05 Pressure And Density Flashcards
How to calculate density of regularly shaped objects
- density =mass/volume
- measure mass w/ balance
- measure dimensions of object using ruler
- repeat and take avg
How to calculate density of irregular object
- density =mass/volume
- measure mass w/ balance
- add object in water (measuring cylinder of known volume OR displacement eurika can)
- measure volume of displaced water using measuring cylinder (bottom of minescus)
- repeat and take avg
Calculating density of liquid
- density = mass/volume
- measure mass of empty measuring cylinder w/ balance
- measure mass of full measuring cylinder using balance
- mass of liquid = full cylinder - empty cylinder
- measure volume using measuring cylinder from bottom of meniscus
- repeat and take avg
High pressure good for
Cutting
Low pressure stops
Sinking
How pressure at a point in gas/liquid/rest acts equally in all directions
- when collide with something, particles in gas/liquid exert force
- when all of forced are added due to collisions with surface, resultant force is equal in all directions
- so pressure is equal in all directions
Arrangement and motion of particles in a solid
Strong forces of attraction between particles
Regular arrangement
Closely packed together
Vibrate about fixed positions
- why solids keep shape and can’t be compressed
Arrangement and motion of particles in a liquids
Forces between particles not strong enough to hold in a place so they move past each other
Irregular arrangement
Particles closely packed together
- this is why liquids can flow and take shape of their container and can’t be compressed
Arrangement and motion of particles in a gases
Weak forces between particles
Irregular arrangement
Particles spreads out and moves randomly
- this is why gases can flow and take shape of container and also can’t be compressed
When heat is applied to object what happens to particles
When heat is applied the particles in object gain KE
Particles in object vibrate more quickly
If energy energy is supplied the object can change in state
Solid to liquid (melting)
Solid is heated and some intermolecular bonds are broken
Liquid to gas (boiling)
Liquid is heated and the remaining intermolecular bonds are broken
Evaporation
Gas particles escape from liquid
Occurs at temperatures lower than BP
Particles near surface of liquid carry most KE
When particles evaporate from liquid a cooling effect occurs
What happens when u heat a substance
Temperature rises
- but temperature doesn’t change until it has changed state
- because energy is being used to break bonds between particles
Practical: obtain temperature time graph to show constant temp during change of state
- fill beaker with ice and add thermometer
- gentle heat ice cubes w/ Bunsen burner
- record temp at regular intervals and when ice begins to melt
- eventually all ice melts to form water
- continue heating until water boils and record the temp
- plot results on temp time graph
How pressure at point acts equally in all directions
- when collided, particles exert force
- when all forces are added resultant is equal is all directions
- pressure equal in all directions
Specific heat capacity
Energy required to raise the temp of 1Kg of substance by 1 degree Celsius
Practical: investigate SHC of material using water and some solids
- use c = E/m x change in t
- measure energy using joulemeter
- measure time w/ stopwatch
- measure mass with balance
- measure change in temp (final-initial) using thermometer
- repeat and take avg
Ideal gas molecules
- constant state of random motion
- no forces of attraction between particles Irregular arrangement
Why do ideal gas molecules not loose energy during collisions
Collisions are elastic
Idea gal molecules - higher temp
Faster molecules (more KE)
Brownian motion
- particles floating in liquids and gases move randomly
- because they are hit by other moving particles in fluid
- exerts resultant force
Molecules in gas on walls of container
When particles of gas collide with something, particles in gas exert a force on it
In a sealed container, gas particles hit walls of container creating an outward force
- pressure created
For a fixed mass of gas at constant temp, the product of pressure and volume is
Constant
Volume doubles
Pressure halves
Why is the product of pressure and volume constant
Smaller space molecules have to move -> more frequent collisions with surface of container
Pressure doubles
Volume halves
Objects at same temperature have same
Average kinetic energy per particles
(Higher temp higher KE)
When kinetic energy = 0
Temp = -273 = 0 kelvin
Kelvin temperature (K) =
Celsius temperature + 273
Pressure and kelvin temp are
Proportional at constant volume
As temp increases
- KE of particle increases
- particles speed increases
- number of collisions + force of collisions increase
- pressure increases
Kelvin temp doubles
Pressure doubles
