Mini LAB ARCHIMEDES' PRINCIPLE
PURPOSE - FILL THE BLANKS
words bank : apparent - displaced - weight - density of water - buoyed
Archimedes'principle states that an object floating or submerged in a liquid is _________ by a force equal to the _________
of the liquid displaced by the object. The purpose of this experiment is to study this principle as it applies to floating and submerged objects.
The buoyant force of an object immersed in a liquid can be determined by weighing an object in air and then in water.
The apparent loss of weight in water, is the buoyant force. weight in air - weight in liquid = buoyant force.
REmember, the weight in water is called the _________ weight.
There is another way to find the buoyant force. According to Archimedes'principle:
buoyant force = weight of water ___________.
The purpose of this lab is to verify the principle. To find the weight of the water displaced, we will find the volume of the water displaced by using an overflow bucket and catch bucket. We will then use the formula: weight of water displaced = _________ x volume of water displaced x g
The diagram shows that when the object is placed in the bucket, water overflows.
This overflow is the volume of the object. Also the scale shows that the apparent weight
of the object in water is smaller than the true weight. (in air)
weight in air - weight in water = buoyant force
Also the weight of the water displaced = buoyant force.
You have 2 ways to compute this buoyant force.
Also remember
(weight of water displaced = density of water x volume of water displaced x g)
with g = 10m/s/s
PROCEDURE
You will need an object that sinks , one that floats, catch bucket, overflow can
PART 1: A sinking object
step 1: Use a plate scale to find the mass of the empty catch bucket (in grams). m = __________g
convert in kg m = ___________kg. (divide by 1000) then multiply by g = 9.8m/s/s to find the weight. W = _______ N
Fill the information in TABLE 1.
step2: Weigh the object in air. Use a spring scale, BUT USE THE NEWTONS SCALE. weightobject = _________ N
Record the weigh in the TABLE 1. Units are newtons.
step3: Fill an overflow can with water while holding a finger over the spout hole. Place the can on the table, with the spout hole over a catch bucket/ Remove your finger from the spout hole, catching the excess water. When the water in the can is level with the spout , disregard the excess water from the catch bucket and dru it with paper towels. Place the dry catch beneath the spout hole again/
step4: hang the object on the spring scale and slowly immerse it in the can. Record the apparent weigh of the object in the TABLE. While the object was immersed, the overflow water is collected in the bucket.
weight of displaced water = buoyant forcesource image: http://sol.sci.uop.edu/~jfalward/physics17/chapter5/chapter5.html
step5: carefully weigh the catch bucket with the overflow water (grams) with a pan balance. don't spill.
convert to kg. Find the weight by multiplying by g =9.8m/s/s. Record in the TABLE 1
step6: Find the weight of displaced water = weight of full bucket (col 8) - weight of empty bucket (col3). Record in TABLE1
step7: Find the buoyant force by subtracting the apparent weight (col 5) from the weight in air (col4). Record in TABLE 1.
you should get about the same number for step6 and step7/ See image below.
weight in air (3N below ) = weight in water (1 N) + buoyant force (2N)
or boyant force (2N) = weight in air (3N) - weight in water (1N)
and buoyant force (2N) = weight of water displaced.
TABLE 1
| mass (g) empty bucket | mass (kg) empty bucket | weight (N) empty bucket | weight (N) object in air | weight (N) object in water = apparent weight | mass (g) full bucket | mass (kg) full bucket | weight (N) full bucket | weight of displaced water | buoyant force (N) |
| = | = | = | = | = | = | = | = | = | = |
ANALYSIS PART 1
1) Compare the weight of displaced water (col 9) to the buoyant force (weight in air - weight in water). Was Archimedes right ?
(the buoyant force = weight of water displaced)
2) Compare the buoyant force (upward force) to the weight of the object (in air = downward force).
(if the weight is larger, the object sinks)
PART 2: A floating object
When an object floats, the buoyant force balances the weight of the object (in air).
weight of object = buoyant force or upward force = down ward force.
step 1: Use a plate scale to find the mass of the empty catch bucket (in grams) m = _______g.
convert in kg . (divide by 1000) m = ___________kg/ then multiply by g = 9.8m/s/s to find the weight. W = _________N
Fill the information in TABLE 2. (or you can just copy what you got in PART 1)
step2: Weigh the object in air with a spring scale. Use the Newtons scale. . Record the weigh in the TABLE 2. Units are newtons.
step3: Fill an overflow can with water while holding a finger over the spout hole. Place the can on the table, with the spout hole over a catch bucket/ Remove your finger from the spout hole, catching the excess water. When the water in the can is level with the spout , disregard the excess water from the catch bucket and dry it with paper towels.
