5b: Density and pressure

relationship between density, mass and volume

density = mass / volume

pressure (solids)

force per unit area

relationship between pressure, force and area

pressure = force / area

unit for pressure

pascals

3 states of matter - most dense to least dense

• solid

• liquid

• gas

1 kg to g

1000

1 m^3 to cm^3

1000000

cm^3 to m^3

10^6

fluid

liquid or gas

what happens to an object when it's immersed in a fluid

the fluid exerts pressure evenly across the whole surface in all directions and squeezes the object so force is created against surfaces and act at right angles to it

relationship for pressure difference

height x density x gravitational field strength

formula for pressure in liquids

pressure difference

does pressure in liquids change with depth

yes

where is pressure highest in a liquid container

at the lowest point it has the highest intensity

what happens to force in deep water

force increases as depth increases

determining density - apparatus

• regularly and irregularly shaped objects

• suitable liquid

• 30 cm ruler

• vernier caliper

• micrometer

• digital balance

• displacement can (eureka)

• measuring cylinders

determining density - regularly shaped objects (variables)

independent variable: type of shape/volume
dependent variable: mass

determining density - regularly shaped objects (method)

• weight the object on a digital balance

• measure its dimensions

• repeat and take average before calculating density

determining density - regularly shaped objects (volume of sphere)

4/3π r^3

determining density - regularly shaped objects (volume of cube)

lwh

determining density - regularly shaped objects (volume of cylinder)

π r^2 l

determining density - irregularly shaped objects (variables)

independent variable: different irregular shapes/mass
dependent variable: volume of displaced water

determining density - irregularly shaped objects (method)

• weight the object on a digital balance

• place an empty measuring cylinder below the eureka can's spout

• fill eureka can with water

• lower object into eureka can

• measure volume of displaced water in cylinder

• repeat and take average

determining density - irregularly shaped objects (analysis)

volume of water displaced = volume of object

determining density - liquids (variables)

independent variable: volume of water addedd
dependent variable: mass of cylinder

determining density - liquids (method)

• weigh an empty measuring cylinder on a balance

• fill the cylinder with the liquid and note the volume and new reading on the digital balance

• repeat and take average

determining density - liquids (analysis)

mass of liquid = mass of cylinder with water – mass of cylinder

determining density - systematic errors

ensure balance is set to 0

determining density - random errors

• take repeated readings

• place irregular object in displacement can carefully

determining density - safety

• glassware

• electric shock if water is poured into measuring cylinder while on balance

• react to spills