64 terms

# Physics--Chapter 19: Liquids

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What is pressure?
force/area
What is the relationship between liquid pressure and depth of a liquid? Between liquid pressure and density?
liquid pressure increases with depth; it increases with density
By how much does the water pressure on a submarine change when the submarine dives to double its previous depth (neglect the very real effect of atmospheric pressure above)?
If the submarine operated in fresh water, would the pressure it feel be greater or less than at the same depth in salt water?
doubles
less because density of fresh water is less
How does water pressure 1 meter below the surface of a small pond compare with water pressure 1 meter below the surface of a huge lake?
same
If you immerse a tin can with a small hole in it in water so that water spurts through the hole, what will be the direction of water flow where the hole is?
perpendicular to the surface of the can
Why does the buoyant force act upward for an object submerged in water?
there is greater pressure against the bottom
How does the buoyant force that acts on a fish compare with the weight of the fish?
same
Why does the buoyant force on submerged objects not act sideways?
pressure on each side is the same
How does the volume of a completely submerged object compare with the volume of water displaced?
same
What is the mass of 1 liter of water in kilograms? What is its weight in newtons?
1 kg; 9.8 N
Does the buoyant force on a submerged object depend on the weight of the object itself or on the weight of the fluid displaced by the object?
Does it depend on the weight of the object itself or on its volume? Defend your answer.
Weight of fluid displaced
volume; the volume of the submerged object determines the volume of the fluid displaced
When the buoyant force on a submerged object is more than the weight of the object, how do the densities of the object and water compare?
object's density is less
When the buoyant force on a submerged object is less than the weight of the object, how do the densities of the object and water compare?
object's density is greater
What is the buoyant force that acts on a 100-ton ship?
100 tons
According to Pascal's principle, what happens to the pressure in all parts of a confined fluid when you produce an increase in pressure in one part?
Pressure increases equally in all parts
What are the key factors that determine the pressure exerted by the liquid?
density and depth
At, any point in a liquid, the forces that produce pressure are exerted in what way?
equally in all directions
Liquids have a net force that acts perpendicular to what?
the surface
At greater depths, the force what?
gets greater and the velocity of the escaping liquid is greater
Pressure of the liquid does NOT depend on what?
amount, volume, or total amount of liquid
The dam that must withstand the greater pressure is: the large, but shallow lake or the small, but deep lake??
small but deep lake...because it is the dam with the deepest water behind it, not the most water
When you are swimming in water, do you feel different amounts of pressure when you tilt your head on your ears?
no, you feel the same amount of water pressure on your ears because at any point within a liquid, the forces that produce pressure are exerted equally in all directions
the apparent loss of weight of an object when submerged in liquid
buoyancy
the upward force that acts in the opposite direction of gravity
buoyancy force
When the weight of a submerged object is equal to the buoyant force, the submerged object will...
remain at any level or will be suspended
A completely submerged object will always displace what kind of water?
displaces a volume of liquid equal to its own volume
What happens when there is a net upward force or a buoyant force?
the upward forces against the bottom of a submerged object are greater than the downward forces against the top...the forces acting horizontally against the sides cancel each other out
When the weight of a submerged object is greater than the buoyant force, the object will?
sink
When the weight is equal to the buoyancy force, the submerged object will?
remain at any level, like a fish
When the weight is less than the buoyant force, the object will?
rise to the surface and float
when water is pushed aside by an object
displaced
When a stone is placed in a container of water, the water level will?
rise
The volume of water displaced is equal to what?
the volume of the object
A completely submerged object always displaces a volume of liquid equal to what?
its own volume
What does Archimedes' Principle describe the relationship between?
buoyancy and displaced fluids
An immersed object is buoyed by a force equal to the weight of the fluid it displaces
Archimedes' Principle
can mean completely or partially submerged
immersed
True or False. The shape of the object changed the buoyant force equally the weight of liquid displaced.
