DEPARTMENT OF PHYSICS
FACULTY OF SCIENCE & MATHEMATICS
UNIVERSITI PENDIDIKAN SULTAN IDRIS
SEMESTER 2 SESI 2018/2019
ASSIGNMENT
SFU 1013 BASIC PHYSICS 1
Title: BUOYANCY
NO
NAME
MATRIC NUMBER
1
NOR AKIDAH BT ABDULLAH
E20181019935
2
AISWARIA A/P RAMALINGAM
E20181020034
3
SHIVYA MALNEE A/P THAMILVANAN
E20181020036
4
ADAM HAIRIZH BIN SIHAIRIZH
E20181019950
LECTURER : DR. THO SIEW WEI
DATE OF SUBMISSION: _____________________
PLANNING AND CARRYING OUT INVESTIGATIONS
Introduction
Archimedes’ principle, physical law of buoyancy, discovered by the ancient Greek mathematician and
inventor Archimedes, stating that anything that completely or partially submerged in a fluid (gas or
liquid) at rest is acted upon by an upward, or buoyant, force the magnitude of which is equal to the
weight of the fluid displaced by the body (HaileyBury, 2016). The volume of displaced fluid is
equivalent to the volume of an object fully immersed in a fluid or to that fraction of the volume below
the surface for an object partially submerged in a liquid. The weight of the displaced portion of the fluid
is equivalent to the magnitude of the buoyant force. The buoyant force on a body floating in a liquid or
gas is also equivalent in magnitude to the weight of the floating object and is opposite in direction; the
object neither rises nor sinks.
For example, a ship that is launched sinks into the ocean until the weight of the water it displaces is just
equal to its own weight. As the ship is loaded, it sinks deeper, displacing more water, and so the
magnitude of the buoyant force continuously matches the weight of the ship and its cargo.
If the weight of an object is less than that of the displaced fluid, the object rises, as in the case of a block
of wood that is released beneath the surface of water or a helium-filled balloon that is let loose in air.
An object heavier than the amount of the fluid it displaces, though it sinks when released, has an
apparent weight loss equal to the weight of the fluid displaced. In fact, in some accurate weighings, a
correction must be made in order to compensate for the buoyancy effect of the surrounding air.
Liquid exerts a force on objects immersed or floating in it. This force is equal to the weight of the liquid
that is displaced by an object (Anthony Smith, 2019). The unit for the buoyant force (like other forces)
is the Newton (N). The formula for buoyant force is ( Fb = ρgV = ρghA) where the (density of liquid)
(gravitational acceleration) (volume of liquid) = (density) (gravitational acceleration) (height of liquid)
(surface area of object).
PROBLEM STATEMENT
Since the density of iron is much higher than the density of the sea water, why does a
ship made of iron still float on the surface of the sea?
You cannot walk on the water, you’re too heavy and you’ll sink like a stone. But this
aircraft carrier can float, even though it is over 300 m long, at least a million times heavier
than you are and carriers about 70 airplanes and 4000 sailors. Ships, large oceangoing
vessels and boats, smaller ones are a brilliant example of how science can be put to work to
solve a simple problem. All boats can float, but floating is more complex and confusing than
it sounds and it's best discussed through a scientific concept called buoyancy which is the
force that causes floating. Any object will either float or sink in water depending on its
density, how much a certain volume of it weighs. If it's more dense than water, it will usually
sink; if it's less dense, it will float. It doesn't matter how big or small the object is. For
example, a gold ring will sink in water, while a piece of plastic as big as a football field will
float. The basic rule is that an object will sink if it weighs more than exactly the same volume
of water.
We are presented with a challenge question that they must answer with scientific and
mathematical reasoning. The challenge question is: "You have a large rock on a boat that is
floating in a pond. You throw the rock overboard and it sinks to the bottom of the pond. Does
the water level in the pond rise, drop or remain the same?" We observe Archimedes' principle
in action in this model recreation of the challenge question when a stone is placed in a
container of water and a the water displace. We use terminology learned in the classroom as
well as critical thinking skills to derive equations needed to answer this question.
(Next Generation Science Standards (NGSS).)
Aim
To investigate the relationship between the buoyant force acting upon an object in a liquid and the
weight of the liquid displaced.
Hypothesis
Our hypothesis on Archimedes' principle is accepted. Archimedes Principle states that the buoyant force
on an object in a fluid is equal to the weight of the volume of fluid it displaces. This explains how even
massive ships stay afloat while the ship is a very heavy object. Archimedes Principle was represented
by the following experiment.
Apparatus and materials

