P11 - Force and Pressure Flashcards
What is upthrust?
the upward force that acts on a body partly or completely submerged in a fluid
What is pressure?
The force per unit area
What unit is used to measure pressure?
pascals (N/m²)
Pressure along a horizontal line in a liquid is ……….
constant
Pressure in a liquid ……….. with depth
increases
What is the equation for pressure in a liquid?
pressure = height x density x gravitational field strength
Why does water pressure increase with depth?
Because there is a greater weight of water above it
What is atmospheric pressure?
air molecules collide with surfaces and exerts a small amount of force on it, the number of molecules colliding with a surface per second is very large so there is a larger force exerted
Why does atmospheric pressure decrease with altitude?
Because there is a lower weight of air above you, the air is less dense at higher altitudes. This causes there to be fewer molecules per cubic feet and therefore reduces the number of collisions per second
Why is the air less dense at higher altitudes?
At increased altitudes, there is less weight of air above, so atmospheric pressure decreases with increasing altitude
The more an object is submerged in water, the ……….. the volume of water is displaced and upthrust …………….
bigger, increases
An object floats when ……………..
Its weight is equal to upthrust
An object sinks when ………………
Its weight is greater then the upthrust
An object that is more dense than the liquid sinks because …………………..
Its weight is greater than the weight of the liquid displaced. So the weight of the object is greater than the upthrust on the object when it is fully immersed
An object that is less dense than the liquid floats because …………………..
Its weight is less than the weight of the liquid it displaces. So the weight of the object is less than the upthrust on the object when it is fully immersed
A fully immersed object displaces:
an equal volume of water as said object
What is pascals principle?
pressure = force / area
If a denser liquid is used in a manometer h will …………….
decrease
What do manometers do?
They measure a pressure difference by balancing the weight of a fluid column between 2 pressures of interest
What are small pressure differences measured with in a manometer?
Lighter fluids, such as water
What are large pressure differences measures with?
denser and heavier fluids, such as mercury
What does a Manometer consist of?
a U-tube of liquid
How does a manometer work?
The liquid moves until the pressure difference between the gases is balanced by the pressure exerted by the higher column of liquid. The greater the pressure difference, the greater the height difference
