Childrens Illustrated Encyclopedia

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Atoms and molecules

Earth

Engines

Science

Stars

Sun

Volcanoes

Sweating and Shivering

Your body usually has a steady temperature

of 98.6°F (37°C). It automatically keeps

you from getting too hot or

too cold. Sweating cools

you down if you get too

hot. Shivering helps

to warm you up when

you get too cold. Hairs

on your skin stand up when

your body gets cold and

help to trap a layer of air

around the skin, which

stops heat loss.

Drops of sweat

evaporate, which

cools the skin.

FAHrEnHEIt

temperatures marked with

an “F” are recorded using the

Fahrenheit scale of temperature.

In the Fahrenheit scale, water

freezes at 32°F and boils at 212°F.

A few countries, including

the United States, use

the Fahrenheit scale.

Aluminum

melts,

1,220°F

(660°C)

Water

boils,

212°F

(100°C)

Normal

body

temperature,

98.6°F

(37°C)

Water

freezes,

32°F (0°C)

Oxygen

becomes

liquid,

-360°F

(-218°C)

Absolute

zero,

-460°F

(-273°C)

tHErmomEtEr

A thermometer is an instrument that measures temperature. A digital

thermometer has a display that shows the temperature in numbers.

Glass thermometers contain a thin column of mercury (a liquid

metal) or colored alcohol that expands and

rises in the thermometer as the

temperature increases.

Digital display

accurately records

temperature

within one-tenth

of a degree.

AbSolUtE zEro

the lowest temperature of

all is called absolute zero.

At absolute zero, -460°F

(-273°C), molecules stop

moving. Scientists have

cooled substances almost

to absolute zero, but the

exact temperature can

never be reached.

Column of

colored

alcohol

Level of

column

indicates

temperature

against scale.

rEFrIGErAtor

When liquids evaporate (change

into a gas), they take heat from

their surroundings. In a

refrigerator, a liquid circulates,

going through a cycle of

evaporation and condensation

(changing back into a liquid

again). As the liquid evaporates,

it takes heat from the food in

the refrigerator.

CElSIUS

temperatures

marked with a “C” are

recorded in the Celsius

(also called Centigrade)

scale of temperature. In this scale,

water freezes at 0°C and boils at

100°C. Scientists and most countries

of the world use the Celsius scale.

Shivering makes

muscles move and

produce heat.

tEmpErAtUrE

temperature is a measure of how hot an object

is. A hot object has a higher temperature than

a cold object. When objects are extremely

cold, they have negative

temperatures: a minus

sign indicates how many

degrees the temperature

is below zero on the

temperature scale.

expanSion and contraction

most things expand (get slightly larger) when they get hot.

they contract (shrink) again when they cool. this happens

because the molecules inside an object make larger, more rapid

vibrations as the object heats up. the molecules therefore take

up more space, causing the object to expand. the Golden Gate

bridge in San Francisco expands by up to 3 ft (0.9 m) in the

summer months because of the hotter weather.

Heat is

taken from

air inside the

refrigerator.

Electric pump

forces liquid around pipes

inside refrigerator.

Vapor changes

back to liquid in

condenser, and

continues its

cycle around the

refrigerator.

Surrounding

cool air outside

the refrigerator

removes heat.

When vapor

condenses back

into a liquid, it gives

out heat to the air

around the

condenser.

Liquid changes to

vapor in evaporator

by taking heat from

inside the refrigerator

and cooling it.

Heat

Center of

the sun,

about

27 million°F

(15 million°C)

Center

of Earth,

about

8,100°F

(4,500°C)

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