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Pressure, Buoyancy, Floating, Sinking
Terms in this set (73)
What do you call a force exerted on a surface?
What is the relationship between pressure and area?
Pressure decreases as the area over which a force is distributed increases
How do you calculate the area of a rectangle?
multiply length & width
What formula can be used to summarize the relationship between force, area and pressure
Pressure= force divided by area
Which has a greater surface area, a sneaker or a snowshoe?
Will a sneaker or a snowshoe exert more pressure on snow?
the sneaker will exert more pressure on the snow because it has a smaller surface area
What is pressure?
force exerted on a surface divided by total area over which force is exerted
If you were designing a backpack that would lessen the amount of pressure on a student's back and shoulders, how could you change the size of the straps?
You would make the straps wider. Wider straps will have a larger surface area over which the force can be exerted. This will reduce the pressure on the student's back and shoulders.
What is the SI unit for force
What is the SI unit for area
square meters (m^2)
What is the SI unit of pressure? Another name for this unit?
N/m^2; Pascal (Pa)
What is a fluid?
a material that can easily flow (and change shape)
What are some examples of fluids that are liquids?
What are some examples of fluids that are gases?
What causes fluid air pressure
a) Particles in a fluid are constantly moving in all directions
b) As they move, they collide with each other and any surface they meet
c) As the particles collide with the surface, they exert a force on it
How would you determine fluid pressure?
the total force exerted by the fluid divided by the area over which it flows
Does air have mass?
How much mass does each cubic meter of air have?
What produces air or atmospheric pressure?
the weight of the air
In which direction does air exert pressure on an object?
in all directions
What would happen to a closed metal can if it were placed 6,000 meters below sea level?
It would be crushed because the pressure outside of the can is greater than the pressure inside the can
What would happen to a closed metal can if it were placed outside of the Earth's atmosphere?
It would explode/expand because the pressure outside of the can is less than the pressure inside the can
What happens to atmospheric pressure as elevation increases?
a) At what elevation do commercial airplanes fly?
b)How does the pressure at that elevation compare to that at sea level?
b) It is 20% of the pressure at sea level
a) What is the elevation of the highest point on Earth's surface?
b) How does the pressure of that elevation compare to sea level?
b) It is 30% of the pressure at sea level
What happens to water pressure as depth increases?
Water pressure increases as depth increases
What is the standard atmospheric pressure at sea level?
If a scuba diver went 10m below the surface, how would the pressure on him compare to the pressure at sea level?
The pressure on the diver is double the pressure at sea level
If a piloted submersible reaches a depth of 6500m, how would the pressure on the sub compare to the pressure at sea level?
The pressure on the submersible is 650 times greater than the pressure at sea level
Is the change in air pressure as elevation increases gradual or rapid?
Is the change in water pressure as depth increases gradual or rapid?
Sometimes scuba divers experience a dangerous condition known as "the bends" when they rise to the surface too quickly. Why do you think this occurs?
The pressure decrease too quickly causing the human to experience compressing and decompression sickness
Why do airplanes have pressurized cabins?
A pressurized cabin balances out the pressure outside the human body with the pressure within the human body
The total pressure at a given point beneath water is a result of the weight of what 2 things?
a) weight of the water above it
b) weight of the air above it
What instrument is used to measure atmospheric pressure?
What are the 2 types of barometers?
How do meteorologists use barometers?
they use them to predict the weather
What prediction could you make if the atmospheric pressure is decreasing rapidly?
a storm is on the way
What prediction could you make if pressure is increasing?
What 3 units are used for barometric pressure measurements?
What is the term used to describe the ability to float?
What is buoyant force?
the upward force exerted by a fluid on a submerged object
Why does a buoyant force make an object feel lighter?
the buoyant force acts in the direction opposite to the force of gravity
As depth in a fluid increases, what happens to pressure in the fluid?
How does the pressure on the bottom of a submerged object compare to the pressure on top of the object?
the pressure on the bottom is greater
In which direction is the net force on a submerged object?
In which direction is the force resulting from the weight of a submerged object?
What is the relationship between the buoyant force and the weight of an object that sinks?
the weight is greater than the buoyant force, causing the net force to be downward
What do you know about the net force on a submerged object if the weight of the object is equal to the buoyant force?
no net force acts on the object
How much fluid does a submerged object displace?
a volume of fluid equal to the volume of the submerged part
What does Archimedes' principle state?
the buoyant force acting on a submerged object is equal to the weight of the fluid the object displaces
If you are in a swimming pool and your body displace 50 liters of water, what is the buoyant force exerted on you?
50 liters of water, or about 500N
Does a large object or a small object displace more water?
The larger the object the more fluid is displaced
Does a greater buoyant force act on a large object or a small object?
a larger object experiences a greater buoyant force
Why does a ship float and a block of steel of the same weight sink?
a) a ship will displace more water than the block of steel because it is a larger object
b) since a ship displace more water than the block of steel, a greater buoyant force acts on the ship
c) A ship floats as long as the buoyant force acting on it is equal to its weight
If a boat developed a leak and some water entered the ship, use Archimedes' principle to explain why the boat might sink.
The added water would increase the ship's weight. If the weight of the ship and the added water exceeds the buoyant force the ship will sink (Titanic)
If you were designing a boat and you wanted to make it as buoyant as possible, how would you change the shape of the ship's hull?
You would make it wider so that it displaces more water
What is density?
a substance's mass per unit of volume
What is the formula used to calculate density?
Density = Mass divided by Volume
What is the density of water?
How can you predict whether an object will float or sink in a fluid?
by comparing the density of the object and the density of the fluid
What will the object do when placed in a fluid if its density is greater than that of the fluid?
it will sink
What will the object do when placed in a fluid if its density is less than that of the fluid?
it will float
What will the object do when placed in the fluid if its density id equal to that of the fluid?
the object will neither sink nor rise. It will float at a constant depth
Why does ice float in water if they are both water?
Water expands when it freezes, so ice occupies more space (has a greater volume). Therefore ice is less dense than water
Why is it that part of an iceberg is above water and part is below?
Because ice is only slightly less dense than water, most of the iceberg is below the water's surface.
How do you make a submarine dive?
a) water is taken into its tanks
b)As a result, mass increases, but volume is the same, causing density to increase
c) The weight of the sub becomes greater than the buoyant force
How do you make a submarine rise?
a) Compressed air is blown into the flotation tanks forcing the water out
b) As a result, mass decreases, but volume stays the same causing density to decrease
c) The weight of the sub becomes less than the buoyant force
What will the submarine do if its weight is greater than the buoyant force?
It will dive
What will the sub do if its weight is less than the buoyant force?
It will rise
What will the submarine do if its weight is equal to the buoyant force?
it will float at a constant depth
Why does a helium balloon rise?
Helium is less dense than the surrounding air
Why does a balloon filled with air sink or fall to the ground?
A balloon filled with air is denser than the surrounding air because air inside it is under pressure. The denser air, along with the weight of the balloon makes it fall to the ground.
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