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what physical properties do materials have (how do we determine volume…
what physical properties do materials have
materials can be classified into 5 groups based on common physical properties
physical property is one that can be observed without changing substance of object
physical properties
strength
ability to support heavy load without breaking or tearing
steel: can withstand heavy loads for long period of time: used to make bridges
hardness
ability to scratch another material
material will scratch another material softer than itself but not one harder than it
diamond is hardest material in world: diamond blades can cut stones, metals and other hard materials
flexibility
ability to bend without breaking and return to original shape
nylon: when used to make fishing rod, allows fisherman to pull fish in without breaking rod
electrical conductivity
measure of how easily electricity passess through
copper: used for electrical wiring and is good conductor of electricity
heat (or thermal) conductivity
measure of how easily heat passes through
materials that allow heat to pass through easily are called heat conductors
metal: god heat conductor: used to make cooking pots as heat passes through to food quickly
melting point
temperature at which changes state from solid to liquid
gold melts at 1064 degrees celcius
boiling point
refers to temperature at which changes state from liquid to gas
water boils at 100 degrees
density
metals have highest density
pg 42
texture
how material feels when touched: hard, smooth, soft or rough
glass feels smooth while fibres feel soft
lustre
attractive shiny appearance of material
many metals have high lustre as they are shiny
transparency
can we see through it?
glass and some plastics are transparent
metals and ceramics are opaque
cannot see through opaque materials
rotting
materials rot/decompose when breaken down due to fungi are usually buried in ground
materials made from living matter such as natural fibres(cotton, wool), rot
other 4 kinds of materials do not rot
materials that rot->called biodegradable
corrosion: slow destruction or wearing away of material due to action of substances such as air, water and acids
most metals corrode
rusting of iron due to action of substances in environment
other materials eg, plastic and glass are largely resistent to corrosion
pg 43
what is density
describes how mass of substance changes with volume
some objects may have same volume but one of them might be heavier
this difference is due to masses
they have different masses as they are made of materials with different densities
mass of object per unit volume
mass/volume
how do we measure length
length is physical quantity for us to calculate area and volume
pg 44
length is physical quantity needed for us to calculate area and volume
SI unit of length id metre
short lengths are measured in cm or mm
long distances are measured in km
what instruments do we use to measure length
metre rule
to measure short lengths, use ruler, half-metre ruler or metre ruler
measure length in cm
when using it, must place eyes vertically (90degrees) above it
allows us to obtain correct reading
placing our eye in wrong position will lead to paralax error which will give inaccurate reading
measuring tape
measure longer lengths and lengths of curved surfaces
this and meter rule have marks dividing them into cm .and mm which is smallest division
metre rule and this are accurate to 1mm or 0.1 cm
pg 45
vernier callipers
measure internal and external lengths of objects very accurately
accurate to 0.1 mm/ 0.01 cm
pg 46
how do we determine volume
amount of space substance occupies
si UNIT OF VOULUME IS CUBIC METRE m3(tiny)
for smaller volumes, can use com3 instead
pg 47
measure volumes of liquids
measuring cylinder
cubic centimeters
liquid surface is a little curved
curved shape called meniscus
pg 48
how do we measure mass
mass=amount of matter
all matter has mass
mass=amount of matter
SI unit of mass is kg
maller masses measured in g and mg
large masses measured in tonnes
pg 49
what instruments do we use to measure it
(electronic) balance
pg 50
zero error
electronic balance has 0 button while double beam balance has zero-adjustment knob
they endure that initial balance reading is 0
how do we determine density
SI unit for density is kg/m3. however, most common unit of density is g/cm3
objects made of same substance has same density
pg 51
pg 52
why do objects float or sink
object floats if its density is less than that of medium it is in
thus, beach ball filled with air(object) which is less dense than water (medium) will float
pg 53
applications of floating and sinking
pg 54