P11 - Pressure Flashcards
pressure
-caused when object exert forces on each other
-when a fluid exerts a force on an object that it is in contact with
fluid
-either liquid or gas
pressure depends on
-area of contact
-size of force
pressure unit
force per unit area
pascal = n/m^2
formula for pressure
p = f/a
force must be
90 degrees to surface
liquid pressure and depth
-increases with depth
water jets in water bottle
-deepest hole = most pressure
pressure and density
-higher density = higher pressure in liquids
pressure of liquid formula
pressure = h x density x gravity
Earths atmosphere pressure
100kPa
atmospheric pressure
-due to air molecules colliding with surfaces
-each impact exerts a small force on a surface
-number of molecules that collide each second is large
density of atmosphere (altitude)
-decreases as height increases
reason for lower air density at higher altitudes
-weight of air molecules above is less
-fewer molecules per cubic metre
-fewer impacts per second
pressure at high altitudes
-weight of air above exerts less pressure on air below
-lower pressure
Rubber suction cap example
-atmospheric pressure acts on outside of cap only
-forces cap onto wall = forces air out inside
-pressure diff keeps cap onto wall
o2 concentration at high altitudes
decreases
force from pressure diff formula
pressure difference x area
upthrust
upward force on an object due to fluid
-caused by pressure of fluid
upthrust in water
water exerts upward force on body it is in contact with
adding an object into a body of water
-water level rises
-displaces some water molecules
the more the object is lowered
more volume of water is displaced = larger upthrust
a fully immersed object’s volume
total water displaced = volume of object
upthrust formula of an object that is fully immersed
resultant = pressure below object - pressure above object
