Pressure Flashcards
(30 cards)
Pressure
-force per unit area
-determines the effect of a force on a surface
Shoe example:
Flat shoes spread the force over a large area so the pressure…
….is reduced.
-snow shoes have larger area than feet and spread force over more area, reducing pressure on snow which stops ppl sinking
Why will it hurt more if a person steps on a foot in high heels than in flats?
-high heeled shoes transfer the force through a much smaller area
-causing greater pressure
Fluid
-substance that can flow, such as liquid or gas
What type of force does the pressure in fluids cause to a surface?
-force normal
What is a force normal?
-force that acts 90 degrees to a surface
Pressure equation
p (Pa) = F(N) / A (m squared)
Pressure in fluids example question:
A fluid exerts a force of 150 N over an area of 1.2 m2 Calculate the pressure on the surface
150N/1.2m2
=125Pa
What happens to pressure in a liquid at different depths?
-pressure increases as the depth increases
-this is because the deeper you go, the more column of water there is above the area
-the weight increases, which increases pressure
Why does pressure act in all directions?
-particles in fluids move randomly and collide with surfaces from every angle
-collisions generate a force that spreads equally in all directions, rather than in just one
Explain why dam walls are usually wedge-shaped
-pressure is greater at the bottom, so the walls need to be stronger there
-this is because the more column of water there is above, the more weight there is
Pressure in a fluid calculation:
pressure (Pa) = height of column (m) × density of the fluid (kg/m3) × gravitational field strength (N/kg)
Pressure in a liquid example question:
A stone is dropped into a lake. Calculate the increase in pressure on the stone caused by the water when it sinks from 1 m deep to 6 m deep. (The density of water is 1,000 kg/m3 and gravitational field strength is 9.8 N/kg).
1000kg/m3 x (6-1)m x 9.8 N/kg =
49000Pa
What is the atmosphere?
-thin layers of gases that surround the Earth
Key features of the atmosphere
-thin compared to the size of the Earth
-becomes less dense as the altitude increases
Explain why atmospheric pressure with an increase in height
-number of air molecules (and so weight of air) above the surface decreases as the height of the surface above ground increases
-so there are less molecules they collide with eachother less frequently and exert less pressure altitudes
Why must aircraft that fly at high altitudes be pressurised?
-if air pressure is too low, humans cannot take in oxygen quick enough to meet their bodies’ needs
Upthrust
-upwards force exerted by a liquid or gas on an object partly/completely submerged in it
If the upthrust is less than the weight of the object…
….the object will sink.
How does pressure in fluids increase with depth?
-mass of liquid above the depth also increases
-force due to the mass increases
-force has increased, area remains constant, so pressure will increase
If you are higher up in the atmosphere, pressure is less, because…
…there’s less air above you pushing down.
Why is the bottom surface of an object submerged in a fluid experience greater pressure than the top surface?
-upper surface isnt as deep as the lower surface
-so there is a smaller weight of water pushing down on it
-so bottom surface experiences greater pressure as there is a greater weight of water pushing down on it
Displaced fluid
-the fluid that rises when an object is submerged in a fluid
Upthrust is equal to the weight of…
…displaced fluid.