Retort stand

Eureka can

Beaker

Measuring cylinder

String

Spring balance

3 stones (with different mass)
Variables

Manipulated variable : Weight of stones

Constant variable : Density of liquid used

Responding variable : Buoyant force / weight of liquid displaced
Procedures
1. The apparatus was set up.
2. The eureka can was filled with water on the retort stand.
3. The string was tied at the end of the hook of spring balance.
4. One of the stone was tied at the another end of the string.
5. The weight of the stone was measured and recorded.
6. The tied stone was immersed into the eureka can slowly.
7. A beaker was put beside the eureka can so that the water from the eureka can will be displaced into
the beaker.
8. The water from the beaker was transferred into a measuring cylinder.
9. The volume of water displaced was observed and recorded.
10. Total of three trials were done for each stone.
11. The experiment was repeated with another two stones.
DEVELOPING AND USING MODELS
(Figure 1 : Physics of Ships at Sea. (2014, January 21). Retrieved from
(http://passyworldofphysics.com/phyics-of-ships-at-sea/ )
(Figure 2 : LadyNiel, M. (2008, August 30) Retrieved from
https://maryladyniel.weebly.com/1--submarine.html )
(Figure 3: Brisbane,2009, Flight Info. Retrieved from
https://www.brisbanehotairballooning.com.au/how-hot-air-balloons-fly/)
ANALYSING AND INTERPRETING DATA
Mass of the stone (g)
4.0g
6.0g
26g
Number of trials
1st
2nd
3rd
1st
2nd
3rd
1st
2nd
3rd
Apparent mass of
the stone submerged
in water (g)
1.0
1.1
1.0
2.0
2.0
2.2
12.0
12.1
12.3
Volume of water
displaced (𝑐𝑚3 )
1.5
1.3
1.3
3.0
3.2
3,2
13.0
13.0
13.3
Density (𝑔/𝑐𝑚3 )
2.0
2.2
2.3
1.3
1.3
1.2
1.1
1.1
1.0
Average density 𝑔/
𝑐𝑚3
2.2
1.3
Table show that the data of mass of drinking bottles and force applied
Plot a graph of mass of the stone (g) against average density, g/𝒄𝒎𝟑
1.1
From the graph, as the mass of the stone (g) increases the average density of the stone (𝑔/𝑐𝑚3 )
decreases. For 4.0g of stone the average density is 2.2 (𝑔/𝑐𝑚3 ). While for 26.0g of stone has
average density of 1.1(g/𝑐𝑚3 ). Hence,it is proven.
Data analysis
To calculate the density of the stone by using this formula :
𝐦𝐚𝐬𝐬 𝐨𝐟 𝐭𝐡𝐞 𝐬𝐭𝐨𝐧𝐞(𝐠) − 𝐚𝐩𝐩𝐚𝐫𝐞𝐧𝐭 𝐦𝐚𝐬𝐬 𝐨𝐟 𝐭𝐡𝐞 𝐬𝐭𝐨𝐧𝐞 𝐬𝐮𝐛𝐦𝐞𝐫𝐠𝐞𝐝 𝐢𝐧 𝐰𝐚𝐭𝐞𝐫(𝐠)
𝐯𝐨𝐥𝐮𝐦𝐞 𝐨𝐟 𝐰𝐚𝐭𝐞𝐫 𝐝𝐢𝐬𝐩𝐥𝐚𝐜𝐞𝐝 (𝐜𝐦𝟑 )
Calculations :
Density of the stone at 4.0g :
First trial :
4.0𝑔−1.𝑜𝑔
1.5𝑐𝑚3
Second trial :
Third trial :
= 2.0𝑔/𝑐𝑚3
4.𝑜𝑔−1.1𝑔
1.3𝑐𝑚3
4.0𝑔−1.0𝑔
1.3𝑐𝑚3
= 2.2𝑔/𝑐𝑚3
= 2.3𝑔/𝑐𝑚3
Average density for stone at 4.0g =
= 2.2𝑔/𝑐𝑚3
2.0𝑔/𝑐𝑚3 + 2.2𝑔/𝑐𝑚3 +2.3𝑔/𝑐𝑚3
3
Density of the stone at 6.0g :
First trial :
6.0𝑔−2.0𝑔
3.0𝑐𝑚3
Second trial :
Third trial :
= 1.3𝑔/𝑐𝑚3
6.0𝑔−2.0𝑔
= 1.3𝑔/𝑐𝑚3
3.2𝑐𝑚 3
6.0𝑔−2.2𝑔
3.2𝑐𝑚 3
= 1.2𝑔/𝑐𝑚3
Average density for stone at 6.0g =
1.3𝑔/𝑐𝑚 3 +1.3𝑔/𝑐𝑚 3 +1.2𝑔/𝑐𝑚 2
3
=1.3g/𝑐𝑚3
Density of the stone at 26.0g :
First trial :
26.0𝑔−12.0𝑔
13.0𝑐𝑚 3
Second trial :
Third trial :
= 1.1𝑔/𝑐𝑚3
26.0𝑔−12.1𝑔
13.0𝑐𝑚 3
26.0𝑔−12.3𝑔
13.3𝑐𝑚 3
= 1.1𝑔/𝑐𝑚3
= 1.0𝑔/𝑐𝑚3
Average density of stone at 26.0g =
1.1𝑔/𝑐𝑚 3 +1.1𝑔/𝑐𝑚 3 +1.0𝑔/𝑐𝑚 3
= 1.1g/𝑐𝑚3
3
Argument from evidence
After conduct the experiment, we can conclude that all object in this world have their own
volume. The rock volume from the experiment can be calculate by the water that disperse
from the Eureka Can. We agree that Archimedes' principle influenced our experiment because
the principle said that, an object displaces a volume of liquid equal to its own volume.
Obtaining, Evaluating information
Based from the experiment, we not only can get the volume of rocks but also it density.
Density is the mass per unit volume of a substance ρ = M / V. If an object’s density is greater
than 1.0, it will sink in water like the rock. If the object’s density is lower than 1.0, it will float.
The same relationship will be true for other liquids. For example, if you mix vegetable oil and
water, the oil will rise to the top since it’s less dense than water.
