Galileo Projectile Motion Experiment Lab Report
Pinia
Group: Angela, Dimas, Tommy
Introduction:
When an object free falls, it only has a vertical component, since it’s direction is
only vertical. When an object is rolled on a table on a straight line, it only has a
horizontal component, since it would only move horizontally. Projectile motion
is a non-linear motion, which means it creates a curved path. It contains both
horizontal and vertical components that are each independent and not affecting
the other. When we create a projectile path that accelerates in the vertical
direction only, and having a constant horizontal velocity, the shape would be a
parabola (especially if air resistance is small enough to just not include in the
equation). They are all also affected by gravity. In this experiment, we are
looking at the parabolic shape an object creates when it is projected, and how
different things affect the distance an object covered.
Research Questions:
Does the initial velocity affect how far an object will go?
Does the angle/height of the start of the ramp affect how far an object will go?
What affects a parabolic motion?
Can/how do we relate the equations for parabolic and linear motion to actual
objects?
Objective: To observe the path where the marble falls (parabolic motion) and
the relation between velocity and distance.
Hypothesis:
 The bigger the velocity, the distance of where the marble touches the
ground will increase.
 The bigger the angle (which means the higher the starting height), the
distance of where the marble touches the ground will first increase then
eventually would decrease.
 The higher the speed, the distance of where the marble touches the
ground will increase.
 Parabolic motion will happen when we throw a marble because we throw
a marble with horizontal and vertical velocity, but then there is gravity.
Variables:
Independent:
 For experiment 1.
Horizontal distance
 For experiment 2.
Horizontal distance
 For experiment 3.
 For experiment 4.
Horizontal distance
 For Experiment 5.
Height of the ramp
Dependent:
 For experiment 1.
Time to reach the ground
 For experiment 2.
Parabolic motion
 For experiment 3.
Parabolic motion
 For experiment 4.
Distance to reach the ground
 For Experiment 5.
Distance to reach the ground
Control: the length of the ramp, the height of A to B
Materials:
Ink
3 big papers
Equipments:
5 marbles
Tennis ball
Camera
Measuring tape
Ruler
Pencil
Ramp
Tables to support the ramp
Method:
First, set up the ramp, using two support points (DF and EG). Measure what you
have. (Height of table, length of the ramp, length of the suspensions, etc. (like
shown in the diagram))
For experiments one and two:
A to B: 71 cm
B to C: 97 cm
C to D: 153 cm
C to E: 303.5 cm
D to E: 150.5 cm
E to G: 58 cm
D to F: 30 cm
For experiments four and five:
A to B: 84 cm
B to C: 97 cm
C to D: 153 cm
C to E: 303.5 cm
D to E: 150.5 cm
Experiment four: E to G: 63 cm
Experiment five: E to G varies
1. Experiment 1
a. For experiment number one, we need two marbles.
b. Person A will hold one marble, person B will hold the other
marble, while person C needs to be ready at the end of the ramp to
observe the sound that will be made by the marbles.
c. Person A will have their marble set at point E, and person B’s
marble will stand close enough to point B.
d. When the marble from point E reached point B, person B must
release the marble from point B, and person C needs to listen
carefully if the sound of both marbles hitting the ground is at the
same time.
e. Try this with different points for the marble of person A. (e.g. point
D)
2. Experiment 2
a. Next, we will need about five marbles.
b. We will have someone hold a big piece of paper is preferably a
color that makes the ball look clearer. The person will make the
paper act as a background and stand beside the ramp.
c. Have one other person take a video of the whole process.
d. We release the marbles on the ramp in such a way (either all at
once, or giving one second gaps, etc.) that when the marbles create
a parabolic motion, they all follow the marble in front of them very
closely so that the camera can get a picture of five or so different
marbles in the same picture creating a parabolic motion path that
can be apparent if we stop the video at one point.
3. Experiment 3
a. For the third experiment, have two people throw a tennis ball back
and forth while taking a video of it, so we can analyze the parabolic
motion with tracker.
4. Experiment 4
a. For the fourth experiment we will need a marble, some ink, a big
paper, a ruler/measuring tape, and something to write with.
b. Put the big paper on the ground at the end of the ramp.
c. Use a ruler to make sure it start just where the ramp ends, or if you
don’t, make sure you make a line where the ramp ends with a
pencil. This is so you can measure how far the marble is from the
ramp when it landed on the paper.
d. Write points on the ramp with a pencil (each 20 centimeters apart
from the other, the first one 20 centimeters from the top of the
ramp.).
e. Cover the marble with ink and release it from the first point. Make
sure you have someone to watch where the marble landed on the
paper, and where it made a mark.
f. Measure how far that is from the ramp with a ruler/measuring
tape. Take notes of what you measured.
g. Repeat this step three times with the same point (apply more ink
on the marble each time or whenever necessary so that it would
still live a mark on the paper).
h. Once done with that, move on to the next point. Repeat the
experiment three times for each point.
Data Collection and processing:
1. Whether we release the marble at point B or D, the marble with both
vertical and horizontal motions and the marble with only vertical motion
will both reach the ground at the same time.
If we see from the data I got from tracker, both marbles reached the ground at a
slightly different time, but that might be an error because we released the ball
manually and maybe our reflexes aren’t that accurate.
2. They do make a semi-parabolic motion.
3. The tennis ball does create a parabolic motion.
4. O
Horizontal
f
distance
(how far up
w
the ramp?)
e
Trial 1
distance
Trial 2
distance
Trial 3
distance
Average
5.
