Chapter+9+Fluids

Patrick Yang Chapter 9 Fluids

Formulas and Critical thinking problems: What happens to the density of a balloon if the volume is doubled but the mass remains the same? Explanation: The density is halved because it is inversely related to the volume of the balloon. What happens to the pressure on your feet if you wear high heels? Explanation: The pressure increases because the weight of your body (which is a force) is spread out across a smaller area. What happens to a scuba diver as they descend into the ocean? Explanation: H increases, so the pressure on a scuba diver increases significantly the further they go down. This is why they need to breathe pressurized air and prepare their bodies for the physical stress. Why does some wood float in water? Explanation: Woods that are less dense than water float due to the buoyant principle; the volume of water required for the buoyant force to counteract the force of gravity is not enough to submerge a plank of wood. What happens when you pinch a running hose? Explanation: People often pinch a running hose to squirt someone unexpectedly. The pinch decreases the area of the opening where the water flows out, therefore giving the water the velocity to reach unsuspecting people at long distances. Why does a swiftly moving fluid exert less pressure than a slowly moving fluid? Explanation: This application of Bernouli's principle comes from the conservation of energy. Since changes in pressure times volume and kinetic energy are both the result of work done on the fluid, they must have an inverse relationship when the fluid experiences zero net work.

Vocab: Density - mass per unit volume Pressure- Force per unit area that a fluid exerts on an object in it Pascal's principle - when pressure is applied to an enclosed fluid, the pressure is transmitted undiminished to every point of the fluid and to the walls of the containing vessel Buoyant force - The force a fluid exerts on an object submerged, which is equal to the weight of the displaced fluid Archimedes' principle - describes the buoyant force Equation of continuity - describes the rate of flow of a fluid as area changes Bernouli's equation - results in statement that swiftly moving fluids exert less pressure than do slowly moving fluids

1) A container is filled to a depth of 20 cm with water. On top of the water floats a 30 cm think layer of oil with specific gravity of 0.700. What is the absolute pressure at the bottom of the container? a) 1 x 10^3 Pa b) 2 x 10^3 Pa c) 1.04 x 10^5 Pa d) 1.05 x 10^5 Pa

2) A wooden block of volume 5.24 x 10^-4 m^3 floats in water, and a small steel object mass 0.31 kg is placed on top in equilibrium. If the top of the wooden block is at the level of the water, what is the density of the wood? a) 346 kg/m^3 b) 391 kg/m^3 c) 408 kg/m^3 d) 411 kg/m^3

3) If the wood in question two has a density of only 300 kg/m^3, what must the mass of a new steel object be so that the wood is at the level of the water? a) 0.412 kg b) 0.422 kg c) 0.476 kg d) 0.504 kg

4) A jet airplane in level flight has a mass of 8.66 x 10^4 kg and the two wings have an estimated total area of 90 m^2. What is the pressure difference between the lower and upper wing surfaces? a) 9.02 x 10^3 Pa b) 9.43 x 10^3 Pa c) 9.58 x 10^3 Pa d) 9.64 x 10^3 Pa

5) If the speed of the air under the wings in question 4 is 225 m/s, what is the speed of the air over the wings? (Hint: air has a density of 1.29 kg/m^3.) a) 245 m/s b) 252 m/s c) 255 m/s d) 260 m/s

media type="youtube" key="lWDtFHDVqqk" height="315" width="420" Part 2 of a 12 part series.

Answers to multiple choice: d, c, b, b, c