Lecture 9 - Supplement CHAPTER 12 Fluid Mechanics Pressure

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PHY 2048

• Lecture 9 - Supplement

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CHAPTER 12
Fluid Mechanics
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Pressure at the top of the liquid (oil and water)
are the same and equal to the atmospheric
pressure, P0
Pressure at the bottom of the pipe where the oil
and water meet is P
P P0 ?water hwater g
P P0 ?oil hoil g
?water hwater ?oil hoil
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What is the distance between the top of the wood
cube (after it has come to rest) and the
interface between the oil and water?

• The buoyancy force comes from two parts
• Upward force due to displaced oil
• Upward force due to displaced water

The volume of the block is L3
The volume of displaced oil is L2d
The volume of displaced water is L2(L-d)
The block is in equilibrium
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CHAPTER 15
Mechanical waves
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A fisherman notices that his boat is moving up
and down periodically without any horizontal
motion, owing to waves on the surface of the
water. It takes a time of 2.70 s for the boat to
travel from its highest point to its lowest, a
total distance of 0.600 m. The fisherman sees
that the wave crests are spaced a horizontal
distance of 5.80 m apart.
The amplitude of the wave is half the total
distance moved from the highest point to the
lowest and this is 0.300 m
The period of the wave is the time taken to go
from the highest point to the lowest and back
again to the highest point and this is 5.40 s
The distance between two identical points on a
wave (say the crest) is the wavelength which in
our case is 5.80 m
The speed of the wave is (5.80 m)/(5.40 s) 1.07
m/s