Place the dry catch beneath the spout hole again/
step4: hang the object on the spring scale and slowly immerse it in the can. holed the spring scale but don't pull on it.
Record the apparent weigh of the object in the TABLE 2. While the object was immersed, the overflow water is collected in the bucket.
(if you get 0, it is ok. why ?)
weight of object = buoyant force, apparent weight = 0, the object floats.step5: carefully weigh the catch bucket with the overflow water (grams) on a pan balance. m = _______g don't spill.
convert to kg. m= ________kg. Find the weight by multiplying by g =9.8m/s/s. W = ________N .Record in the TABLE 2
step6: Find the weight of displaced water = (weight of full bucket (col 8) - weight of empty bucket (col3)) THat is subtract !. Record in TABLE2
step7: Find the buoyant force by subtracting the apparent weight (col 5) from the weight in air (col4). Record in TABLE 2.
you should get about the same number since buoyant force = weight of water displaced = weight in air - weight in water.
TABLE 2
| mass (g) empty bucket | mass (kg) empty bucket | weight (N) empty bucket | weight (N) object in air | weight (N) object in water = apparent weight | mass (g) full bucket | mass (kg) full bucket | weight (N) full bucket | weight of displaced water | buoyant force (N) |
| = | = | = | = | = | = | = | = | = | = |
ANALYSIS PART 2
1) Compare the weight of displaced water (col 9) to the buoyant force. Was Archimedes right ?
(the buoyant force = weight of water displaced = weight of the object in this case)
2) Compare the buoyant force (upward force) to the weight of the object (in air = downward force).
3) Was the purpose of this lab accomplished ? What did you learn ?
GOING FURTHER try without hints
1) A steel box measuring 40cm long, 22cm high, and 35cm wide is submerged in water.
How large is the force exerted on it by the water ? density = 1000 kg/m3 .
a steel box sinks so volume object = volume water displaced.
hint: The buoyant force is the weight of the water displaced.
weight of water displaced = mass of water displaced x g = density of water x volume of water displaced x g
weight of water displaced = density of water x volume of object x g (it sinks)
To compute the volume of the object, convert cm to meters first. V = h x W x L.
2) A rock with a mass of 22 kg, and a volume of 0.018m3 is attached to a spring scale, calibrated in newtons, an immersed in water. What does the spring scale reads? (find the apparent weight = true weight - buoyant force)
hint: Find the weight or true weight of the rock. weight = mass x g.
find the buoyant force = density of water x volume water displaced x g
volume of water displaced = volume of rock (it sinks)/
apparent weight = true weight - buoyant force
3) geologists use the Archimedes to find density of rocks. the just need a spring scale (grams) and a bucket, and the rock
Leave the masses in grams and the volumes in cm3. Use density of water = 1g/cm3.
Use : weight (air) - apparent weight (water) = buoyant force
that is weight in air - apparent weight in water = (mass of water displaced) x g
or mass in air (grams) - apparent mass in water (grams) = mass of water displaced
or mass in air (grams) - apparent mass in water (grams) = volume water displaced x density water
Since the density of water = 1g/cm3, If we know the mass of the rock in air and in the water we can find its volume.
volume of the rock = volume of the water displaced. If we know the volume we can know the density of the rock and
find our what it is made of.
A rock is suspended from a gram-calibrated spring scale, which reads 155g when the rock is in air and 83 g when it is in water.
A) Find the difference between the mass in air and the mass in water.
B) find the volume of water displaced. V = ______ cm3 (use density = 1g/cm3)
(hint: Use the formula highlighted in green )
C) Find the the volume of the rock.
(hint: Use the formula highlighted in yellow)
D) Find the density of rock in g/cm3.
(hint: density = mass (g) / volume (cm3) , use the mass in air )
E)SO for short:
DENSITY OF ROCK = MASS IN AIR (g) / ( MASS IN AIR - MASS IN WATER)
did you get that ?
F) The following table show densities of different rock. (If you take Geology, you might already be familiar with it).
What kind of rock do you think the geologist found ? (SOURCE of the table)
G) See me (at my desk) and I will give rocks. Pretend you are a geologist and try to find its density.
Use the formula given in E) Find, using a spring scale, its mass in air and its mass in water.
mass in air ___________, mass in water __________. Using E), find its density. density = _________ g/ml
Use the table to find the type of rock. rock is _______________________.
4) To find the density of a rock, a geologist suspends it from a spring scale calibrated in mass units - grams.
The scale reads 45g when the rock is in air, and 32 g , when it is in water.
A)What is the density of the rock ?
hint: Follow the same steps as the previous problem
B) What kind of rock is that ?