This is my third
assignment on data logging. We had choosed the title on Buoyant Force.
Below is the
results:
BUOYANT FORCE
INTRODUCTION
Buoyancy is the ability to float. Buoyancy forces are
formed by a principle called Archimedes principle. Archimedes principle said
that buoyancy forces is directly proportional with drowned volume.
Mathematically, Buoyancy force is: F = ρ . g . V, where ρ
is the density of fluid (water), g is gravity, and V is volume which is
drowned.
Any object that is completely or partially submerged in a fluid is
buoyed up by a force equal to the weight of the fluid displaced by the body.
Everyone has experienced Archimedes’s principle. As an example of a common
experience, recall that it is relatively easy to lift someone if the person is
in a swimming pool whereas lifting that same individual on dry land is much harder.
Evidently, water provides partial support to any object placed in it. The
upward force that the fluid exerts on an object submerged in it is called the
buoyant force.
According to the Archimedes’s principle, the magnitude of the buoyant
force always equal to the weight of the fluid displaced by the object. The
buoyant force acts vertically upward through what was the centre of gravity of
the displaced fluid.
F = W
Where F is the
buoyant force and W is the weight of the displaced fluid. The units of the
buoyant force and the weight are Newton (N).
The buoyant force acting on the steel
is the same as the buoyant force acting on a cube of fluid of the same
dimensions. This result applies for a submerged object of any shape, size, or
density.
 |
Figure 1:
Direction of buoyant force
|
The boat can
float on water based on this principle. Boat has hull to get buoyancy force and
makes the boat float. So, it is very important to keep hull safe. In the sea,
corals are sometimes found in the sea. Hull can causes the boat drowned since
hull is the source of buoyancy force.
ENGAGE
 |
Figure 2: Examples of application in buoyant force
- · What is buoyant force?
- · How buoyant force determine whether an object sinks or floats on water?
- · Is there any different if the boat is floating on fresh water and salt water.
- · What factors that influence buoyant force?
- · What principle related to buoyant force?
EMPOWER
Planning and doing an experiment:
Title : The effect of mass of different objects on the buoyant
force.
Objective :
- Use a Force Sensor to measure the weights of objects in and out of water
- Determine the weight of water displaced by each of the objects
- Determine the relationship of depth of the immersed object to the buoyant force.
Hypothesis :
The
magnitude of the buoyant force is directly proportional to the weight of the
fluid that the object displaces.
Procedures :
PART 1
: COMPUTER SETUP
 | ||||||
| Figure 3 : Computer Set
Up
1.
Connect
the Science Workshop interface to the
computer, turn on the interface,
and turn on the computer.
2. Connect
the DIN plug of the Force Sensor to Analog Channel A.
3. Open
the document titled as shown:
·
The DataStudio document has a Workbook
display.
·
The ScienceWorkshop document has a Graph
display with Force versus Depth.
·
Data
recording is set for 1 Hz. Keyboard Sampling allows the user to enter the
submerged depth in meters.
|
PART 2 : SENSOR CALIBRATION AND EQUIPMENT SETUP
Figure 4: Equipment Set Up
- Mount the Force Sensor on a horizontal rod with the hook end down.
- Using the calipers, measure the diameter of the aluminium cylinder. From the diameter, calculate the radius and the cross-section area. Record the cross-section area in the Data Table in the Lab Report section.
- Hang the aluminium cylinder from the Force Sensor hook with a string.
- Put about 800 mL of water into the beaker and place the beaker on the lab jack below the hanging cylinder. The bottom of the cylinder should be touching the water.
- Position the metric ruler next to the edge of the lab jack. Note the initial height of the top of the lab jack.
PART 3 : DATA RECORDING
1. With the cylinder attached to the Force
Sensor hook, press the tare button on the Force Sensor to zero the sensor.
2.
Record Force vs. Depth data as you submerge
the cylinder.
In DataStudio,
move the Table display so you can see it clearly.
• Click
on the ‘Start’ button to start recording data. The ‘Start’ button changes to a
‘Keep’ and a ‘Stop’ button. The Force will appear in the first cell in
the Table display. Click the ‘Keep’ button to record the force value.
• Immerse
the cylinder 1 millimeters (1 mm or 0.001 m) by raising the beaker of water 1
mm with the lab jack. Use the metric ruler to measure the distance that you
raise the lab jack.
• Click
the Keep button to record the next Force value at the depth of 0.001 m.
