Pressure and flow

In this virtual laboratory you will investigate properties of fluid pressure and flow.
Link to the simulation:   http://phet.colorado.edu/en/simulation/fluid-pressure-and-flow

The interface

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Try all the different tabs at the top of the simulation. 

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"Reset All" resets only the tab that you are presently using.

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You can use multiple tools to make measurements.

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Sensors are very sensitive, so you may expect some variations in the readings.

Pressure tab

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The "Pressure" tab shows an underground basin containing fluid.  The top of the basin is at sea level.

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The "Grid" option makes it easier to estimate the height of the fluid.

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The "Gravity" slider has few tick marks.  Exact values between 1.0 and 20.0 can be typed in the white text box.

Flow tab

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The handles on the "Flow" tab let you change the shape/height of the water tube and end pipes.

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You can pause the simulation and then use increment time in discreet steps.

Water Tower tab

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Water is allowed to flow out of a hole at the bottom of a tall water tower. 

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The hose on the "Water Tower" tab has 2 controls.  The handle moves the hose vertically and the gold knob rotates the nozzle.

Explorations

To convince me that you did explore the simulation, submit your answers to Question 1 - 5 on Blackboard.

Click the Pressure tab.  Notice what happens under the following conditions.

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As the pressure sensor is moved deeper into the liquid, how does the pressure change?

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As liquid is added or removed from the basin, how does the pressure near the bottom of the tank change?

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How does the pressure in the water change when the atmosphere is removed?

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Keeping all other conditions the same, does the pressure a given distance below the surface depend on the shape of the basin?

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How is the density of the fluid related to the pressure it exerts?

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How does increasing gravity change the pressure in the fluid?

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When g = 9.8 m/s2, how does pressure (in Pa) change for each meter of water depth?

Question 1:

Reset all.  Make sure there is atmosphere above the basin.  The atmosphere is also a fluid, and its density is roughly constant within a few meters of the ground.  Use the ruler and two pressure sensors to measure the change in pressure (in Pa) over a vertical distance of 2 m.  Then use Pbottom - Ptop = ρhg to find the density of the atmosphere in kg/m3What is the density ρ of this atmosphere?

Question 2:

Reset all.  Make sure there is atmosphere above the basin.  Change the fluid density by sliding the density slider all the way to the right to honey.  Fill the basin with honey until the pressure at the bottom is 130 kPa.  What is the height h of the honey in the basin in m?

Click the Flow tab.  Notice what happens under the following conditions.

Reset all.  Choose no friction:

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For a given flow rate, how does the speed change as the pipe diameter changes?

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For a given flow rate, how does the pressure at the bottom of the pipe change as the pipe diameter changes?

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For a given flow rates and pipe diameter, how does the pressure change as the fluid density changes?

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Click the red button to get a representation of the profile of the flow.  Observe it for a straight pipe with constant diameter and for a pipe with varying diameter.

Question 3:

Reset all.  Move the yellow handles in the middle of the pipe to their extreme up and down positions, while leaving everything else untouched.  Measure the pressure as close to the lower wall as possible at two different locations in the pipe near the handles pointed to by arrows in the figure above.  What is the pressure difference in kPa?

Reset all.  Turn on friction:

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For a given flow rate, how does the speed change as the pipe diameter changes?

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Click the red button to get a representation of the profile of the flow.  Observe it for a straight pipe with constant diameter and for a pipe with varying diameter.  Measure the pressure

Question 4:

Reset all.  Turn on friction.  Adjust the flow rate so that the speed as close to the wall of the straight pipe as you can measure is 0.6 m/s.  What is the speed of the liquid in the middle of the pipe in m/s?

Click the Water Tower tab.  Notice what happens under the following conditions.

Open the hole in the bottom of the tank.  Match the leakage to keep water level in the tank constant.  Measure the speed of the fluid just as its exits the tank.

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Does the speed of the flow of the water depend upon the height of the tank?

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Does the speed of the flow depend upon the fluid density?

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What happens to the stream of fluid after it leaves the tank?

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Attach the hose and aim it directly upward.  What do you notice about the height of the fountain created as you use the yellow handles to adjust the height of the tank and the hose.

Question 5:

Reset all.  How far (horizontally) will a stream of water travel if it exits the water tower at 14 m/s 10 m above the ground?
(Click "Match Release", open the hole in the bottom of the tank, and then click "Fill".  Use the yellow handle to move the tank vertically.)

To earn extra credit go to Blackboard, Assignments, and complete the extra credit assignment 1.  You can submit twice.  The highest score counts.