form 1 chapter 7

7/26/2019 Form 1 Chapter 7

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Heat



Heat as a Form of

Energy• Heat as a form of energy .Heat can make things hotand we can use heat to

do work.

• We feel hot when the Sunshines. This shows that

the Sun is a source ofheat energy and gives outheat. Most of the heat onthe Earth comes from theSun.



Other Sources of

Heat

• Apart from the Sun, there are many

other sources of heat. Heat can eproduced in many ways.

• Here are some activities to show

possile heat sources.



Heat sources Activities

• !uing or friction"

ruing two o#ectsagainst each other canproduce heat.

• !u your hands

together for sometime and then holdthem to your cheeks. $our cheeks will feel

warm, showing thatheat can e produced

y friction.

Rubbing hands can produce heat



• %urning" when ano#ect urns, it

produce a &amethat gives out

heat.

• %urn a candle or a pieceof paper and put your

hands aove it. $our handswill feel hot, showing thaturning sustances can

produce heat.

Burning substances can

produce heat



• Electricity ' whenelectric current

&ows through awire, heat isproduced.

• Switch on the electricul for some time and

place your hands near theul. $our hands can feelthe heat coming out from

the ul.

Electricity can produce heat



• Heat can also be produced by:

a. %ending metal" ending a coathanger or a wire ack and forthseveral times can produce heat inthe o#ect.

. (hemical reaction ' after mi)ingsolid sodium hydro)ide with water ina test tue, the test tue will get

warm.

c. (ollision ' when an iron nail is hit ya hammer several times, thehammer and the nail will get hot.



Bending Metal Chemical Reaction

Collision



Use of Heat in our

aily !ife• Heat is a useful form of energy."e use heat to:

a. (ooking food. *rying clothesc. %oiling waterd. +roducing steam to generate

electricitye. ood drying for reservationf. +roviding warmth



Heat and#emperature

• Heat is a form of energy. An o#ect ecomeshot when it asors heat. Heat is measuredin -oules -/.

• Temperature measures how hot or cold ano#ect is. The unit of temperature is degree(elsius (/ or 0elvin 0/. Temperature can

e measured with a thermometer.

• Heat and temperature are di1erent.

• The tale elow shows the di1erences



Heat Temperature

• A form of energy • The degree of hotness orcoldness of a body

• Heat can do work • Temperature cannot do work

• Measured in Joule (J) • Measured in degree Celsius (C)or Kelin (K)

•Transfer from a hot area to a coldarea!

"ncreases when heated anddecreases when cooled

i$erences bet%een heat andtemperature



&ommonmista'es

• 2#ects with thesame temperature

contain the sameamount of heat. The higher thetemperature of an

o#ect, the largerthe amount ofheat contained init.

#he truth

• The amount ofheat contained inan o#ect depends

ona. The type of the

material that theo#ect is made

of.. The mass or the

si3e of theo#ects, and

c. The temperature



Heat

Flo%• Heat only travels from a hotter o#ector place/ to a cooler o#ect or place/

• Heat has several interesting ways of

travelling45t travel y three ways4

a. %y conduction through solids. %y convection through li6uids or

gasesc. %y radiation through vacuum



&onduction

• The &ow of heat energy through solids such

as metals is called conduction.

• Heat energy uses molecules to help it to

get around.

• or e)ample, when a pan is heated, themolecules at the ottom of the pan start to

virate energetically. They collide with theirneighoring molecules and cause them tovirate faster. The passing of the heatenergy from one molecule to the ne)t

continues. 5n this way, heat energy travels



&onvecti

on• Heat can &ow through a li6uid or a gasecause heated parts of the li6uid gas

move.

• Warm air rising aove a heater is ane)ample.

• The &ow of heat that occurs when awarm li6uid or gas moves is known asconvection.



(adiati

on• The process where heat energy travelsthrough an empty space or a vacuum isknown as radiation.

• An e)ample of radiation is the transfer ofheat from the Sun to the Earth through

mostly empty space. Such a transfercannot occur via convection orconduction, which re6uires the movementof material from one place to another, or

the collisions of molecules within a



Heat Flo% in )atural*henomena

• Some natural phenomena occur as aresult of heat &ow.

• Warming of the earth y the Sun

a. The Sun gives solar energy everyday. *uring the day, the Earth7s

surface is warmed up and duringthe night, this energy is radiatedack into space as radiant heatenergy.



. A fraction of the solar energy that

reaches the Earth is asored, causingevaporation of water from the oceans,the lakes, the lands and plants.(onvection current carries the water

vapour up to the atmosphere to formclouds, which will form rains andthunderstorms

c. The warming of the Earth y the Suncan cause changes in the climaticconditions of the Earth and manynatural phenomena such as land ad searee3es, thunderstorms, hurricanes and



•!and and SeaBree+es

a. The une6ual heating or air over landand water will result in ree3es nearthe shores.

