Pressure

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 **__Table of contents:__** 1. Key Terms 2. What is Pressure? 3. Balanced Pressure 4. Fluid Pressure 5. Air Pressure 6. Measuring Pressure ​
 * __Key Terms: __**

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The word pressure is related to the word //press.// It refers to a force pushing on a surface. For example, when you lean against a wall, you push against the wall and so exert pressure on it. When you stand on the ground, the force of gravity pulls you downward. So the soles of your shoes push down on the ground and exert pressure on it (Jones74).
 * __What is Pressure? __ **

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**__ Balanced Pressure __: ** If you hold out your hand then you are holding up air. How could you possibly hold up air? Well in stationary fluids the force exerted by the fluid is equal in both ways. This is called balanced pressure. Balanced pressure can explain why the tremendous air pressure pushing on you from all side does not crush you. Your body contains fluids that exert outward pressure. For example, your lungs and sinus cavities contain air. Your cells and blood vessels contain liquid. So pressure from fluids inside your body balance out the air outside your body(Jones77).

__** Fluid Pressure: **__ Solids such as sneakers are not the only materials that exert pressure. Fluids can also exert pressure. What is a Fluid? Well a Fluid  is a material that can easily flow. As a result, a fluid can change shape. Some examples of a fluid are water, oil and gases such as air and helium(Jones75).


 * __Air Pressure: __**

Air is made up of molecules that are constantly in motion. As air warms up, the molecules start to vibrate and bump into each other, increasing the space around each molecule. Because each molecule uses more space for motion, the air expands and becomes less dense (lighter). In other words, the same number of air molecules occupy a larger space or the same sized space with increased air pressure.
 * [[image:http://www.sciencekidsathome.com/images/hot_air.gif width="166" height="196" align="left" caption="hot air molecules"]] ||

The opposite effect happens when air cools. As the temperature drops, molecules move more slowly, taking up less room. The amount of space the air takes up shrinks, or reduces the air pressure. **<span style="color: #6b2394; font-family: Comic Sans MS,cursive; font-size: 13pt;">__ Measuring __ ****<span style="color: #6b2394; font-family: Comic Sans MS,cursive; font-size: 13pt;">__ Pressure: __ **<span style="color: #6b2394; font-family: Comic Sans MS,cursive; font-size: 13pt;"> //Wikipedia//. Web. 13 May 2010. <http://en.wikipedia.org/wiki/Pressure>. <span style="font-family: Comic Sans MS,cursive; font-size: 13pt;">The SI unit of pressure is the Pascal. One pascal equals the force of one newton exerted over an area of one square meter (1 N/m^2).
 * [[image:http://www.sciencekidsathome.com/images/cold_air.gif width="119" height="149" align="left" caption="cold air molecules "]] ||

<span style="font-family: Comic Sans MS,cursive;"> MATH FOCUS : Pressure, Force, and Area. What is the pressure exerted by a book that has an area of 0.2m^2 and a weight of 10 N? Step 1: Write the equation for pressure. Pressure= Force divided by area. Or as I will show P= F/A Step 2. Replace force and area with the values given, and solve. (Hint: Weight is a measure of gravitational force.) P= 10 N/ 0.2 m^2 = 50 N/m^2 = 50 Pa The equation for pressure can be rearranged to find force or area, as shown below... Force= Pressure x Area (rearrange by multiplying by area.) Area= Force/ Pressure (Rearrange by multiplying by area and then dividing by pressure.) Now you try: 1. Find the pressure exerted by a 3,000N crate hat has an area of 2 m^2.

2. Find the weight of a rock that has an area of 10 m^2 and that exerts a pressure of 250 Pa.

Quick Lab: Just for fun 1. Lay a EMPTY plastic bottle on its side. 2. Wad a small piece of paper (about 4cm x 4cm) into a ball. 3. Place the paper ball just inside the bottle's opening. 4. Blow straight into the opening. 5. Record your observations. 6. Explain your results in terms of high and low pressures.

Works Cited: **
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