 # Fluids, Gases & Heat Flashcards Preview

## AP Physics > Fluids, Gases & Heat > Flashcards

Flashcards in Fluids, Gases & Heat Deck (133):
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## How is the buoyancy force of a submerged object calculated? ### The buoyancy force of a submerged object is simply the weight of the liquid displaced by the portion of the object that is submerged. FB = ρliq * Vsub* g Where: FB = the buoyancy force pushing up on the object ρliq = the density of the liquid Vsub = the volume of the object that is submerged in the liquid g = the gravitational acceleration (commonly 10 m/s2) 10

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## A cube of styrofoam, with a density of 0.5 g/cm3, is dropped into water. How much of the cube is submerged in the water when the cube begins to float? ### One half of the cube will be submerged in the water. The proportion of an object that is under the surface of a liquid when the object floats is simply equal to ρobj/ρliq, where ρobj is the object's density and ρliq is the liquid's density. In this case, the object is one-half the density of the liquid, and thus one-half of it will be submerged when it floats. Note that if ρobj > ρliq, this fraction is greater than 1, and the object sinks to the bottom. 14

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## What does Pascal's Law predict about the pressure on plates 1 and 2 in the diagram below? ### Pascal's Law predicts that the pressures will be equal. The force F1 will be exerted on the fluid behind plate 1 as a pressure P1. The fluid will exert that pressure, undiminished, on all the walls it is contacting, including plate 2. 19

## How does the force F2 change if plate 2 in the hydraulic lift pictured below doubles in area? ### The force F2 doubles. According to Pascal's Law, the pressures on plates 1 and 2 must be equivalent. From the definition of pressure, therefore: P1 = F1/A1 = F2/A2 = P2 So force and area are directly proportional, and doubling A2 will double F2 as well. 20

## How does the distance D2 compare to the distance D1 if plate 2 in the hydraulic lift pictured is double the area of plate 1? ### D2 = ½D1. Since the liquid between the plates in incompressible, the volume displaced by plate 1 must be equal to the volume displaced by plate 2: V1 = A1D1 = A2D2 = V2 So distance and area are inversely proportional, and a plate of double the area will move half the distance. 21

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## How does the speed of a fluid flowing through a pipe change, as the diameter of the pipe decreases? ### As pipe diameter decreases, fluid flowing through the pipe begins to flow faster. This is akin to placing your thumb partially over the end of a water hose, which causes the water to flow through faster, creating a jet of water. 29

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## How much does the length of an object change when its temperature changes?

### An object's length change depends on its coefficient of thermal expansion: ΔL/L =αL ΔT Where: L = the object's original length ΔL = the change in the object's length αL = the object's coefficient of thermal expansion ΔT = the change in temperature 41

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## a material's standard enthalpy of formation, ΔHof

### The standard enthalpy of formation (ΔHof) is the enthalpy change of the formation reaction for the material from its fundamental elements under standard conditions. Ex: The enthalpy of formation for NaCl is  -411.12 kJ mol−1 and follows from the general equation: 72

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## The curve below represents a sample's temperature vs. heat added. What phases (solid, liquid, and/or gas) are present at each labeled point on the plot?  89

## The curve below represents a sample's temperature vs. heat added. What heat (q) formula would need to be applied, in order to calculate heat added to the system at each labeled point on the plot?  90

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