Bannhat Phat
Matt Fassbinder
Grade 8 A
9 September 2013
Bannhat's lab report of buoyancy in boat shape
Introduction
What am I testing?
I'm testing to see which boat shape does buoyancy acts most on; the shape that I will
testing are semi-sphere and cylinder.
The hypothesis
The density the object determines how the objects float; if the object is less dense than
the surrounding fluid it will float; if it's denser than the surrounding fluid, it will sink. In another
sense, if mass increases, density increases and if surface area increases, density decreases.
I deduce that my cylinder will float as it has more surface area than the semi- sphere
(14.14 cm2 for the semi-sphere: 18 cm2 for the cylinder) and has the same mass (as they both will
use the same amount of foil to construct it; 14*2). Due to this, its surface area makes it less dense
than the sphere as it's divided by the mass of the aluminum foil (which is constant for both
objects).
Procedure
Procedure for making my boats
Procedure for making my cylinder
Requirements:
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aluminum foil
protractor
ruler
pencil
scissor
tape
compass
Instruction
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Spread the aluminum foil out.
with compass draw out 2 circles with a radius of 2cm, snip them off and cut them
in half
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leave them aside
With a pencil, protractor and a ruler, measure 12 centimeters away from a corner
then mark it.
Vertically rule out a perpendicular 8 cm line from that point.
Measure 8cm away from the other side of the corner that you initially measured,
then mark it.
From that point, horizontally rule out a 12 cm perpendicular line towards the line
that was vertically drawn out.
Measure 11 cm of the 12 cm line that we drew and then mark it.
Repeat that process again on the line opposite of it, then rule out another line
connecting both sides.
Do it again on the other side
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Snip the shape out.
fold the short side in
connect and fully overlap the 1 cm gaps together
tape it together
tape the two circles to the two ends of the cylinder
Procedure for making my semi-sphere
Requirement
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aluminum foil
ping pong ball
ruler
pencil
scissor
Instruction
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It's really simple; get the ping pong ball and the aluminum foil.
Rule out and outline 8 cm*12 cm of aluminum foil.
Snip it out.
Mold and fold on the ball until it envelopes half of it.
How am I going to analyze my results from my experiment?
Firstly, the constants are equal amount of mass that will be placed on the object, equal
amount of water the object will be exposed to, equal amount of mass the objects will contain (8
cm *14 cm). The independent variable will be the surface area of the shape of the boat. The
dependant variable being the amount of mass the objects receive before sinking. Through this,
the entire load of coin that was placed on the boats until it sinks will be weighed all together as
there are different types of coins consisting of different mass.
Results
Name of shape
Semi-sphere
Cylinder
Mass
9.97 grams
13.5 grams
Area
14.14 cm2
18 cm2
Density
≈0.7051 g/cm2
0.75 g/cm2
Table 1
Table 1. The table above shows the names of my shapes, the amount of mass of coins it's able to bear
during the experiment; the area refers to the surface area the shape.
The observation
The cylinder does bear more weight than the semi sphere (3 coin or 9.97 grams: 5 coins
or ≈13.5 grams). Although the cylinder is supposed bear more weight than 5 coins, the reason
why it did it is because whenever a coin is inserted, it's directed to the other end of the boat, as it
does it sinks a little adding more water into its interior, making gain more weight, thus making it
sink. Despite that, the semi-sphere didn't tilt, but just dropped immediately after carefully being
placed with a third coin, since the coins are stacked on top of each other on one spot.
Conclusion
What I did in my testing
In the testing, the cylindrical boat, which is unstably taped together and was straightly
laid down on the water; after a third coin was tossed in, it tilted to the boat downward causing it
to spill water into the interior, because of that, the water constantly has to be drain out. For the
semi-sphere, it floats without being drained or redistributing the weight of the coins.
Did I prove my hypothesis?
The results of the data collection show that the cylinder has a higher density than the
semi-sphere (≈0.7051 g/cm2 for the semi=sphere: 0.75 g/cm2 for the cylinder). However the
cylinder was able to hold more coins than the semi-sphere (9.97 grams or 3 coins for the semisphere: 13.5 grams or 5 coins for my cylinder). Therefore proving my hypothesis right; with
constant mass of 14 cm * 8 cm of aluminum foil and different volumes, the cylinder does bear
more weight than the semi-sphere.
The reason why both boats sank in my experiment whenever a coin is added is due to
shifting of the center of gravity (the average area where weight is most concentrated in); the
center of buoyancy (the center of gravity of the volume of the displaced water) and the
metacenter (the intersection of the vertical lines of the center of gravity and center of buoyancy,
it determines the stability of the boat when tilted).
According to this, whenever a coin was placed into the cylinder, the boats tilted
downward as the coins collect at the at the bottom end. When the metacenter shifts above the
center of gravity and the center of buoyancy rises above the center of gravity, the water level
reached the opening of the boat and water starts intruding into the interior from that point.
Therefore, it becomes less stable and starts sinking downwards.
Using perspective of Archimedes principle, as the boats tilts downwards, it tilts to a
vertical position which occupies less surface area compared to the weight of the coins and water
being spilled into the ship; the density increases. Therefore making it experience negative
buoyancy.
For that reason, the boat must constantly drain out water; hence the coins must
constantly be equally distributed throughout the boat
Were the results accurate?
I think the results that I obtained were accurate; by draining the water, I got the maximum
amount of coins through which I can accurately calculate for the density of the ship at that
condition. Whenever I drained the water, there is always a residue of water adhering to the coins,
therefore adding more weight for the density of my boat, making the weight of the boat vary a
little. The water also ruined the taping of my boat, making water enter more easily as the taped
component slowly dissipates.
Work Cited
"Archimedes' principle (physics)". Encyclopædia Britannica. Encyclopædia Britannica
Encyclopædia Britannica Inc., 2013. Web. 08 Sep. 2013
Online.
<http://www .britannica.com/EBchecked/topic/32827/Archimedes-principle>.
"Floating and Stability: Center of Buoyancy." Floating and Stability: Center of Buoyancy.
N.p., n.d. Web. 07 Sept. 2013.
<http://www.planetseed.com/mathsolution/floating-and-stability-center-buoyancy>.
"Floating and Stability: Center of Gravity." Floating and Stability: Center of Gravity.
n.d. Web. 08 Sept. 2013.
<http://www.planetseed.com/mathsolution/floating- and-stability-center-gravity>.
N.p.,