SPH 4CHydrostatic Pressure & FLUID MOTION

Review - Answers

  1. What is the definition of a fluid in motion? Give two examples of a moving fluid.

A fluid in motion is either liquid or gas that moves over time.

eg. air over a car, water in a pipe

  1. Define these terms, and provide a diagram and an example for each:

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  • Boundary layer

thin layer of fluid that sticks to the surface that the fluid is passing

eg. over an aerofoil (wing)

  • Laminar flow

smooth flow of a fluid

eg. air over a streamlined body

  • Turbulent flow

non-smooth flow of a fluid

eg. swirling vapour trails at the wing tips of an airplane

  • Boundary layer separation

when fluid doesn’t stick to the surface

eg. turbulence behind a golf ball, causing drag

  • Magnus effect

lift force on a spinning object in a moving fluid

eg. curve ball

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  1. What is the basic formula for determining pressure that involves area and force? What is the unit for pressure?

1 Pascal (Pa) = 1 Newton / metre2 (N/m2)

  1. a) Describe Pascal’s Principle.

pressure of a fluid in a closed container is equal everywhere and in all directions

A hydraulic lift has these specifications:

Effort piston radius:5 cmLoad piston radius:30 cm

Max. load:5000 N

b)What is the pressure inside the load cylinder?

17683.9 Pa – remember that the cylinder has a circular end area

c)What is the pressure inside the effort cylinder? What is the area of the effort piston?

17683.9 Pa0.00785 m2

d)How much force must be applied at the effort cylinder to achieve lift the maximum load at the other piston?

139 N

e)What is the ideal mechanical advantage of this hydraulic lift? The AMA?

3636

  1. If a tank of compressed gas is connected to a U-tube manometer, it supports 12 cm of mercury (mercury = 13 600 kg/m3). What is the gauge pressure inside the tank? (16 kPa)
  1. Calculate the hydrostatic pressure of a column of water that is 15 m high.(147 kPa)
  1. How and why does turbulence cause aerodynamic drag?
  1. Describe the Bernoulli Principle. Use it to explain why two pop cans on rollers go together when air is blown between them.
  1. A ping pong ball is suspended by string and brought near a stream of falling water. If the ball is brought close enough to the water, without actually touching it, what will happen? Why? Draw a diagram to help explain. What other everyday occurrence is like this?
  1. How does a curve ball work? Sketch a diagram showing the airflow around the ball and the pressures. Whose effect provides an explanation for this? (Magnus)
  1. Why are there dimples on a golf ball? What do they help the golfer do with the ball (2 things)?

(go further; control spin)

  1. How does a liquid lawn fertilizer attached to your garden hose use the Bernoulli Principle?
  1. Give two (2) ways that engineers have developed more streamlining in their designs of vehicles. What advantages does streamlining a vehicle provide? (less drag; better fuel consumption)
  1. a) Identify each of the symbols below from a hydraulic circuit.

b)What is the function of the relief valve?

  1. Describe the features that reduce drag on the luge toboggan and rider in the figure to the right.
  1. Answer these questions from the textbook:

p. 261 #5

p. 274 #18

p. 300 #14, 19

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