Name:________________________
Period:___________
Date:______________
Part 1: Free-Fall
[Lab 6]
Points: ____________ / 100
Objective: Using the available materials (metersticks, tape, rulers, stopwatches, tennis ball), design a
procedure that will allow you to calculate an experimental value for the acceleration due to gravity. Perform
three trials to obtain an average value. Your average value must be within 30 % error.
Procedure (include a diagram):
Outline of Procedure:
Data:
Trial
1
2
3
Additional Information pertaining to data:
Diagram of Set-Up (including measurements made):
Calculations and Results:
Result: Average acceleration due to gravity = _________________________________
Percent Error
Discussion of your results (What caused your percent error? Why did you not obtain ‘perfect’ results? Etc):
Part 2: Reaction Time
Background
So, you think you’re quick? It is very hard to measure small amounts of time accurately. You have experienced
this in trying to make accurate measurements of time using a stopwatch in previously labs. In order to determine our
personal reaction time, which is typically a fraction of one second, we will apply physics.
In this lab, we will put what we know about freely-falling objects to the test. According to the findings of
Newton and Galileo, all objects fall to Earth with the same acceleration: - 9.8 m/s2, known as the acceleration due to
gravity. Therefore, a ruler falling between our fingers will accelerate at this rate until it is stopped by our grasp (or the
floor!). We can use the Galilean/Kinematics equations to determine how quickly it takes each one of us individually to
respond to, and grab, a falling object.
Part A: React!
Procedure
1. Have a partner hold a ruler so that the 0.0 cm mark is in between your thumb
and fingers, as shown in the picture to the right. [Sometimes it is easier to use your
forefinger instead of all fingers. Do a few trials for each method.]
2. Without warning, your partner will drop the ruler. Make sure the ruler is not
hitting or touching your fingers in any way. NO HINTS OR WARNINGS; THAT’S
CHEATING!!
3. Close your fingers and thumb as soon as you realize the ruler is falling and catch
the ruler as quickly as you can! Each person will have a different reaction time and
therefore will all catch the ruler at a different position.
4. Record the number under your thumb as “Distance Fallen”. You will have to
estimate the distance to one decimal place and convert to meters (example: 11.5
cm is recorded as 0.115 m).
5. Repeat steps 1-4 for a total of 3 distances for EACH partner.
6. Calculate the ‘fall’ time of the rule; this is your “Reaction Time”.
Show Work For 2 Trials:
Partner 1: __________________
Trial
Distance
Fallen
(m)
Reaction Time
(s)
Partner 2: __________________
Distance
Fallen
(m)
1
2
3
Average
Average
Reaction Time
(s)
Part B: Make a Decision!
Suppose you not only had to react to a situation, but also had to make a decision about that situation. For example, as
you approach an intersection, the light changes from green to yellow. You must make a quick decision regarding
whether to slow down or maintain speed.
Procedure
1. You will use the same procedure as in Part 1 for this section, but with one twist: when one partner drops the ruler,
he/she will say either “RED” or “GREEN”. If he/she says “RED”, catch the ruler. If he/she says “GREEN”, let the ruler fall.
You must obtain 2 “RED” catches. If you catch on “GREEN”, you must ERASE your last “RED” time!
Show Work For 2 Trials:
Partner 1: __________________
Trial
Distance
Fallen
(m)
Reaction Time
(s)
Partner 2: __________________
Distance
Fallen
(m)
Reaction Time
(s)
1
2
Average
Average
Analysis
1. By how many times greater is your average reaction time when you need to make a decision compared to your
normal reaction time? (ratio of: Decision Reaction Time / Normal Reaction Time )
Part C: Reaction Ruler
On the strip of paper provided, you must design Reaction Time Ruler that is, a ruler with measurements of reaction time
as opposed to measurements of distance. The goal is for a person to catch the falling ruler and determine their reaction
time without making calculations. Specific Guidelines include:
1. The time of 0.0s must be designated as the bottom of the ruler.
2. Each time must correspond to the equivalent fall distance and be measured from the bottom of the ruler.
3. You must include the following as measurements: (a) Your average reaction time, (b) your partner’s average reaction
time, (c) a reaction time corresponding to the mid-point of the ruler, (d) a reaction time corresponding to the top of the
ruler, and (e) a reaction time corresponding to the human average of 0.16s.
Name:________________________
Period:___________
Date:______________
Extension: Get Rich Quick…
(HW)
This assignment will be collected and graded as a homework
assignment, based on correctness.
Points: ______________ / 10
Challenge your friends and family to steal your money. Have your friend(s) or family hold out
their forefinger and thumb. Place a dollar bill in between their outstretched finger and thumb
so that George’s face is directly behind the thumb (similar to how you positioned your fingers
near the 0.0 cm mark on the ruler). Without warning, drop the dollar. Can anyone catch it?
1. Write a brief paragraph describing your results. Was anyone able to catch the dollar?
2. Calculate what a person’s reaction time would have to be in order to perform this task.
You may need to make some measurements in order to perform this calculation!