False...this holds true at any depth
Archimedes' Principle holds true for what two things?
liquid and gases...both fluids
Any object with a volume of 1 liter will experience a buoyant force of what when completely submerged in water?
9.8 N
Is the weight of the displaced water or the the weight of the submerged object the buoyant force when an object is completely submerged?
the weight of the displaced water
According to Archimedes' Principle, what equals the weight of liquid displaced?
the upward force due to water pressure, minus the downward force due to water pressure on the top
Why does the depth of the submerged object make no difference?
because although there is more pressure at greater depths, the difference in pressures on the bottom and top of the block is the same at any depth
What are the 3 simple rules when it comes to sinking and floating?
1) an object more dense than the fluid in which it is immersed sinks
2) an object less dense than the fluid sinks
3) an object with equal density to the fluid neither sinks nor floats
the buoyant force on a submerged object depends on what?
volume, NOT WEIGHT...a smaller object displaces less water so has a smaller buoyant force acting on it...a larger object displaces more water so a larger buoyant force acts on it
What would happen if a fish were somehow bloated up?
Swallowed a stone?
-it would be less dense than the water and float to the top
-it would sink to the bottom
What do we say about people, who try but cannot float?
they are too dense...to float more easily, you must reduce your density...since weight density is weight divided by volume, you must eight reduce weight or increase volume...taking in a lung full of air can increase your volume...a life jacket would increase your volume but add little weight
How does a submarine control its density?
by controlling the flow water into and out of its ballast tanks
How does a fish regulate its density?
by expanding or contracting an air sac that changes its volume...a fish can move upward by increasing its volume which decreases density and downward by contracting its volume which increases density
How does a crocodile increase its density?
swallowing stones...with its increased density it can swim lower in the water and expose itself less to prey
a floating object displaces a weight of fluid equal to its own weight
Principle of Floating
True or False. Archimedes' principle holds true whether or not an object sinks or floats
true...in the case of floating, the buoyant force equals not only the weight of liquid displaced, but also the weight of the floating object
Why does a 1-ton iron block sink, while a 1-ton iron bowl float?
The iron bowl will still weigh 1 ton...but when you lower the bowl into a body of water, it displaces a greater volume of water than with the iron block...the deeper the bowl is immersed, the more water is displaced and the greater water equals the weight of the bowl, it will sink no further...it will float because the buoyant force now equals the weight of the bowl
What does Pascal's Principle deal with?
the transfer of pressure through enclosed fluid objects
Changes in pressure at any point in an enclosed fluid at rest are transmitted undiminished to all points in the fluid and act in all directions
Pascal's Principle
Are the ideas of efficiency compromised?
No, the law of conservation of energy is not compromised...the increase in force is compensated for by a decrease in distance moved
Where is Pascal's Principle implemented in?
hydraulic press
What does Pascal's Principle apply to?
all fluids whether gases or liquids
What is a typical application of Pascal's Principle for gases and liquids?
automobile lift...compressed air exerts pressure on the oil in an underground reservoir. the oil in turn transmits the pressure to a cylinder, which lifts the automobile
the top floor of a building is 30 m above the basement. calculate how much greater the water pressure is in the basement compared with the pressure at the top floor
1000 x 9.8 x 30= 2.9 x 10^5 Pa
Why does water seek its own level?
water wants to have equal pressure, but pressure is already equal in all directions
why is it inaccurate to say that heavy objects sink and light objects float?
depends on density of object compared to fluid it was put into
compared with an empty ship, would a ship loaded with a cargo of foam insulation sink deeper into water or rise in water?
sink deeper because it is adding mass without any volume
A) a half-filled bucket of water is on a spring scale. If a live fish is placed in it, what happens to the reading on the scale?
B) Would your answer be different if the bucket were initially filled to the brim?
A) yes, increase by the weight of the fish
B) yes, the weight of the fish will fall out of the top of the fish