an object from rest the distance the object falls, d, is related to the time, t, by: d = 1/2at2(where a =g)and t is the time that it takes to fall the distance d. Solving for g gives: g = 2d/t2
Therefore, it istheoreticallystraightforward to determine the acceleration of free fall simply by dropping something and measuring the time it takes to hit the ground.
Experimentally, however, it is exceedingly difficult to get precise-enough times for meaningful results. (It often turns out that the theoretically straightforward approach is exceedingly impractical in the "real world.") Over short distances (and short times), human reaction time destroys the precision of the measurement, and over long distances, air resistance becomes a factor so that the acceleration of the object is no longer constant and the calculation is invalid. These considerations (among others) are what forced Galileo to develop his famous inclined plane experiment.
The rate at which an object falls is determined by the gravitational pull of the local planet and is constant when near the surface of the planet. This principle is used by the Air Force during intake testing for pilots. In this activity, you will take this simple test to see if you would be considered for pilot training.
Purpose
1.Measure your reaction time by catching a ruler that is dropped between your fingers.
2.FYI: There is a difference between your reaction time when reacting with your hand as compared to reacting with your foot (for example, when catching an object versus moving your foot from the gas pedal to the brake as you stop a car).
Procedure
Have a partner hold a ruler by the top end as you place your index finger and thumb at the bottom (at the 0 cm mark) and prepare to catch it once released.
Snap you fingers shut as soon as you see the ruler released. Don’t try to anticipate the release.
Note where you catch the ruler.
Use the big five equation of motion, . If d (displacement) can also be written as the variable x. Then xf is final displacement and xo is original displacement. Ifvo is equal to zero and g equals the acceleration due to gravity. You can find then reset the equation to find your reaction time in seconds by solving the equation, for time.
Use the equation above to make a data table showing how far the ruler shouldfall each hundredth of a second
(xf - xo) (in cm)Time (s) / 0.13 / 0.14 / 0.15 / 0.16 / 0.17 / 0.18 / 0.19 / 0.20 / 0.21 / 0.22
Names :______Periods 1 2 3 4 5 6 7 8
Use the equation from the lab to make a data table showing how far the ruler should fall each hundredth of a second
(xf - xo) (in cm)Time (s) / 0.13 / 0.14 / 0.15 / 0.16 / 0.17 / 0.18 / 0.19 / 0.20 / 0.21 / 0.22
Now determine your and your partner’s reaction time.
PERSON 1PERSON 2
Trial 1: (xf - xo)=______reaction time = ______
Trial 2: (xf - xo)=______reaction time = ______
Trial 3: (xf - xo)=______reaction time = ______
Trial 4: (xf - xo)=______reaction time = ______
Trial 5: (xf - xo)=______reaction time = ______
Avg reaction time is: ______seconds
Questions:
1. Define free fall and explain factors that affect it.
2. If an object is thrown directly upward is it still in free fall? Why or why not? Explain.
3. What happens during each second of free fall in regards to the motion of the rate at which the object is falling? Be specific and give numerical support for your answer. (hint explain and show work for the table)
4. Graph the table you constructed in the using the following perimeters (distance on y axis and ½ at2 on the x axis). Using the skills you learned in the domino lab on graphing include the equation for the slope of the line on the graph. Hint: This is a linear relationship. Copy and paste the graph and the equation below.
5. What do you notice about the slope of the line?
6. What can you say about the rate of free fall on other planets? Why?
7. In the lab you used the equation . This is how you will see the equation should you decide to take the AP Physics 1 exam in the spring. However we write the equation as . Explain why these two equations are interchangeable for this lab purpose.
8. How is the information you gathered about reaction time in this lab going to affect future labs? In other words what new knowledge are you going to take forth with you?
9. According to the Air Force, reaction times are categorized as:
0.0 s to 0.11 s - good candidate for pilot training
0.11 s to 0.16 s - fair candidate; most likely trained as “back seat”
0.16 s to 0.20 s - preliminary training may improve reaction time; if not, transfer
over 0.20 s not even considered
Would you and your partner be a good candidate?
10. What is the maximum reading on the ruler you could have and still be a good candidate? (Show your work)
11. Explain why the dollar bill probably will not be caught in your own words with mathematical support
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