• Increase
the depth of submersion by increments of 1 mm. After each increase in the
submersion, wait for the force reading in the display to stabilize, then click
the Keep button to record a Force value at the appropriate depth.
• Repeat
the data recording procedure until the top of the cylinder is submerged. Stop
data recording by clicking on the ‘Stop’ button. Run #1 will appear in the
Summary window.
In ScienceWorkshop,
click the ‘REC’ button to begin collecting data.
 |
| Figure 3 : Keyboard Sampling |
• The
‘Keyboard Sampling’ window will open. Move it so you can also see the Digits
display. The default value for ‘Entry #1’ is 10.000.
• Because
the cylinder is not submerged, type in ‘0’ as the depth. Click ‘Enter’ to
record the depth and force values. The entered depth value will appear in the
Data list.
• Immerse
the cylinder 1 millimeters (1 mm or 0.001 m) by raising the beaker of water 1
mm with the lab jack. Use the metric ruler to measure the distance that you
raise the lab jack.
• For
‘Entry #2’, type in ‘0.001’ (1 millimeters). Click ‘Enter’ to record the depth
and force values.
• Increase
the depth of submersion by increments of 1 mm. After each increase in the
submersion, wait for the force reading in the Digits display to stabilize, then
click the Enter button to record a Force value at the appropriate depth.
• Repeat
the data recording procedure until the top of the cylinder is submerged. Stop
data recording by clicking the ‘Stop Sampling’ button in the ‘Keyboard
Sampling’ window.
• The
‘Keyboard Sampling’ window will disappear. ‘Run #1’ will appear in the Data
List in the Experiment Setup window.
PART 4 : REPETITION OF THE PROCEDURE USING
DIFFERENT OBJECTS
•
Repeat
the procedure in part 2 for step 2 with the brass and copper.
Results :
Aluminium
|
Brass
|
Copper
|
|
Actual mass of sample
(g)
|
26.16
|
111.39
|
102.65
|
Diameter of sample (g)
|
1.88
|
1.88
|
1.88
|
Sample height (cm)
|
3.45
|
4.29
|
4.49
|
Density (ρ) H20 (g/cm3)
|
1.00
|
1.00
|
1.00
|
Apparent mass in H20 (g)
|
15.25
|
89.26
|
97.30
|
Calculation :
Aluminium
|
Brass
|
Copper
|
|
Actual weight of sample
(cm/s2)
|
25654.07
|
100664.75
|
109235.72
|
Density of sample (g/cm3)
|
2.78
|
8.78
|
9.13
|
Area of sample (cm2)
|
2.78
|
2.78
|
2.78
|
Volume of cylinder (cm3)
|
9.58
|
11.91
|
12.46
|
Displaced liquid volume= Fb
|
9.43
|
11.70
|
12.20
|
 |
Graph 1 : Force against depth graph
|
Discussion :
In this experiment, we study about the relationship water
displaced and buoyancy force. Archimedes principle says that the buoyant force
on a submerged object is equal to the weight of the fluid it displaces. Thus,
in short, buoyancy = weight of displaced fluid. This principle is useful for
determining the volume and therefore the density of an
irregularly shaped object by measuring its mass in air and its
effective mass when submerged in water (density = 1 gram per cubic centimetre).
This effective mass under water will be its actual mass minus the mass of the
fluid displaced. The difference between the real and effective mass therefore
gives the mass of water displaced and allows the calculation of the volume of
the irregularly shaped object. The mass divided by the volume thus determined
gives a measure of the average density of the object. Buoyancy shows
that the buoyant force on a volume of water and a submerged object of the same
volume is the same. Since it exactly supports the volume of water, it follows
that the buoyant force on any submerged object is equal to the weight of the
water displaced.
Based on the result of the experiment, we can
see that as the mass of the object increase the volume of the fluid displaced
also increase. This means that the
buoyant force is also increase since the formula for the buoyancy is equal to
the weight of displaced fluid.
For the force against depth graph, we can see that force
is directly proportional to the depth.
As the depth of the immersed object increase, the magnitude of the buoyant
force is also increase.
Questions:
1.
Why
was the Force Sensor zeroed after the cylinder was attached to the hook?
The
force sensor measures the net force that is the cylinder’s weight (downward
force) minus the buoyant force (upward force).
By taring the force sensor when the cylinder was attached and out of
water, the weight was accounted for during calibration and the sensor will now
report only the buoyant (upward) force.
2. What is the effects of mass of sample to the buoyant
force?
The mass of sample will affect the magnitude of the
buoyant force since formula
of the density is the mass over volume.
