Chapter 3: Fluids and Pressure
Imagine the following situation:
One afternoon, you go outside to find your younger sister standing by
her bike with a nail in her hand. The bike has a flat tire. She wants to
know why the air came out of the tire when she pulled the nail out.
Write a few sentences to explain why air rushes out of a hole in a tire.
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The Rise and Fall of Raisins
Purpose: To observe the effects of alka seltzer on raisins and describe results in terms of relative density.
Hypothesis:
What do you think will happen when the raisins are placed in the water with the alka seltzer?
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Procedure:
Fill a beaker with water.
Drop a seltzer tablet into the water.
The drop 5 raisins in the water.
Write down observations below.
Observations:
What happens when the alka seltzer and the raisins are put into the water?
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Hypothesis:
What do you think will happen when the raisins are placed in the water without the alka seltzer?
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Procedure:
Fill a beaker with water.
The drop 5 raisins in the water.
Write down observations below.
Observations:
What happens when the raisins are put into the water?
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Discussion:
What was the purpose of the alka seltzer?
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Water is denser than Carbon Dioxide ( CO2 ) but less dense than a raisin. How can this statement be used to explain the behavior of raisins?
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What is the difference between a liquid and a solid?
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______and ______are referred to as fluids.
Define a fluid ( page 66)
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There is 100 mL of water in the graduated cylinder. How many mL of water will there be in the beaker? The flask?
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What does it mean for a fluid to flow?
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Why can a solid not be considered a fluid?
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Explain how fluids create pressure. ( page 66)
(HINT: use Newton's laws and forces)
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Who was Blaise Pascal?
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Calculating Pressure
Pressure =
The SI unit for pressure is the ______
Force is measured in ______
Area is measured in______
What is the pressure of a hose that shoots water out of it at a force of
1 034 213 N in an area of 1 m2?
1) Find the pressure exerted by a 3000 N crate that has an area of 2 m2.
2) Find the weight of a rock that has an area of 10 m2 exerts a pressure of 250 Pa.
Which exerts more pressure? Why?
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Atmospheric Pressure
What is an atmosphere and why do we have one?
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What is air pressure?
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At sea level the pressure of the atmosphere measures:
______atmosphere or
______Torr or
______kilopascals
There is roughly ______of pressure on every ______of your body. The fluids inside your body exert a pressure back on the atmosphere so you do not feel the pressure.
Variation of Atmospheric Pressure
The higher up in the atmosphere you go the less air molecules there are.
What does this do to atmospheric pressure?
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Pressure changes and your body
The fluids in your body need to adjust in order to maintain equal pressure.
Why do your ears “pop” as you ascend in the atmosphere?
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What are some side effects of this “popping?”
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How do you correct the problem?
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Water Pressure
What do you think is going to happen to the pressure on your body as you swim down deeper into water? Why?
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Water is roughly ______times more dense than air.
The pressure increase by ______atmosphere every 33 ft.
Pressure differences and fluid flow
Fluids flow from areas of high pressure to areas of low pressure.