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I need help on the labsName
Date
Class
Lab 20: Density and Buoyancy
Problem
To learn how to predict whether an object will ﬂoat or sink
Background
Eureka! According to popular legend, in the 3rd century B.C. the Greek
mathematician Archimedes discovered that there was a relationship between
the amount of water he displaced when getting in a bathtub and the buoyant
force that made him feel lighter in the water. This discovery lead to the
principle named after him, which states that “an immersed object is buoyed up
by a force equal to the weight of the ﬂuid it displaces.”
Why do some objects ﬂoat and others sink? The answer depends partly on the
densities of the object itself and the liquid it is placed in. Density is the mass of
a material in one unit of volume. The mathematical formula for density is given
below.
Density = Mass
or d = m
Volume
V
—————–The answer also depends on the volume
of ﬂuid that is displaced by the object.
The shape of an object affects how much ﬂuid is displaced–which explains why
a solid block of iron will sink, while the same mass of iron when shaped in the
form of a boat would ﬂoat.
Skills Focus
Problem solving, calculating, applying concepts, predicting, drawing conclusions
Procedure
Density of a Solid
1. Start Virtual Physics and select Density and Buoyancy from the list of
assignments. The lab will open in the Density laboratory.
2. You will be measuring the density of solid objects and of various liquids to
predict whether the solids will ﬂoat or sink. You will also calculate the
buoyant force on the solids in one of the ﬂuids. Find the ice ball on the lab
wall. Pick up the ball and drag it to the spotlight on the balance. Record its
mass in Data Table 1.
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Density and Buoyancy
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3. Use the Up and Down arrows on the control panel to toggle through the
options of ﬂuids to use in the lab. Select Virtual Fluid B. This is a unique
Virtual Fluid that is used only in this virtual laboratory. Click the Full button
underneath that display to select the amount of ﬂuid to be added to the
cylinder. Click the Fill button to release the chosen amount of ﬂuid into the
250 mL graduated cylinder on the laboratory bench. Click on the top of the
cylinder to see a zoomed in view of the level of the ﬂuid. Record the volume
of the Virtual Fluid in Data Table 1.
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Class
4. Drag the ice ball to the top of the cylinder and drop it in the cylinder of
Virtual Fluid. Click the green Drop button to let the ball fall into the ﬂuid.
Look at the close-up view window to note the new volume of the cylinder
with both the Virtual Fluid and the ball. Record the volume in the table.
5. Problem Solving How can you determine the volume of the ice ball from
Record the volume of the ice sample in Data Table 1. Click the handle at the
bottom of the cylinder to empty the contents of the cylinder.
6. Repeat Steps 2–5 for two more samples: aluminum and pine wood. Record
your measurements in Data Table 1.
7. Calculate the weight of each of the objects. Remember Weight
force of gravity (g). Use the mass of the objects in kg and use g
mass
9.8 m/s2.
Data Table 1
Sample
Mass
of
Sample
(g)
Volume
of
Virtual
Fluid
(mL)
Volume
of Virtual
Fluid and
Sample
(mL)
Volume
of
Sample
(mL)
Weight
of solid
(N)
Density
(g/mL)
Buoyant
force in
olive oil
(N)
Ice
Aluminum
Pine Wood
Density of a Liquid
8. Use the Up and Down arrows on the control panel to toggle through the
options of ﬂuids to use in the lab. Select Ethanol. Click the Full button
underneath that display to select the amount of ﬂuid to be added to the
cylinder. Click the Fill button to release the chosen amount of ﬂuid into the
cylinder. Click on the cylinder to see a zoomed in view of the level of the
ﬂuid. Record the volume in Data Table 2.
9. Drag the empty beaker on the counter to the balance and record its mass in
Data Table 2.
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10. Pick up the cylinder ﬁlled with ethanol and pour it into the empty beaker.
Record the mass of the ethanol and beaker in Data Table 2.
Density and Buoyancy
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11. Problem Solving
beaker?
Class
How can you determine the mass of the ethanol in the
Record the mass of the ethanol in Data Table 2. Click the handle at the
bottom of the cylinder to empty the contents of the cylinder.
12. Repeat Steps 8–11 to obtain the densities of water and olive oil. Record
your measurements in Data Table 2.