3. In that experiment, what the objects give the lowest and
highest buoyant force?
The object that gives the lowest of buoyant force is the
aluminium whereas the
object that gives the highest of buoyant force is the
copper. This results depend
on the
density of that objects.
Conclusion:
As conclusion, an object that floats displaces the amount
of water that has the same weight as the object. If it sinks, it displaces an
amount of water that has less weight than the object.
ENHANCE
The application
of buoyant force play an important roles
in our daily life. Discuss the important of buoyancy control in diving?
Answer:
Controlling
buoyancy is a key component of your diving safety. The physics of floating and
sinking are simple concepts, yet achieving practical control of your buoyancy
when outfitted with scuba equipment and immersed in water is an entirely other
matter. Each change in equipment affects your buoyancy. As your dive equipment
grows more complex, the more attention your buoyancy requires. Given its role
as a fundamental element of dive safety, it's no wonder problems with buoyancy
control are often the underlying cause of a dive injury or fatality.
Divers with proper buoyancy control can maintain their position with very little effort. They can descend or ascend at will. In contrast, divers with poor buoyancy-control skills struggle throughout the dive. In extreme situations, major buoyancy-control issues may cause divers to make grave errors such as descending well beyond their planned depth, negatively affecting gas consumption and no-decompression calculations, or on the flip side, uncontrolled ascents, increasing the risk of decompression illness. There is no doubt buoyancy control affects many aspects of dive safety. Experts in dive training, dive medicine and research all know just how integral it is and are always eager to share thoughts on how to develop and maintain good skills.
Divers with proper buoyancy control can maintain their position with very little effort. They can descend or ascend at will. In contrast, divers with poor buoyancy-control skills struggle throughout the dive. In extreme situations, major buoyancy-control issues may cause divers to make grave errors such as descending well beyond their planned depth, negatively affecting gas consumption and no-decompression calculations, or on the flip side, uncontrolled ascents, increasing the risk of decompression illness. There is no doubt buoyancy control affects many aspects of dive safety. Experts in dive training, dive medicine and research all know just how integral it is and are always eager to share thoughts on how to develop and maintain good skills.
Training
Good
buoyancy begins with proper weighting. It is imperative the amount of weight
you use allows you to descend, not causes you to do so. Weight
placement makes a difference, too. A classic buoyancy-control device (BCD) is
generally configured to require a separate weight belt, whereas newer BCDs
often integrate the weights. Each approach affects a diver's body position in
the water, requiring time and attention to get comfortable. Using rental gear
can complicate the process, especially for new divers, as each change in
configuration, responsiveness and other variables can alter a diver's comfort
and buoyancy. Diving with a dry suit, a weight harness or a rebreather adds to
the complexity.
The BCD is the most complex piece of scuba
equipment a diver must master. To truly master buoyancy control, a diver must
understand his BCD inside and out, including knowing how it reacts to the
addition or venting of air. It requires proper maintenance (see
"Gear," Alert Diver, Spring 2011) to prevent sticking
buttons or leaking bladders. Malfunctioning BCDs can lead to uncontrolled
ascents or descents before a diver even realizes what's happening. Like any
piece of equipment, proper function requires proper maintenance. But lack of
maintenance is not the only concern; operator error can also cause loss of
control. Improperly connecting a low pressure inflator can cause negative
buoyancy without a means to correct it. Hitting the inflator button instead of
the vent button can cause a rapid ascent. Every diver needs to be familiar with
his own equipment as well as his buddy's. In a stressful or emergency situation
there may not be time to search for weight releases or inflator/deflator
valves.
Figure 5 : Diving Training
Dive Medicine
Many do
not equate buoyancy skills with dive medicine, but there is definitely a
connection. The most common dive injury is consistently middle-ear barotraumas.
There are certainly many factors that lead to this injury, but buoyancy issues
are often among them. Every diver is taught that if discomfort is felt during
descent to stop the descent, ascend a few feet or until the discomfort
resolves, and then attempt to equalize again. This is very difficult to execute
without good buoyancy control. When experiencing a reverse block during ascent,
a diver should stop the ascent, descend until the discomfort resolves and
attempt ascent again using appropriate equalization manoeuvres. The ability to
stabilize and adjust position in the water column certainly takes practice, but
as a cornerstone skill, it's worth the effort.
Most marine life injuries are due to incidental contact. Proper buoyancy helps divers avoid contact as it maintains necessary distance from marine life. It also prevents the destruction of the reef and the microscopic critters that live on sub aquatic surfaces, as buoyancy control reduces the need to place hands on those surfaces to steady a diver's position. Buoyancy skills not only protect divers but the environment as well.