Engaging in Argument from Evidence
Before conduct the experiment, we have taken the precaution to prevent dangerous or error in
the experiment. The reason we need to take a precaution is laboratories are dangerous and if
safety precautions are not taken, there is a possibility of mishap. One of the precaution that has
taken is we follow all the rule of the lab. For example, we wear the lab coat and do not wear
slipper in the lab. We also read and understand the procedure so the experiment can be done
without any flaws. Even though we take all this procedure, we still cannot avoid the problem
and error. One of the problem is we use a several rock as our object in this experiment and we
cannot calculate the volume of rock because its irregular shape. We overcome this problem by
using the Archimedes’ Principle because not only it can be used to find the density of object,
it also can be used to find the volume of object. The second problem is there is a probability
that the thread that tie with the rock will soak after use it continuously and can disturb the result
of the displaced water of the object. We solve it by change the new thread after use it for the
first rock and repeat it at the second rock. The error from this experiment is when we read the
volume scale, there is a chance that our measuring is not accurate. We solve this problem by
make a 3 trial for every different shape of rock and take it average. After conduct the
experiment, we can conclude that all object in this world have their own volume. The rock
volume from the experiment can be calculate by the water that disperse from the Eureka Can.
We agree that Archimedes' principle influenced our experiment because the principle said that,
an object displaces a volume of liquid equal to its own volume.
Conclusion
Practically, the Archimedes' principle allows the buoyancy of an object partially or wholly
immersed in a liquid to be calculated. The downward force on the object is simply its weight.
The upward, or buoyant force on the object is that stated by Archimedes' principle. Thus the
net upward force on the object is the difference between the buoyant force and its weight. If
this net force is positive, the object rises, if negative, the object sinks and if zero, the object is
neutrally buoyant - that is, it remains in place without either rising or sinking.
But in relation to the experiment done which explains the main thought of the Archimedes
principle, which tells that it is mainly about the upward force or the buoyant force applied by
the liquid to a certain object being submerged to it. It is the weight of the body in air minus the
weight of the body in liquid is the weight displaced of the liquid, which is the total weight
countered by the liquid. This is explained why objects weigh less in liquid.
In the experiment, the setup was successful in creating a sample situation for the three different
mass of stones that proves the accuracy of the actual values of their specific gravity. Hence,
from the experiment that was done by us, it is clearly shown that when an object is immersed
in water, the buoyant force (upthrust force) on the object is equal to the weight of water
displaced.
References
1) Haileybury Follow. (2016, July 20). Introduction to Buoyancy. Retrieved from
(https://www.slideshare.net/mrsimpson07/introduction-to-buoyancy)
2) Smith, A. (2019, January 10). How to Calculate Buoyant Force. Retrieved from
(https://sciencing.com/calculate-buoyant-force-5149859.html)
3) Physics
of
Ships
at
Sea.
(2014,
January
21).
Retrieved
from
Retrieved
from
(http://passyworldofphysics.com/phyics-of-ships-at-sea/ )
4) LadyNiel, M. (2008, August 30) Retrieved from
(https://maryladyniel.weebly.com/1--submarine.html )
5) Brisbane.
(2009,
September
07).
Flight
Info.
(https://www.brisbanehotairballooning.com.au/how-hot-air-balloons-fly/ )