Chapter 3 – Forces in Fluids

1. Chapter 3 – Forces in Fluids Section 1

2. Fluids and Pressure What is a fluid? Fluid – any material than can flow and that takes the shape of its container. What are some examples?

3. Pressure • What types of pressure are there? • Air pressure Pressure – the amount of force exerted on a given area. Pressure = force/area SI unit for pressure is Pascal.

4. Pressure = force/area The force of air in a balloon is 2N and the area of the balloon is 2m2. What is the pressure exerting on the inside of the balloon?

5. Why are bubbles round? The air in the bubble exerts pressure evenly in every direction, so the bubble expands in every direction.

6. Atmospheric Pressure The weight of the atmosphere due to gravity pulling it to the earth. Atmosphere is made up of: Nitrogen, Oxygen, and other gases. The atmosphere exerts a pressure of approximately 101,300 N on every square meter. Also known as 101,300 Pa

7. So that means: 10N (the weight of pineapple) is applied on every square centimeter (roughly the area of the tip of your little finger) of your body. Why doesn’t this hurt? Because the fluids inside your body also exert pressure.

8. Atmospheric Pressure Varies Depending on your elevation atmospheric pressure changes. On top of Mount Everest the atmospheric pressure is 33,000 PA. The pressure increases as the atmosphere gets “deeper.”

9. If you travel to higher or lower points in the atmosphere the fluids in your body have to adjust to maintain equal pressure. Just like when your ears “pop” in an airplane. Small pockets of air behind your eardrums contract or expand as atmospheric pressure increases or decreases. “pop” occurs when air is released due to these pressure changes.

10. Review How do particles in a fluid exert pressure on a container? Why are you not crushed by atmospheric pressure? Explain why dams on deep lakes should be thicker at the bottom than near the top.

11. Water Pressure Water pressure increases with depth because of gravity. The greater a diver goes in water the greater the pressure becomes because more water above the diver is being pulled by Earth’s gravitational force.

12. Density Is the amount of matter in a certain volume. Water is more dense than air. Water exerts more pressure than air. If you climb up a tree 10 meters and then you dive 10 meters underwater. Where would you have the greater pressure exerted on you?

13. Fluids Flow from High Pressure to Low Pressure • When drinking through a straw: • You remove the air from the straw and reduce the pressure in the straw. What you are drinking has the greater pressure so the liquid moves up the straw. The outside pressure forces the liquid up the straw along with the suction you are creating in the straw.

14. When breathing: • When you inhale a muscle increases the space in your chest, giving your lungs room to expand. This expansion lowers the pressure in your lungs so that it becomes lower than the outside air pressure. • Air then flows into your lungs from higher pressure to lower pressure.

15. Pascal’s Principle Blaise Pascal, 17th century French scientist. Pascal’sPrinciple – a change in pressure at any point in an enclosed fluid will be transmitted equally to all parts of that fluid.

16. Putting Pascal’s Principle to Work Hydraulic – devices that use liquids to transmit pressure from one point to another. Ex. Hydraulic Brakes: Driver’s foot exerts pressure on a cylinder of liquid. Pascal’s principle tells you that this pressure is transmitted equally to all parts of the liquid-filled brake system. This liquid presses a brake pad against each wheel, and friction brings the car to a stop.

17. Review Explain how atmospheric pressure helps you drin k through a straw. What does Pascal’s principle state? When you squeeze a balloon, where is the pressure inside the balloon increased the most? Explain your answer in terms of Pascal’s principle.