. *uring the day, oth land and sea areheated y the Sun. However, the landgets heated up faster than the sea.

The air aove the land surface heatsup, e)pands and rises. 5t is lighter thanthe surroundings air. To replace therising air, cooler air is drawn in from

the surface of the sea. This is the sea



#he phenomena of a seabree+e



c. At night, the land cools faster than thesea. When this happens, the air over the

warmer surface of sea heats up and rises,pulling in air from the cooler land surfaceto replace it. This is the 8and ree3e.

#he phenomena of land

bree+e



,eeping Building&ool• A uilding can e kept cool y having a

good ventilation system, so that aircirculation in the uilding is ongoing. Hotair from the uilding &ows out from thetop and cool air can &ow in from theottom.

• Most of the traditional houses are uilt

with ventilation holes at the ase of thehouse and at the top near the roof. Hot airinside the house will rise and &ow outthrough the ventilation holes at the roof.

(ool air will enter through the openings at



• 5n modern uildings, the ventilation systemis made more e1ective y installing

e)haust fans and e)tractor fans. Hot andhumid air can e sucked out and replacedwith fresh and cool air.

• Modern houses are e6uipped with fans andair conditioners to make the house cooler.Modern uildings use centrali3ed airconditioning system to cool the whole

uildings.

• 5nsulation can also help to keep a uildingcool. %uildings with loft insulation,insulating cavity walls or doule ga3ed



Heat conductors and heatinsulators

• When material allow heat to pass throughthem rapidly, they are known asconductors. All metals are good

conductors of heat compared with othermaterials.

• 2ther materials like" metals, li6uids and

gases that do not allow heat to passthrough easily are known as adconductors of heat or insulators.



E-amples of heat conductors andinsulators

Conductors Insulators

Mercury (li#uid) $lass

%iler Air

Copper &ater (li#uid)

Aluminum 'lastics

inc ubber

"ron &ood*ead Materials containing trapped air

( wool+ plastic foam+ e,pandedpolystyrene)



Uses of heat conductors

Materials/ devises Uses

Cooking utensils

"nsert image

kettle

•Cooking utensils such assaucepans+ pots and kettles areusually made of aluminum orstainless steel!

•They conduct heat #uickly andeasily to the food as thus saefuels!

Examples of the uses of heat conductors in

daily life.



Electrical appliances

Insert image

iron

•Electrical irons and hot platesare made of iron or stainlesssteel that conducts heat well.

•Heat sins that are used incomputers! dis drives andtelevisions as cooling fins are

made of aluminum

-thers

"nsert image

%oldering iron rods

•adiator coils and cooling finsbehind the refrigerator are made of

copper!

•%oldering iron rods are made ofiron with copper tips!



Uses of heat insulators

Materials/ devices Uses

&ood or plastics •Handles for cooking utensils+ kettles+

teapots+ soldering iron rods and so on!•They protect our hands from the hotsurfaces!

Cork+ asbestos sheets+ tiles To preent tabletops from being

damages by hot kitchenware orob.ects!

%awdust To coer ice blocks to slow down themelting process!

Insulators are used in many applications where

we want to minimize heat flow or heat loss.



"oolen blanet or cloth •Used to eep the bod# warm on coldda#s. The woolen blanet and the airla#er trapped inside can prevent heat

loss from the bod#.

/iberglass+ e,pandedpolystyrene foam

•0sed as insulators in the walls of icebo,es and refrigerators! Air trapped

inside acts as insulator!

insulating caity wall+double1 gla2ed glass

0sed in the buildings to preent heatfrom entering by conduction during

Aluminum 'lastics the day and preent heat loss atnight!



Benets of heat /o%s

There are many uses of heat&ow in our daily life4a. The &ow of heat through

conduction is used for

cooking and oiling.(onduction of heat is alsoapplied in electric irons,ovens and toasters.

. The &ow of heat yconvection and radiationis used to dry wet

clothes, salted 9sh and

Drying wet

clothes



c. Heat &ow through radiation gives us hotwater when we use a solar heater to asor

heat from the Sun.

d. (onvection currents can help to improveair circulation and cool our houses and

uildings. ans and air conditioners help tocool the surrounding air through convectioncurrents

Air conditioner.



e. 2ur life can e made healthier and morecomfortale with a good ventilation systemin our houses. Windows, opening ande)haust fans are things that can help to

improve the ventilation of air in a house.Warm air inside the house can e drawn outand replaced with fresh, cool air from theoutside.



Ventilation of buildings

form 1 chapter 7

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