1. Science ace - Pressure Done by: David Li (09) 2P3

2. Types of pressure In these slides, I will be focusing on fluid pressure (water pressure) and atmospheric pressure (air pressure).

3. Definition of pressure Pressure is an effect which occurs when a force is applied on a surface. Pressure is the amount of force acting on a unit area.

4. The formula of Pressure P=F/A where P is the pressure, F is the normal force, and A is the area.

5. SI unit for pressure The SI unit for pressure is the Pa(Pascal), equal to one Newton per square meter (N/m2 or kg·m−1·s−2)

6. What is water pressure? Water pressure comes from the weight of the water overhead. The weight of the water depends on the height of the water column. So the deeper you are, the more the water above you weighs and the greater is the water pressure.

7. Examples of water pressure -water pumps These pumps work by spinning water around in a circle inside a cylindrical pump housing. The pump makes the water spin by pushing it with an impeller. The blades of this impeller project outward from an axle like the arms of turnstile and, as the impeller spins, the water spins with it. As the water spins, the pressure near the outer edge of the pump housing becomes much higher than near the centre of the impeller.

8. Examples of water pressure -Drinking from a straw When you drinking through a straw, you are removing some air from the space inside the straw and above the water, so that the air pressure in that space drops below atmospheric pressure. The water column near the bottom of the straw then experiences a pressure imbalance: the usual atmospheric pressure below it and less-than-atmospheric pressure above it. That imbalance provides a modest upward force on the water column and pushes it up into your mouth. But if you make that straw longer, you'll need to suck harder. That's because as the column of water gets taller, it gets heavier. It needs a more severe pressure imbalance to push it upward and support it

9. Examples of water pressure -Scuba diving You can only go a few feet under water before you'll no longer be able to draw air into your lungs through that hose. The water pressure outside your chest increases rapidly as you go deeper, but the air pressure inside the hose and your mouth barely changes at all. Pretty soon, you'll have so much more pressure outside your lungs than inside them that you won't be able to draw in any more air. Your muscles just won't be strong enough.

10. Atmospheric pressure The pressure exerted by the weight of the atmosphere. At sea level has a mean value of 101,325 Pascal.

11. Effects of atmospheric pressure Our body have natural pressure within it, therefore we will not be crushed by the force of the atmospheric pressure, which is approximately 1 ton.

12. Showing the presence of atmospheric pressure Tie a piece of string around the middle of a stick of piece of cane so that it balances. Then tie an empty balloon to each end of the cane. The two balloons .the piece of change should still be balanced. Now remove one balloon and blow air into it. When you have done that, tie it back onto the end of the cane. Is there any change? The end with the blown-up balloon on it should dip downwards. This is because the air in the balloon is making it heavier, should balance evenly at each end.

13. Proving the presence of atmospheric pressure. How a syringe works is similar to drinking with a straw. To fill the syringe with liquid, we pull the plunger upward. This acting on the liquid surface, which is greater than the pressure in the barrel, pushes the liquid into barrel.

14. Video This is my homemade video. It is about atmospheric pressure. Please click on it to start.

15. Biblography http://en.wikipedia.org/wiki/Water_pressure#Fluid_pressure http://www.newton.dep.anl.gov/askasci/gen99/gen99171.htm http://www.wellowner2.org/2009/index.php?option=com_content&view=category&layout=blog&id=23&Itemid=22 http://www.howeverythingworks.org/water_distribution.html http://www.rcn27.dial.pipex.com/cloudsrus/pressure.html