Data Table 2
Sample
Volume of
Sample (mL)
Mass of
Empty
Beaker (g)
Mass of
Beaker and
Sample (g)
Mass of
Sample (g)
Density
(g/mL)
Ethanol
Water
Olive oil
Analyze and Conclude
1. Calculating Use the formula for density to calculate the density of each of
2. Calculating Use the same formula as above to calculate the density of each
of the liquid samples. Record the answers in Data Table 2.
3. Applying Concepts Does the weight of an object or its density determine
whether or not it will ﬂoat in a ﬂuid? Explain.
Density and Buoyancy
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4. Predicting Which of the solids will ﬂoat in the olive oil? Explain.
Calculate the buoyant force on each of the objects in the olive oil. You have
calculated the volume of ﬂuid displaced by each of the objects and the
density of the olive oil. Use the density equation to calculate the mass of
olive oil displaced, from the density and volume that you have. To calculate
the buoyant force, you need to calculate the weight of the displaced olive oil
in each case.
Buoyant force on object = Weight of displaced ﬂuid =
Mass of displaced ﬂuid X g
Record your results in Data Table 1. You can tell if each object will sink or
ﬂoat by comparing the weight of the object and the buoyant force. If the
buoyant force is larger, the object has more force pushing up than the weight
of the object pulling it down, so it will ﬂoat. Compare the two forces to
predict which objects will ﬂoat.
5. Test your prediction by ﬁlling the cylinder with olive oil. Then move the
dispenser head over the next cylinder by clicking it and dragging it until it
clicks in place above the cylinder. Fill three cylinders with olive oil. Place
each of the objects in one of the cylinders and release them all to see whether
or not they will ﬂoat.
6. Predicting What would you observe if olive oil and water were poured
together?
Test your prediction by half ﬁlling one of the cylinders with olive oil by
clicking the –1 button on the dispenser control before ﬁlling. That will allow
2
you to add half a cylinder of oil, then toggle through the ﬂuids and select
water and dispense –1 of a ﬁll of water to the same cylinder.
2
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7. Drawing Conclusions If all three solids and all three liquids were mixed
in the same cylinder at the same time, what would you observe? List the
solids and liquids that you would see from the top of the cylinder to the
bottom. Explain how you determined your placement.
Density and Buoyancy
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Name
Date
Class
Lab 21: Pressure and Volume of a Gas
Purpose
To discover how changing the pressure on a gas-ﬁlled balloon affects the
volume of the balloon
Background
Robert Boyle, a philosopher and theologian, studied the properties of gases in
the 17th century. He noticed that gases behave like springs. When compressed
or expanded, gases tend to ‘spring’ back to their original volume. Boyle studied
the relationship between the pressure and volume of a gas and summarized his
results in what has become known as Boyle’s Law. You can make observations
similar to those of Robert Boyle by changing the pressure of a gas and
observing what happens to its volume.
Skills Focus
Graphing, drawing conclusions, interpreting data, predicting
Procedure
1. Start Virtual Physics and select Pressure and Volume of a Gas from the list of
assignments. The lab will open in the Gases laboratory. Note that the balloon
in the chamber is ﬁlled with a gas at a temperature of 25C. The pressure of
the gas is 100 kPa. The volume of the balloon is 7,436 cm 3.
2. Predicting You are going to increase the pressure on the balloon. What do
you think will happen to the volume of the balloon? Record your prediction.
3. Observe the beginning pressure and volume of the gas and record them in
the table. Now, click on the 1 in the pressure window. The digit should turn
green. Type 2 so that the pressure becomes 200 kPa. Record the new pressure
and volume in the table. Repeat this step again but set the pressure to
300 kPa. Again, record your data. Continue to increase the pressure by
100 kPa each time and record your data until you reach 700 kPa.
Pressure (kPa)
Pressure and Volume of a Gas
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Volume (cm3)
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Date
Class
Analyze and Conclude
D 1. Graphing
Make a line graph of the data in the table. Show Pressure in
kPa on the horizontal axis and Volume in cm3 on the vertical axis.
3. Interpreting Data
or nonlinear?
Is the relationship between pressure and volume linear
4. Predicting How would the volume of the gas be affected if the pressure
were decreased?
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Decrease the pressure on the balloon to check your prediction. Pull down on
the lever on the pressure controller until the tens digit turns blue and hold it.
This causes the pressure to decrease. Observe the balloon volume as the
pressure decreases. What relationship do you observe?
