# physics topic 3

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## density of materials

comapctness of a substance-mass per unit volume

DENSITY=MASS DIVIDED BY VOLUME

a dense materila has partcles packed together

less dense partcles are more spread out

IF YOU COMPRESS PARTICLES MOVE CLOSER TOGETHER BECOMING MORE DENSE

VOLUME WOULD DECREASE BYT MASS WOULDNT CHANGE

3 STATES OF MATTER

SOLIDS,LIQUIDS, AND GASES

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## SOLIDS LIQUIDS AND GASES

SOLIDS STRONG FORCES OF ATTRACTION PARTCLE CLOSE TOGETHER FIXED REGULAR ARRANGEMENTSO ONLY VIBRATE

DENSITY HIGHEST THIS STATE AS PARTCLES CLOSESTS TOGETHER

LIQUIDS WEAKER FORCES OF ATTRTACTION PARTCLES CLOSE TOEGETHER BUT MOVE AND FORM IRREGULAR ARRANGEMENTSMORE ENERGY

LESS DENSE THAN SOLIDS

GASES ALMOST NO FORCES OF ATTRTACTION BETWEEN PARTCLES HAVE MORE ENERGGY AND TRAVEL HIGH SPEEDS RANDOM DIRECTIONS

LESS DENSE THAN  LIQUIDS AND SOLIDS

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## how to measure density-practical

to find density of solid object-

use a BALANCE to meausre mass

is regular solid-measure length widht and height and calculate volume

irregular solid SUBMERGE IT IN EUREKA CAN FILLED WITH WATER-water displced by object place in measuring cylinder

record volume of water there

put mass and volume in formula to fimnd out density

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## practical

to find density of liquid-

place measuring cylinder on a balance and zero the balance

pour 10ml of liquid in and record liquids mass

pour another 10ml and repeat untill full-record mass and total volume each time

for each meausrement use formula find density

take an average

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## internal energy and changes of state

internal energy is TOTAL ENERGY STPRED BY PARTCLES THAT MAKE UP A SYSTEM

PARTCLES VIBRATE OR MOVE AROUND so  have energy in kinetioc energy stores

energy is stored  in partcles

when heating a system the energy is transfered to its particles -so gain energy in kinetic energy stores causing them to move faster- INCREASING INTERNAL ENERGY

LEADING TO CHANGE IN TEMP OR STATE

SIZE OF CHANGGE DEPENDS ON MASS AND ENERGY INPUT

THE ENERGY BREAKS BONDS  HOLDING PARTCLES TOGETHER

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## conservation of mass

changes of state-

SOLIDS-

MELTING-liquid

SUBLIMATION-gas

LIQUIDS-

FREEZING-solids

BOILING AND EVAPORATING-GAS

GAS-

CONDENSING-liquid

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## changes of state

physical chnage not chemical MEANS DONT END UP WITH NEW SUBSTANCE

REVERSING A CH AGE IN STATE SUBSTANCE WILL RETURN TO ORIGINAL STATE

MASS IS CONSERVED AS NUMBER OF PARTCILES DONT CHNAGE ONLY ARRANGEMENT OF PARTCLES

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## SPECIFIC LATENT HEAT

CHANGING STATE REQUIRES ENERGY

WHEN MELTING OR BOILING A SUBSTANCE YOU ARE OUTTING ENERGY IN WHICH IS INCREASINGG THE INTERNAL ENERGY

ENERGY IS USED FOR BREAKING INTERMOLECULAR BONDS NIOT RAISING TEMPERTAURE

WHEN CONDENSING OR FREEZING BONDS ARE FORMINGG BETWEEN PARTCLES WHICH RELEASES ENERGY

INTERNAL ENERGY THEREFORE DECREASES BUT TEMP DOESNT GO DOWN UNTIILL ALL SUBSTANCE GOES TO LOIQUID

THE ENERGY NEEDED CHANGE STATE OF SUBSTANCE IS LATENT HEAT

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## specific latent heat

energy needs to chnage state of 1kg mass

from one state to another without changing tempertaure

when coolingg slh is the energy released

SPECIFIC LATENT HEAT OF FUSION IS FOR CHNAGE BETWEEN SOLIDS AND LIQUIDS-MELTINGG AND FREEZING-

SPECIFIC HEAT OF EVAPORISATION IS SLH FOR CHANGING A LIQUID AND GAS-EVAPORATING CONDENSING OR BOILING

FORMULA

ENERGY=MASSXSLH

energgy joules, mass kg and slh j/kg

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## particle motion in gases

average energy in kinetic stores reaktes to tempertaure

GAS-

particles  constantly moving around random directions and speeds

if increase temp, transfer energy into kinetic energy stpres of its partcles

higher temp higher average energy

COLLIDING AS PARTCLES CREATES PRESSURE -exert a force

in a sealed conatiner, outward gas pressure is total force exerted by particles on unit area of container

increase un net force if increase in temperature

IF TEMP CONSTANT AND INCREASE THE VOLUME OF GAS PARTCLES GET MORE SPREDA OUT HIT WALLS LESS PRESSURE DECREASES

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## pressure

pressure and volume are inversely proportional-as VOLUME GOES UP PRESSURE GOES DOWN

PRESSURE-PASCALS-xVOLUME=CONSTANT

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## volume

change is presuure cause change in volume

because pressure of partcles cause net oitwards force on container at right angles

also presuure on outside of conatiner due to pressure of gas around it

if a conatiner can easily chnage its size then then chmahe in pressure will casue container to compress of expand

EXAMPLE HELIUM BALLOON

WHEN RELEASED ATMOSPHERIC PRESSURE DECREAZES WITH HEIGHT SO PRESSURE OUTISDE BALLOO DECREASES CAUSING BALLOON TO EXPAND UNTILL PRESSURE INSIDE DROPS TO SAME AS OUTSIDE

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## doing work on a gas

is you transfer energy by applying a force your doing work

this increases internal energy which increases temp

EXAMPLE-BIKE PUMP

GAS APPLIES PRESSURE TO PLUNGER OF PUMP AND EXERTS A FORCE ON IT

WORK HAS TO BE DONE AGAINST THIS FORCE TO PUSH DOWN PLUNGE

THIS TRANSFERS ENERGY TO KINETIC ENERGY STORES OF GAS PARTICLES INCREASING TEMP

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