density / pressure Flashcards
mass is measured using
an electronic balance
- zero it
- use on a level surface
measure volume
regular = cross section area x length
irregular - displacement method
- put in eureka can and measure displacement (at eye level, bottom of meniscus on level surface)
pressure in solids
force spreading out over a large area reduces pressure
mass - weigh on electronic balance
convert to force using W = mg
find area
calculate pressure
how to measure diameter
use callipers to find diameter
or ruler and set squares
repeat in diff places and average
how to measure irregular shape
on a squared piece of paper draw shape and count squares
pressure in liquids
increases with depth as there is a greater weight of water above you
this is why dams are thicker at bottom
pressure is same at all points of the same depth (depends on depth not shape of container)
liquid pressure experiment
fill cylinder and block holes then release and draw diagram of path water takes out holes
ml > cm^3
1 ml = 1 cm^3
why not accurate
parallax error
not on flat surface
not read at meniscus
set to zero
most precise
smallest volume and increments (smallest resolution)
how to find density
- calculate mass on electronic balance
- calculate volume
- use p = m/v
- repeat and average
what to control - density
temp
as temp changes so does density
pressure measured in
N/m^2 / pascals (Pa)
or N/cm^2
why balloon increases in size (bell jar)
- gas pressure inside the balloon is greater than outside (no air outside)
- hence the pressure difference causes balloon to expand
why ballooons move together when air blown between them
- pressure inbetween is lower than pressure either side
- because faster air has less pressure
- pressure difference means they move together
change in pressure related to speed
faster air = less pressure
why do ears pop in plane/ deep water
to equalise pressure between the inside of your head and surroundings
(pressure differences cause expansion or contraction)
atmospheric pressure
100 kPa
pressure to area graph
curve (reciprocal)
boyles law
at constant temp volume is inversely proportional to pressure
pressure is what to volume
pressure is inversely proportional to volume
kinetic theory
- gas molecules collide with container walls
- exerts force on walls
- total force from all collisions acts on inside area of container
- since p= F/A pressure is produced
how kinetic theory explains boyles law (volume and pressure)
- when volume decreases
- molecules don’t have as far to travel before hitting container walls
- so they collide more frequently and pressure increases
ideal gases vs real gases
stay as a gas all the way to absolute zero
real gases - condense to a liquid before this point
absolute zero
-275 °C
0°K (kelvin)
gas pressure relation to temp in kelvin
gas pressure is proportional to temp in kelvin assuming mass and volume are constant
what needs to be constant in pressure
mass
volume
how kinetic theory explains pressure law (pressure and temp)
- as gas is heated molecules gain KE
- so move faster and collide with walls of container harder and more frequently
- so pressure increases
