# Fluids

## Terms

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- What type of fluid is compressible and has a volume that can be easily changed?
- Gas
- What is a FLUID?
- A substance that can easily flow - a liguid or a gas.
- What is a HYDRAULIC SYSTEM?
- A device that uses Pascal's principle to apply a force to a small surface area which transmits an increase in pressure through a confined fluid that exerts a larger force over a larger surface area.
- What is ARCHIMEDE'S PRINCIPLE?
- The buoyant force on an object is equal to the weight of the fluid displaced by the object.
- If each cubic meter of air around us has a mass of about 1 kilogram and the atmosphere is over 100,000 meters high, why aren't we crushed by the weight of the atmosphere?
- ... because in a fluid such as air that is not moving, pressure at any point is exerted equally in all directions.
- What is an AIRFOIL?
- A shaped surface designed to provide lift.
- The brake system of a car is operated by what kind of device using Pascal's principle?
- hydraulic system
- If the weight of an object in a fluid is less than the buoyant force, what will it do?
- Float.
- What law of motion explains why fluid pressure is exerted equally in all directions in a stagnant fluid?
- Newton's third law of motion
- An object immersed in a fluid sinks to the bottom. Does the object or fluid have a greater density or are their densities the same?
- The object has a greater density.
- What type of fluid is not compressible, takes the shape of its container, and has a volume that can not be changed?
- Liquids
- For an object floating on a surface, what is the volume of the fluid displaced equal to?
- ... the volume of the part of the object that is submerged under the fluid.
- What happens to air pressure as elevation increases?
- Air pressure decreases.
- An object immersed in a fluid rises to the surface and floats. Does the object or fluid have a greater density or are their densities the same?
- The fluid has a greater density.
- What happens to water pressure as depth increases?
- Water pressure increases as depth increases.
- If the weight of an object in a fluid is greater than the buoyant force, what will it do?
- Sink
- What is PRESSURE?
- Force per unit area.
- What is BERNOULLI'S PRINCIPLE?
- The pressure exerted by a moving stream of fluid is less than the pressure of the surrounding fluid.
- What is the standard international (SI) UNIT of PRESSURE?
- pascal (Pa)
- What force present on an object under water causes it to feel lighter than in air?
- buoyant force
- What two things add to the total pressure underwater at a certain point?
- ... the pressure of the water above this point plus the air pressure above the water.
- When there is a difference in fluid pressure, what is the direction of flow of the fluid?
- ... from high pressure to low pressure.
- In terms of SI units of force and area, how is one pascal expressed?
- Pa = N/m2
- What is a BUOYANT FORCE?
- A force that acts on an object in a fluid that opposes gravity.
- What is PASCAL'S PRINCIPLE?
- When force is applied to a confined fluid, an increase in pressure is transmitted equally to all parts of the fluid.
- What is DRAG?
- ... the air friction on a wing as it moves through the air.
- An object immersed in a fluid neither rises to the surface nor sinks, but floats at a constant level. Does the object or fluid have a greater density or are their densities the same?
- The densities of the object and fluid are the same.
- What principle explains why we are able to breathe by expanding our lungs (inhaling) and contracting them (exhaling)?
- Bernoulli's principle
- What is DENSITY?
- The mass per unit volume of a substance.
- If the weight of an object in a fluid is equal to the buoyant force, what will it do?
- The object will remain at some level in the fluid where the total upward force of buoyancy is equal to the total downward force of the weight the fluid above the buoyant force which it has to support.
- Using Bernoulli's principle, why does air flow faster above the wings of a plane than below?
- Wings are designed to have air flow more quickly over them than under them so that the difference in pressure will result in a net force upward, helping to lift or support the plane.
- What is LIFT?
- The upward force exerted on a wing caused by the fluid pressure being lower on its top side than underneath.