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
Ship upthrust example - increasing weight
-load increases = more weight
-displaces more = upthrust increases
if upthrust = weight of an object
floats
when do objects sink
-when an object displaces max amount of water as water molecules can no longer move and upthrust cannot support its weight
if upthrust is less than weight of an object
sinks
size of upthrust
= weight of water displaced
why will a more dense object sink
-weight is greater than water displaced
-weight > upthrust
less dense objects will
float
-displaces less than its weight
-upthrust is enough
weight of object is equal to 2 factors
-water displaced
-upthrust
