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The effect of crash forces on the shape of a plasticine cone
Introduction
Crash forces are involved when two objects collide. Newton’s laws of motion determine the
way a piece of plasticine is deformed when it crashes. As the force acts to change the
momentum, a reaction force is created which squashes the plasticine.
EXPERIMENTAL DESIGN
Variables
Independent Variable: Weight of object dropped on plasticine (grams)
We drop weights on the plasticine, and measure how much the weights weigh before we drop
them.
Dependent Variable: Amount plasticine gets squished when weights are dropped (cm)
We will measure the height of the plasticine before and after the weight has been dropped,
and calculate the change.
Control Variables:
Height of drop point of weights: We will keep this the same by designing a mechanical device
to drop the weights for us; this will allow the height to be as consistent as possible.
Height of plasticine: even though we are measuring change in height, starting with different
values for the height can influence the density, which in turn would influence the ease which
the plasticine changes height with. We will try to keep this the same by measuring the
plasticine before each drop.
Stiffness of plasticine: Changing the stiffness of the plasticine can be done by playing with it
or molding it multiple times, we do not want this to happen as this will also change how easy
it is for the plasticine to change shape, and if this changes, our results will not be as accurate
as possible. We will try to keep this variable constant by not playing with the plasticine,
keeping it as cool and unworked as possible.
Same proportions: We want the plasticine to be the same cone shape each time as changing
this could influence our results. We will try to measure the cone before each drop.
Same Piece of Plasticine: We will try to use the exact same piece of plasticine each class, as
different pieces of plasticine could have different properties, and these properties could upset
the accuracy of our results.
Research Question
How does changing the weight of the object dropped on the plasticine change how much the
plasticine gets indented?
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Hypothesis
If the weight of the object dropped on the plasticine increases, then the indentation will
increase in a linear fashion, because if the weight of the object dropped is increased, but the
height dropped from stays the same, the PGE of the object will also increase proportionately,
and as a result the force will increase. I believe the increase in force, and as a result,
indentation, to be linear because there will be nothing slowing down, or changing the force to
be non-linear during the drop; terminal velocity will not be reached, the rate of acceleration
will be the same, etc.
Apparatus
Cork bung, retort stand, weights, boss, ruler, plasticine.
Method
1. Fasten the boss to the retort stand
2. Place the cork bung directly underneath the boss
3. Form the plasticine into a cone so that it has a radius of 2 centimeters, and a height of
7 centimeters, the decrease in width should be the same over the whole cone
4. Place the cone right underneath the boss, and on the cork bung
5. Hang the weights on the boss, start off with 100 g
6. Make sure that from the top of the cone, to the bottom of the weights there is exactly
10 cm
7. Screw out the pin of the boss, until the weights drop
8. Record the decrease in height
9. Repeat steps 1-9, each time adding 100 g to the weights up to a maximum of 600g.
DATA COLLECTION AND PROCESSING
Results
Mass Dropped (g)
100
200
300
400
500
600
Decrease in Height of Plasticine (cm)
Trial 1
Trial 2
Trial 3
Average
0.4
0.4
0.3
0.36
0.6
0.5
0.6
0.56
0.8
0.9
1.0
0.90
1.2
1.0
1.5
1.23
1.5
1.5
1.6
1.53
1.7
1.9
1.6
1.73
Graphs
See separate graph on paper
CONCLUSIONS
Name
Science
Date
The data I got was surprisingly almost perfectly linear. The decrease in height was
proportionate to the increase in weight. This meant that my graph was perfectly linear with
little scatter, and no anomalous points.
In my hypothesis, I expected the relationship to be both proportional, and linear, which did
occur. For example, the average decrease in height when the weight dropped was 300 grams
was equal to 0.9, and when the weight dropped was 600 grams, the average decrease in height
was equal to 1.73. This is almost exactly double the decrease, or in other words, almost
perfectly proportional.
I believe that this is quite strange though, as I realized something when doing the experiment
that I had missed when writing my hypothesis. The fact that the plasticine was shaped into a
cone meant that the first half of a centimeter would be quite easy to push down. The second
half centimeter would then be significantly harder to push down, more impulse would be
required. The reason for this is that the width of the cone increases the lower on the cone you
go. If I am correct, this would suggest that the relationship between weight and impulse
applied is actually not linear.
When the weights get dropped, they turn the potential gravitational energy they possessed into
kinetic energy, the rate of acceleration is probably the same each trial, as factors such as air
resistance would not play a very big part on the weights as they fall. This would mean that
during all trials, the weights would have roughly the same velocity as they hit the plasticine,
disregarding how much they weigh. This also means that the only factor changing how much
energy the weights have, are how much they actually weigh themselves. This relationship
would also be proportional, since the formula for GPE is mg(h2-h1). This means that each
time, a force that is either the same, or proportional to previous trials is affecting the
plasticine, and in turn, the same, or a or proportional impulse should be affecting the cone and
the weights each time, and each time the weights should be decelerated by the same amount.
Due to the softness of the plasticine, it is incapable of resisting the weights completely, and as
a result its height decreases.
My experiment suggests that the impulse applied on the plasticine should be proportional. My
results and graph reflect this relationship. However, the fact that the plasticine was shaped
into a cone should mean that if the impulse applied was proportional, then the graph and the
decrease of height should not be.
EVALUATION
Overall, I believe that the experiment was fairly inaccurate, however for the amount of time
we spent on the experiment, and for the resources we were given for this experiment, it was
not horrible.
The biggest change we made to our experiment was the shape of the plasticine. We started off
by choosing to have it as a cylinder, this would make it easy to measure the width and height,
but we found that when we dropped the weights, the change in height was barely noticeable.
This led us to shaping the plasticine into a cone; the results were much easier to measure as
the decrease in height was much larger with a cone. However, this method was not perfect
either. Since the tip of the cone was so small, it was hard to land the weights perfectly on the
cone. This led to the cone slanting, and the change in height not being completely accurate. It
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was also hard to get the cone back to its original shape each time, harder than it was with the
cylinder.
To improve this, we could have measured the proportions of the cone more carefully,
although it’s hard to measure the angle it’s slanting at each time. More time and a protractor
would definitely be needed. To be completely sure, we could make a cast to put the plasticine
in.
Another problem we faced when executing our experiment was that the plasticine heated up.
This also meant that the plasticine got softer, and the results were not as accurate. We tried to
stay away from the plasticine when we weren’t using it, but I don’t feel it was enough. One
thing we could have done was change to new pieces of plasticine each time, but this could
also jeopardize the accuracy of our experiment, as the different pieces of plasticine could have
different density.
Our experiment models what happens when a force is exerted on another object under a small
period of time. In real life, it could be compared to a crash, car crash or any other form of
crash. Some things we did not take into account are that an object in free fall might reach
terminal velocity, or the amount of time the force is exposed to the object.
If I had been given more time to execute my experiment, a possible extension we could have
done is see how different heights we drop the weights from affect the change in height of the
plasticine. With different weights, I came to the conclusion that the change in height was
linear, would changing the drop point of the weights bring us the same results? How would
terminal velocity affect the results we got?