Chapter 7 - Holt Forces in Fluids

Section 1 pages A fluid is any material that can flows and that takes the shape of its container. Fluids include liquids, such as water and oil, gases such as oxygen and carbon dioxide.

Fluids are able to flow because the particles in fluids, unlike the particles in solids can move easily past each other.

The following equation can be used to find the pressure, or rearranged to find force or area. Pressure = Force / Area The SI unit for pressure is the pascal

Why are bubbles round?

Why do your ears ‘pop’ when you are in a plane taking off or in a car travelling down a steep mountain road?

The pressure caused by the weight of Earth’s atmosphere is called atmospheric pressure. Fluids exert pressure equally in all directions

Fluid pressure increases as depth increases. Fluids flow from areas of high pressure to areas of low pressure.

Pascall’s Principle states that a change in pressure at any point in an enclosed fluid will be transmitted equally to all parts of the fluid. Hydraulic devices transmit changes of pressure through liquids.

Section 2 pages Any object that is more dense than the surrounding fluid will sink. Any object that is less dense than the surrounding fluid will float.

All fluids exert an upward force called buoyant force, which is caused by differences in fluid pressure.

Archimedes Principle states that the buoyant force on an object is equal to the weight of the fluid displaced by the object.

Section 3 pages Bernoulli’s Principle states that fluid pressure decreases as the speed of a moving fluid increases.

Concerning flight. Wings are often shaped to allow airplanes (and birds) to take advantage of decreased pressure in moving air in order to achieve flight.

Lift is an upward force that acts against gravity. Drag opposes motion through fluids

Lift on an airplane is determined by wing size and thrust. Thrust is the forward motion produced by the engine of an airplane.

questions 1. Compared with an empty ship, will a ship loaded with plastic-foam balls float higher or lower or the same level in water? Explain your answer.

1. Answer: The ship will float lower in the water because the plastic-foam balls will add to the total mass of the ship, but will not increases the volume. Therefore the overall density will increase, causing the ship to sink a little.

2. If an object weighing 50 N displaces a volume of water with a weight of 10 N, what is the buoyant force on the object? Show your equation and work.

2. Answer: The buoyant force is equal to the displaced water force. Therefore, the buoyant force = 10N

3. A helium-filled balloon will float in air because helium gas is less dense than air. Even though the balloon also has mass, the helium plus the balloon mass/volume is less than air.

4. Where is water pressure greater? At a depth of 1 m in an ocean, or, at a depth of 2 m in a small pond? Explain your answer.

4. Answer: Pressure increases with depth, regardless of the amount of the fluid pressure. Therefore, the water pressure is greater at a depth of 2 m in a small pond.

Inside all vacuum cleaners is a high- speed fan. Explain how this fan causes dirt to be picked up by the vacuum cleaner.

Look at Interpreting Graphics page 181. Answer questions 21,22,23,24 concerning icebergs.

Answers: 21. Water pressure is the greatest on the iceberg at point c (bottom of iceberg)

22. Answer: The section form b-c (submerged) of the iceberg has a weight equal to the buoyant force.

23. Answer Ice is less dense than water (it has air trapped inside)

24. Answer Icebergs are so dangerous to passing shops because only a small portion floats above the surface of the water and is visible. Therefore, the chance of running into the iceberg portion underneath the surface is greater since it cannot be seen, and could scrape the hull.

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