Laboratory 6
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The University of Tennessee, Knoxville *
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221
Subject
Geology
Date
Jun 9, 2024
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Laboratory 7: Buoyance
Manuelle Toro
mtoromar@vols.utk.edu
Purpose: For this lab we hope to test Archimedes' rule and learn about how fluid pressure works and buoyancy works. We will weigh different objects under water and find out the weight of the liquid that it displaces out of the way. This will help us figure out how dense the objects are and see if Archimedes' rule is proven to be true or false experimentally. As this rule states when an object is in a liquid, it gets a push upwards that's equal to the weight of the liquid that got pushed
out of the way, in other words describing buoyancy.
Experiment 1:
W
c
W
o
W
ow
W
cw
W
w
F
b
(F
b
-
W
w
)/F
b
Object 1
0.42N
2.64N
2.32N
0.72N
0.30N
0.32N
6.25%
Object 2
0.42N
3.42N
3.07N
0.71N
0.29N
0.35N
17.14%
Object 3
0.42N
2.40N
2.09N
0.69N
0.27N
0.31N
12.9%
Object 4
0.42N
0.88N
0.57N
0.71N
0.29N
0.31N
6.45%
m
o
m
w
V
w
ρ
o
material
Object 1
0.270
0.0306
3.06x10^-
5
8823.53
Brass
Object 2
0.349
0.0296
2.96x10^-5
11790.54
Lead
Object 3
0.245
0.0276
2.76x10^-5
8876.81
Brass
Object 4
0.0898
0.0296
2.96x10^-
5
3033.78
Aluminium
According to Archimedes' principle, the buoyant force is equal to the weight of the displaced fluid. Do your experimental results verify Archimedes' principle? Comment on your results.
o
Overall we do see this phenomenon be at play as we see that out forces are almost equal and deviate only by a small percentage with the greatest difference that being of object with a percentage difference of 17.14%
Do your experimentally determined densities of the various materials agree with the densities given in the table?
Comment on your results
o
Yes, we do see that the experimental densities taking in mind the volume and the mass of the object do relate with the literature values of the density of the objects given
.
Exploration:
As the pressure sensor is moved deeper into the liquid, how does the pressure change?
o
We see that the pleasure sensor displays, much higher-pressure levels when increasing its depth.
As liquid is added or removed from the basin, how does the pressure near the bottom of the tank change?
o
As more liquid is added we see the pressure displayed by the sensor to increase while removing has the opposite effect.
How does the pressure in the water change when the atmosphere is removed?
o
We see that when the atmosphere is removed, the decrease in pressure is significant.
Keeping all other conditions the same, does the pressure at a given distance below the surface depend on the shape of the basin?
o
Yes it does, as we can see keeping everything the same and altering the shape of the basin, either increases or decreases the
pressure depending on the shape set.
How is the density of the fluid related to the pressure it exerts?
o
We would expect to see that the denser the fluid the more pressure it will exert on the pressure meter.
How does increasing gravity change the pressure in the fluid?
o
As we increase gravity then we are increasing weight and as such a force of equal magnitude must be exerted in the opposite direction causing the pressure to significantly increase.
When g = 9.8 m/s
2
, how does pressure (in Pa) change for each meter of water depth?
o
Overall we see than when g=9.8m/s^2, for each meter descended we see an increase in pressure of about 10kPa or 0.1atm
Exercise:
(i) Lay your hands on the table in front of you and locate a bulging vein. Slowly raise your hand until it is well above your head while constantly watching that vein. What happens? What height above your shoulders do you first notice a change?
Describe your observations.
o
I have quite prominent veins on both my arms but as I raised my right arm I saw that when reaching around the same level as my nose or mouth the vein was much less prominent, and the further I raised my arm over my head the more I saw it hide under my skin
Slowly lower your hand while still watching the vein. Repeat the process. Do you have an explanation for your observations?
o
As I lower my arms I then see that the veins budges again, I can give an explanation as that as my height changes due to me raising my hands, the overall blood pressure in my arm decreases and thus the veins can decrease in size, also the rate at which blood is pumped through the veins is the same regardless, thus set rate must account for fighting against gravity and thus we can see that when my hands are raised it decreases since the rate would be enough to beat gravity but when my hands are laying on the table the rate is much greater than gravity and as such pressure is much more prominent.
(i) Lay two thick books about 10 cm apart. Place a sheet of paper on the books so that it bridges the gap between them. Try to blow the paper off the books by blowing underneath it. Describe what happens. Do you have an explanation for your observations?
o
We see that the paper does not blow away, I believe this happens because the pressure on top of the paper is much more significant than that we are providing under the sheet, as such the paper remains in the books.
Hold two sheets of paper vertically about 5 cm apart. Blow the sheets apart by blowing hard between them. Describe what happens. Do you
have an explanation for your observations?
o
We see that the sheets want to come together, we can explain this by arguing that when we blow in between them, we actually create a space of lesser pressure than that of the outside of the sheets as such the sheet pull together since that space is less pressurized than the other.
Hold a straw upright in a glass of water so that the top of the straw projects over the top of the glass. Place a second straw perpendicular to the first so that the end of the second straw is almost touching the opening of the first but is not blocking it. Blow hard through the
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second straw. Describe what happens. Do you have an explanation for your observations?
o
We see that as we blow water climbs up the straw in the water and spews out, we can argue that by blowing on the opening of the straw we create a space of less pressure as such the water rushes through the straw to that point of lesser pressure.
Reflection:
Overall, in this lab we were able to learn about the laws around pressure and the way fluids behave, most importantly we were able to verify Archimedes’ principle using experimental data, as well as see Buoyancy at work, in addition we were able to see how the density of different objects affects the displacement of water and how set object’s material could be identifies with the use of their density. Finally, this lab allowed us to put our knowledge to the test in the real world, as we worked with the things around us to create different pressure scenarios and see whether us blowing on certain areas can affect the pressure of the air in the pace we were blowing. To conclude this was quite useful in letting us learn all about pressure and how we can experimentally define its effects around us.