Lab 2: Free Fall
John Smith
Rita Cervantes (partner)
Physics 11 Lab (Monday)
Mr. Kiledjian
09/13/2006
Purpose: In this lab, we will show that an object under the influence of gravity alone
accelerates at a constant rate. We will also measure this acceleration and compare with
the actual value of 9.8 m/s2. We will also learn techniques of writing a good lab report
and forming tables, superscripts, subscripts, and Greek letters in Word.
Equipment: Demo Sparking Tape Apparatus caught on fire, wow!!!, Sparked Tapes,
Masking Tape, Two-meter stick, Calculator.
Procedure: My partner and I got a sparked tape that was already done previously and we
laid it out on the table and we put a two-meter stick on it vertically so we can read the
dots correctly. We put the 10-cm mark on the 0th dot. Then, we numbered the rest of the
dots from 1 – 24. Then, we measured the distance of each dot from the 0th dot and we
recorded this in the table. Then, we subtracted each distance from each other and then
multiplied these by 60 to calculate the average velocity in each time interval. Then, we
subtracted these velocities from each other and multiplied these by 60 again to calculate
the acceleration in each time interval. These accelerations represent the average
acceleration that the object had in each time interval, and we were hoping that these
values were close to 9.8. We noticed somewhat of a deviation in these numbers, but
when we calculated the average of these numbers, we got a number surprisingly close to
9.8!!!
Then, we compared this number to 9.8 and got a percent error.
Data Analysis: Spark Tapes were set to 60 sparks/second.
Dot Number
S (meters)
ΔS (m)
0
1
0
.004
ΝΑ
.004
Vavg (m/s)
= 60ΔS
NA
.24
ΔVavg (m/s))
ΝΑ
.06
Aavg (m/s2)
= 60ΔVavg
NA
3.6
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
.009
.018
.030
.044
.059
.079
.106
.131
.160
.194
.225
.258
.295
.334
.375
.42
.461
.508
.558
.614
.673
.736
.801
.005
∗.009
.012
.014
.015
.020
.027
.025
.029
.034
.031
.033
.037
.039
.041
.045
.041
.047
.050
.056
.059
.063
.065
.30
*.54
.72
.84
.90
1.20
1.62
1.5
1.74
2.04
1.86
1.98
2.22
2.34
2.46
2.70
2.46
2.82
3.00
3.36
3.54
3.78
3.90
.24
∗.18
.12
.06
.30
.42
−.12
.24
.30
−.18
.12
.24
.12
.12
.24
−.24
.36
.18
.36
.18
.24
.12
ΝΑ
14.4
*10.8
7.2
3.6
18
25.2
-7.2
14.4
18
-10.8
7.2
14.4
7.2
7.2
14.4
-14.4
21.6
10.8
21.6
10.8
14.4
7.2
NA
Sample Calculations for Cells with Star in Them
ΔS3 = S3 – S2 = .018 - .009 = .009 meters
Vavg3 = 60ΔS3 = 60(.009) = .54 m/s
ΔVavg3 = Vavg4 - Vavg3 = .72 - .54 = .18 m/s
Aavg3 = 60ΔVavg3 = 60(.18) = 10.8 m/s2
GexpAvg = (3.6 + 14.4 + 10.8 + …. +7.2)/23 = 219.6/23 = 9.55 m/s2
% Error = 100% x |9.55 – 9.80|/9.80 = 100% x .25/9.8 = 2.55 % !!!!!!!!!!!
Discussion: In this lab, the error came out pretty small even though the acceleration
values seemed to fluctuate quite a bit. The error could be due to several factors. First,
the object wobbles as it falls down. It begins to wobble at the beginning before it even
starts to fall, but these wobbles grow more random as it is falling due to the presence of
air friction. It also bumps into the pole and wire, so the combined effect of all these is to
cause a fluctuation of the data points. A second major source of error is that the sparking
apparatus is not necessarily consistent in how often it makes dots. Even though it is
supposed to make a spark every 1/60 seconds, it probably misses this mark and makes a
spark in too short a time or too long a time. This makes it look like it is sometimes
decelerating and then accelerating very fast. Finally, our ability to measure the location
of the dot to its actual size and the limitation of the ruler that we are using, causes another
factor of error. However, considering all these sources, our experiment still went well
and gave us only a 2.55% error!!! Possible improvements to the lab include using a
better sparking tape with more consistent spark-making ability; maybe the sparking
apparatus can come with a digital readout of how many sparks it has made and the total
time, or what the average time was between spark, then we would know the frequency of
sparks more accurately. A second improvement includes using a vernier caliper to
measure the distance between successive dots.
Conclusion: This lab proved very helpful to understand free fall. I learned that when an
object falls under the influence of gravity, its velocity increases at a regular pace and the
average of this pace is known as g = 9.8. We were able to prove this within an error of
2.55% which is still good considering the equipment we have is kind of old. I also
learned that we could conduct this kind of experiment on any planet and moon and
calculate its gravity. This might come in hand some day if I ever travel to another planet.
I also learned advanced techniques of building tables, writing equations, and putting
Greek symbols on the word document. Overall, this was a great learning experience and
an awesome lab!!! I’m looking forward to the rest of the semester.
The End