Pressure and pressure differences in fluids (5.5) (M) Flashcards
What can a fluid be?
either a liquid or a gas
What does the pressure in fluids cause?
a force normal (at right angles/perpendicular) to any surface
Why does the pressure of a liquid increase with depth?
Because as depth increases, there is a greater volume of water above a person,
Why does the pressure of a liquid increase with density?
As density increases, there is greater weight acting downwards
Why are the walls of a dam thicker at the bottom?
There is a greater pressure of liquid at the bottom, as the depth is greater, and therefore there is a greater weight of liquid acting downwards
Why does a partially (or totally) submerged object rise and float?
The object experiences a greater pressure on the bottom surface than on the top surface
This creates a resultant force upwards
This force is called the upthrust
When can an object float?
When the upthrust force equals the object’s weight
When does an object sink?
When the upthrust force is less than the object’s weight
Describe the relationship between upthrust and weight of water displaced
The size of the upthrust acting on the object is the same as the weight of water displaced by the object
so it can float
Why does an object with a greater density than water sink?
The object cannot displace a volume of water equal to its own weight
So weight of the object is greater than the upthrust and so the object sinks
Describe the observation for an object with the same density as water floating?
The surface of the object is at the surface of the water
this will have to displace more water than an object with a lower density
How does a greater surface area affect whether an object can float?
there is more surface area to distribute the weight across and displace the water, so it will float
What is the atmosphere?
a thin layer (relative to the size of the Earth) of air round the Earth
The atmosphere gets (…) dense with increasing altitude
less
How is atmospheric pressure created?
Air molecules colliding with a surface
important to learn
Why does atmospheric pressure decrease with an increase in height?
Air molecules colliding with a surface creates pressure
At increasing altitude distance between molecules decrease or at increasing altitude, there are fewer molecules (above a surface)
so the number of collisions with a surface decreases or so always less weight of air than blow (the surface)
Why must aircraft that fly at high altitudes be pressurised?
If the air pressure is too low, humans cannot take in oxygen quickly enough to meet their bodies’ needs
2 needed
What are the factor that influence floating and sinking?
- density
- surface area
Other than weight, what other force may act downwards on an object?
drag
Why does water sometimes exert upthrust on an object?
Pressure acting on the bottom of the object greater than the pressure acting on top
A hole is made in a bottle of water, explain why, as the volume of the water decreases, the jet of water coming from the hole travels a shorter distance?
The pressure at the hole decreases
So the water exits at a lower speed
Why the further a swimmer dives below the surface of a swimmer, the greater the pressure on the swimmer?
Increasing depth increases the volume of water above the swimmer, so increases the weight acting on the swimmer
Velocity is (…) in shallow water
slower
and converse
What can be concluded from this model about pressure in a liquid?
Pressure (in a liquid) acts in all directions