Pressure and Volume of a Gas
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Name
Date
Class
Lab 23: Phase Changes
Purpose
To study the phase changes as water is heated from solid to liquid to water
vapor
Background
Depending on the temperature, most substances can exist as either a solid or a
liquid. A substance in its liquid state has more thermal energy than it has in its
solid state. The temperature at which the transition from a solid to a liquid
takes place is called the melting point of the substance.
The molecules that make up a gas have more thermal energy than do molecules
of the same substance in the liquid state. The liquid’s molecules are in close
contact with each other while gas particles are spaced signiﬁcantly further
apart. The transition from a liquid to a gas is known as vaporization and occurs
by either evaporation or boiling. The normal boiling point is the temperature at
which the substance boils at sea level. Melting and vaporization points are
characteristic properties of a substance. Chemists often use these points to help
identify or classify a substance.
Skills Focus
Graphing, interpreting data, applying concepts, drawing conclusions, relating
cause and effect, making judgments
Procedure
1. Start Virtual Physics and select Phase Changes from the list of assignments.
The lab will open in the Calorimetry laboratory.
2. The experiment will be set up with a coffee cup calorimeter ﬁlled with
65 mL of room temperature water on the lab bench. There is a beaker on the
table next to the balance. Click on the balance area and then drag the beaker
to the balance and click on the Tare button to zero out the balance. Drag the
beaker back to the spotlight on the table and click Zoom Out. Click on the
green ice bucket and drag the scoop down to ﬁll it. Drag the scoop of ice
over to the beaker until it snaps into place and then release the ice into the
beaker. Click the Save button in the Thermometer window to begin saving
the temperature data. Click on the balance to zoom down and drag the
beaker to the balance. Record the mass of ice on the line below. You will
observe the temperature change as the ice chills the water and then as the ice
melts due to stirring and being out at room temperature.
Phase Changes
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Class
3. Zoom Out again and carry the beaker over to the calorimeter to release the
ice into the cup. Click the clock on the wall labeled Accelerate to accelerate
the laboratory time. Click on the Lab Book to open it, and click the Plot
window to bring it to the front.
4. Observe the temperature of the ice/water mixture graphed in the plot
window as a function of time until the temperature starts to rise as the water
heats up to room temperature, after about 4 minutes.
5. You will now heat up the water and observe the temperature change as the
water turns into steam. Turn on the heater by clicking on the green light on
the control panel labeled Heat. Observe the temperature of the water
graphed in the Plot window as a function of time until steam begins to form
above the coffee cup calorimeter. Record the temperature at which boiling
begins in the data table. Continue to observe the graph until two more
minutes have passed. (Use the graph to know when 2 minutes have passed.)
Click Stop in the Thermometer window.
6. Click on the barometer to the left of the green Exit sign to display the
pressure in the virtual laboratory. Record this pressure in the data table. The
pressure is displayed on this meter only in torr. A torr is another unit of
pressure commonly used by scientists. There are 760 torr in 101.3 kPa.
Data Table
Temperature at Boiling
Pressure at Boiling
7. A blue link will appear in the lab book after you have stopped the
thermometer. Click on the data link to display the temperature data.
Analyze and Conclude
ISBN 0-558-83901-0
1. Graphing In the graph grid on the following page, graph the temperature
of the water as a function of time. Use the data from the data link. You do
not need to plot every point—just plot enough points to show all of the
critical sections of the graph. Label the axes and label where on the line the
ice was added, the mixture is a combination of liquid water and solid ice,
and the mixture is all liquid water. Also label where the heater was turned
on and where the water is changing to a gas. Remember to scale the axes
appropriately.
Phase Changes
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Class
2. Interpreting Graphs What phase or phases are in the calorimeter at 0C?
3. Applying Concepts What happens to the temperature while there is still
ice in the water? Why?
4. Drawing Conclusions
ice has melted? Why?
What happens to the temperature after all of the
5. Applying Concepts What happens to the temperature of the water as the
heater continues to heat after the water has come to a boil? Why?
Phase Changes
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Class
6. Relating Cause and Effect The average or typical air pressure at sea level
is 760 torr. This pressure may vary by about ±15 torr depending on the
weather. In stormy weather, the pressure drops lower. Good weather
brings higher pressure. The normal boiling point of water at sea level
pressure is 100C. From your observation of the boiling point and air
pressure what can you conclude?
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7. Making Judgments
Which phase change required more energy? Explain.
Phase Changes
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