Chapter 11 Flashcards
what is pressure?
the result of when objects exert force on eachother
how to increase pressure? 2
decrease SA
increase force
how to decrease pressure? 2
increase SA
decrease force
what are the units for pressure?
N/m^2 which is equal to 1 Pascal (Pa)
equation for pressure?
force/area
what happens to the pressure of a liquid as depth increases?
it increases
what does pressure in a liquid depend on?
depth and density
where is the force of a liquid exerted?
on the surface in contact with the liquid
why is the pressure of a liquid higher when the density is higher?
there are more particles in a given area so there are more particles able to collide with the surface in contact, meaning pressure is higher
why is the pressure of a liquid higher with increased depth?
there are more particles above that point so there is an increased weight, meaning more pressure
what is the same in a liquid?
the pressure on a straight horizontal line
what does the pressure at the bottom of a column of liquid depend on?
the height of the column, gravitational field strength and density
how to calculate pressure at a certain depth using the column of water above it
pressure = height of column x density x gravitational field strength
unit for pressure of a liquid column
Pa (1Pa -= 1N/m^2)
what is the earth’s atmosphere?
a layer of air around the earth
what pressure does the earth’s atmosphere exert at sea level?
100 kPa
what is atmospheric pressure caused by?
air molecules colliding with surfaces
why does the atmospheric pressure decrease with height?
the atmosphere gets less dense so there are less air molecules pressing down on that surface
there are fewer air molecules above that point, so less weight = less pressure
give two examples where atmospheric pressure is used
suction cups
sucking up a straw
how does suction work?
when you push the cup to the wall, there is no air inside it so no air to push it away from the wall
atmospheric pressure acts on the outside of the cup but not the inside, keeping it up
how does sucking up a straw work?
when you suck, you pull all the air out of the straw
the atmospheric pressure acts on the water and pushes it up the straw because there is no resistance (you have sucked all the air that would push water out of the straw out)
what happens to the atmospheric pressure at high altitude?
it decreases
atmospheric pressure at sea level
100 kPa
atmospheric pressure at the top of mount everest
30 kPa
what is an atmosphere?
a thin layer of air surrounding the earth
equation for pressure at sea level
pressure = height x density x gravitational field strength
what is upthrust?
the pressure a liquid exerts on an object in it
when will an object float?
when its weight = upthrust
what does whether n object will float or not depend on?
density
how do submarines use upthrust?
tanks filled with water means weight is more than upthrust so they sink
tanks filled with compressed air to rise, meaning the submarine weighs less then upthrust
why does an object sink?
if it is more dense than water, it means that its weight is more than the volume of liquid displaced. This means the weight of the object is greater than the force of upthrust
why does an object float?
it is less dense than water
it weight is less than the volume of water it displaces
the weight of the object is less than the force of upthrust
what is upthrust?
the resultant force of the pressure of the water on the top of an object and the pressure of water on the bottom of an object
what is upthrust equal to?
the volume of water that is displaced by an object
