Find: Explain and give examples.

Problem 1.1 [Difficulty: 3]

Given: Common Substances

Tar Sand “Silly Putty” Jello Modeling clay Toothpaste Wax Shaving cream

Some of these substances exhibit characteristics of solids and fluids under different conditions.

Find: Explain and give examples.

Solution: Tar, Wax, and Jello behave as solids at room temperature or below at ordinary pressures. At high pressures or over long periods, they exhibit fluid characteristics. At higher temperatures, all three liquefy and become viscous fluids.Modeling clay and silly putty show fluid behavior when sheared slowly. However, they fracture under suddenly applied stress, which is a characteristic of solids.Toothpaste behaves as a solid when at rest in the tube. When the tube is squeezed hard, toothpaste “flows” out the spout, showing fluid behavior. Shaving cream behaves similarly.Sand acts solid when in repose (a sand “pile”). However, it “flows” from a spout or down a steep incline.(Fox and McDonald's Introduction to Fluid Mechanics 9e Philip Pritchard, John Mitchell) (Solution Manual, For Complete File, Download link at the end of this File) 1 / 4

Problem 1.2 [Difficulty: 2]

Given: Five basic conservation laws stated in Section 1-4.

Write: A word statement of each, as they apply to a system.

Solution: Assume that laws are to be written for a system.

• Conservation of mass — The mass of a system is constant by definition.
• Newton's second law of motion — The net force acting on a system is directly proportional to the product of the

system mass times its acceleration.

• First law of thermodynamics — The change in stored energy of a system equals the net energy added to the

system as heat and work.

• Second law of thermodynamics — The entropy of any isolated system cannot decrease during any process

between equilibrium states.

• Principle of angular momentum — The net torque acting on a system is equal to the rate of change of angular

momentum of the system. 2 / 4

Problem 1.3 [Difficulty: 3]

Open-Ended Problem Statement: The barrel of a bicycle tire pump becomes quite warm during use.Explain the mechanisms responsible for the temperature increase.

Discussion: Two phenomena are responsible for the temperature increase: (1) friction between the pump piston and barrel and (2) temperature rise of the air as it is compressed in the pump barrel.Friction between the pump piston and barrel converts mechanical energy (force on the piston moving through a distance) into thermal energy as a result of friction. Lubricating the piston helps to provide a good seal with the pump barrel and reduces friction (and therefore force) between the piston and barrel.Temperature of the trapped air rises as it is compressed. The compression is not adiabatic because it occurs during a finite time interval. Heat is transferred from the warm compressed air in the pump barrel to the cooler surroundings.This raises the temperature of the barrel, making its outside surface warm (or even hot!) to the touch. 3 / 4

Problem 1.4

(Difficulty: 1)

Given: Data on oxygen tank.

Find: Mass of oxygen.

Solution: Compute tank volume, and then us e oxygen density to find the mass.

The given or available

data is:

D = 16⋅ft p = 1000⋅psi T = (77 + 460)⋅R T = 537⋅R

For oxygen the critical temperature and pressure are: T

c = 279⋅R p c = 725.2 ⋅psi (data from NIST WebBook)

so the reduced temperature and pressure are:

Using a compressiblity factor chart: Z = 0.948 Since this number is close to 1, we can assume ideal gas behavior.

Therefore, the governing equation is the ideal gas equation p = ρ⋅R

O2 ⋅T

M and ρ = V

where V is the tank volume V = 3

π⋅D

6

V = π × (16⋅ft) 3

6

V = 2144.7 ⋅ft 3

• / 4