Most marine life injuries are due to incidental contact. Proper buoyancy helps divers avoid contact as it maintains necessary distance from marine life. It also prevents the destruction of the reef and the microscopic critters that live on sub aquatic surfaces, as buoyancy control reduces the need to place hands on those surfaces to steady a diver's position. Buoyancy skills not only protect divers but the environment as well.
Finally, one of the most serious consequences of
inadequate buoyancy control is a rapid ascent. This can place a diver at risk
for a lung overexpansion injury (pulmonary barotraumas), and it also increases
the risk of a potentially fatal arterial gas embolism (AGE). The easiest way to
avoid both these injuries is to learn the best method of prevention good
buoyancy.
 |
| Figure 6 : Barotraumas Ear |
EXTENSION
 |
Figure 7 :
Application of buoyant force
The application
of buoyancy can be applied to staying
afloat on the water. In the early 1800s, a young Missippi River flat-boat
operator submitted a patent application describing a device for “buoying
vessels over shoals”. The invention proposed to prevent a problem he had often
witnessed on the river-boats ground on sandbars-by equipping the boats with
adjustable buoyant air chambers. The young man even whittles a model of his
invention, but he was not destined for fame as an inventor; instead Abraham Lincoln
(1809-1865) was famous for much else. In fact Lincoln had a sound idea with his proposal to use buoyant
force in protecting boats from running aground.
|
Buoyancy on the surface of water has a
number of easily noticeable effects in the real world. (Having established the
definition of fluid, from this point onward, the fluids discussed will be
primarily those most commonly experienced: water and air). It is due to
buoyancy that fish, human swimmers, icebergs, and ships stay afloat. Fish offer
an interesting application of volume change as a means of altering buoyancy: a
fish has an interesting swim bladder, which is filled with gas. When it needs
to rise or descend, it changes the volume in its swim bladder, which then
changes its density. The examples of swimmers and icebergs directly illustrate
the principle of density- on the part of the water in the first instance, and
on the part of the object itself in the second.
To a swimmer, the difference between
swimming in fresh water and salt water shows that buoyant force depends as much
on the density of the fluids as on the volume displaced. Fresh water has a
density of 62.4lb/ft3 (9,925N/m3), whereas that of salt
water is 64lb/ft3 (10,167N/m3). For this reason, salt
water provides more buoyant force than fresh water; in Israel’s Dead Sea, the
saltiest body of water on Earth, bathers experience an enormous amount of
buoyant force.
Water is an unusual substance in a
number of regards, not least its behaviour as it freezes. Close to the freezing
point, water thicken up, but once it turns to ice, it becomes less dense. This
is why ice cubes and icebergs float. However, their low density in comparison
to the water around them means that only part of an icebergs stay atop the
surface. The submerged percentage of an iceberg is the same as the ratio of the
density of ice to that of water: 89%.
UNIQUE FEATURE
OF THIS EXPERIMENT
·
Buoyancy
is defined as the tendency of a fluid to exert a supporting upward
force on a
body placed in the fluid.
·
Buoyant
force must equal to the weight of the displaced fluid.
· A
solid object would float if the density of the solid object were less than the density of the fluid and vice versa.
REFERENCES:
Air Consumption (2012).
Retrieved on November 17, 2012 from http://www.saireecottagediving.com/air-consumption/
Buoyant Forces and Archimedes' Principle (2006). Retrieved on November 15,
2012 from http://www.engineering.com/Library/ArticlesPage/tabid/85/ArticleID/205/Buoyant-Forces-and-Archimedes-Principle.aspx
Buoyancy Force application (2011). Retrieved on November 16,
2012 from http://simple-engineering.blogspot.com/2011/08/buoyancy-force-application.html
Experiment P18: Buoyant Force (Force Sensor)
(1996).
Retrieved on November 14, 2012 from http://kcyap.home.nie.edu.sg/qcp521/Updated_Experiment1_Buoyant_Force.pdf
J. Andrew Doyle
(1999). Swimming. Retrieved on November 15, 2012 from http://www2.gsu.edu/~wwwfit/swimming.html
The
importance of buoyancy-driven water flow in Sphagnum dominated peat bogs
(2011). Retrieved on November 18, 2012 from http://www.rug.nl/biologie/onderzoek/onderzoekgroepen/plantfysiologie/organisatie/patbergresearch
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