283.5 cm
263.5 cm
243.5 cm
223.5 cm
203.5 cm
94 cm
92.7 cm
96.8 cm
90 cm
86.5 cm
90 cm
91.5 cm
97.2 cm
91.2 cm
88.9 cm
95.8 cm
96.5 cm
97.1 cm
91.1 cm
86.3 cm
93.267 cm
93.567 cm
Vertical
Distance (how
high is the
first point of
the ramp?)
Trial 1
distance
Trial 2
distance
Trial 3
distance
Average
97.033 cm
90.767 cm
87.233 cm
81 cm
69 cm
65.3 cm
54 cm
122.5 cm
115.5 cm
103 cm
104 cm
124 cm
117 cm
118.5 cm
110 cm
125 cm
118 cm
119 cm
112 cm
123.833 cm
116.833 cm
113.5 cm
108.667 cm
Data Analysis
Experiment 1.
It turns out that both still reached the ground at the same time, since the sound
of them hitting the ground was at the same time. Even though we moved the
starting point and the distance changed, the time taken to reach the ground for
the marble that have both horizontal and vertical motion, and the time taken for
the marble that have only vertical motion when released from the same point at
the same time will be the same. There might be a slight difference, but for that
we if it is only a slight difference, it might be some error caused by not accurate
reflexes.
Experiment 2.
We released the marbles quite closely to each other so that we can get a few
marbles following each other in a parabolic motion in the camera. They do make
a semi- parabolic motion when released from the ramp (because a parabolic
motion will only be made if we throw a marble and not just release it from a
ramp.)
Experiment 3.
Here we have a tennis ball that is thrown by two people (Tommy and Dimas)
back and forth. Tracker analyzes the data and the results are that we can see a
parabolic shape in the path of the tennis ball. By observing the patterns and how
Tommy/Dimas throw the ball, I saw that the parabolic shape could change if they
change the way they throw the tennis ball. Sometimes it’s the initial velocity;
sometimes it’s the direction. When the person increase the initial velocity the
tennis ball will go straighter for a longer amount of time. The direction/angle
changes direction of the parabolic motion.
With the same angle,
Less initial velocity:
More initial velocity:
With the same initial velocity,
Smaller angle:
Bigger angle
Experiment 4.
As we release the marble closer to the end of the ramp, and so have less initial
velocity, the distance of the marble increased then decreased. For each try, we
decreased 20 centimeters in horizontal distance from the last point. We started
with a point 20 centimeters from the top. For the first three points, the distance
where the marble hit the ground increased, then it suddenly decreased for the
last two points. This might be because until the third point, the initial velocity is
roughly the same, but the marble gets closer to the end every time, meaning that
it will lose less initial velocity. Then for the last two points, it gets to a point
where the initial velocity decreases significantly.
Experiment 5.
As we decrease the height of the ramp, which means we decrease the angle, and
will have less initial velocity, the distance decreased as well. In overall, it kept on
decreasing, which proves that it the lower the starting point, the smaller the
angle, the less initial velocity, the less the distance of where the marble touches
the ground.
Evaluation
(Reliability (trials + values), Anything that affects results & how can we fix
them)
In overall, the results my group had should be quite reliable, because for each
experiment we had more than one trial for each situation. Although we
could’ve had more trials/points, especially for the last experiment (we only
have four points because there wasn’t enough time), we still tried all more
than once. Things that might affect the result include the specific weight of the
marbles (they might vary a bit, and not all be completely identical although
they look like they are). The difference of results may not be significant, but it
still would cause me to have a less accurate result. We might have to try
weigh the marbles first next time. Another factor that could affect the results is
the air resistance. Theoretically, formulas are made so that they do not
include the air resistance, and so will only be roughly correct. In real life, air
resistance does exist and it might make the marble move from its path. I don’t
think we can eliminate air resistance all at once, but avoiding outdoors (where
the wind can be unpredictable) or moving too much during the experiment
might help. For the first experiment, since we might not be standing equally
between the places both marbles will fall on, it might affect the sound of them
hitting the ground that I hear. The difference must be very small, but it doesn’t
hurt to try and be as in between both marbles as can be next time. Also, since
we’re releasing the marbles manually, if our reflexes aren’t that fast, the
marbles might be released from the point the ramp ends at slightly different
times, which might result in a slightly different result. For the third experiment,
we didn’t use a tripod, but put the camera on a bench instead. Although it’s
quite stable, it might not be as stable/accurate as if we’re using a tripod.
The straight line: initial velocity/speed. Equation:
The curved line shows the parabolic motion. Equation:
Shows the points where the object is every second.
Conclusion:
To conclude, we can say that the bigger the velocity, the distance of where
the marble touches the ground will not always increase. This was proven in
experiment four. The distance between the starting point and the end of the
ramp also matters. The bigger the angle, the further the marble will go,
because the distance from the starting point to the end of the ramp didn’t
change. This was proven in experiment five. In my hypothesis, I got the
results for changing the velocity and the angle mixed up. The higher the
speed, the distance of where the marble touches the ground doesn’t always
increase, as proven in experiment four. Parabolic motion does occur when we
throw something in the air, but that parabolic motion itself is not constant and
can change (although remaining a parabolic motion.)
Further research:
For further research, we can try different types of marbles/balls. We can also
have an experiment to observe air resistance (by using something that would
create a big enough air resistance that will be noticeable in the results). We
can try observing things in a no-gravity room, but it would be difficult to find
one near us that is affordable for a school experiment.
MLA:
Hewitt, Paul G. Conceptual Physics: the High School Physics Program. 3rd ed.
Menlo Park, CA: Addison-Wesley, 1997. Print.