HEAT

Metal heated in a furnace shows that it is hot by glowing red and sending out sparks – but there is also some heat in ice and snow. Heat is the energy of movement, or kinetic energy, stored inside every object, hot and cold alike. Heat energy makes the particles (atoms and molecules) inside the object move about. TEMPERATURE is how hot or cold an object is, depending on its heat energy. Temperature is measured with a THERMOMETER.

MOLTEN METAL

When iron is heated in a furnace, it glows red-hot and then melts at a temperature of 1,535°C (2,795°F). At this temperature, its particles move about with lots of kinetic energy. At higher temperatures they move even faster, and the iron in the furnace starts bubbling.

ICEBERG

Ice is cold, but it still contains some heat energy. An iceberg is made up of particles of water, held in a rigid crystal structure. They still vibrate slightly. If the iceberg cooled down so that its particles stopped moving altogether, it would be at the lowest possible temperature that can ever, in theory, be reached. This is absolute zero.

TEMPERATURE

Temperature is a measure of how hot or cold something is. Things that have high temperature are hotter than things that have lower temperature, because they have more heat energy inside them. Any object can transfer heat energy to a colder object. As it does so, it cools down and its temperature falls. The colder object warms up and its temperature rises.

TEMPERATURE SCALES

Temperature is measured in degrees Celsius or Fahrenheit (°C or °F) or on the absolute temperature scale, in units called Kelvins (K). The Celsius (also called Centigrade) scale runs from freezing point (0°C) to boiling point (100°C).

THERMOMETER

This is a device that measures how hot or cold something is on a temperature scale. When things get hotter, their heat energy makes them expand or get bigger. This is how a thermometer measures temperature. As the liquid inside expands, it creeps up a tube, which is marked with a scale and numbers that show the temperature.

MERCURY IN BULB

The thermometer contains a small amount of liquid mercury in a glass bulb at the bottom. To take someone’s temperature, the glass bulb is placed inside their mouth. As the mercury is warmed by the person’s body, it expands up the tube, and climbs the temperature scale. A kink in the tube stops the mercury falling back too quickly, so the temperature can be read and recorded.

THERMOSTAT

A thermostat switches an air-conditioning unit on and off to keep a room at a constant temperature. As the room heats up, the brass strip inside the thermostat expands more than the iron strip attached to it. The strip bends inwards, completes an electrical circuit, and switches on the air-conditioning unit.

Copyright © 2007 Dorling Kindersley

stay connected

Sign up for our free email newsletters and receive the latest advice and information on all things parenting.

Enter your email address to sign up or manage your account.

Facebook icon Twitter icon Follow Us on Pinterest

editor’s picks

highlights

3 Fun Thanksgiving Games for Kids
Looking for some great Thanksgiving games to play with your kids? Print our free Pin the Feathers on the Turkey game, Pin the Hat on the Pilgrim game, and Thanksgiving Parade Bingo game for loads of laughs this Turkey Day!

Kindergarten Readiness App Wins Gold
Our Kindergarten Readiness app won the Gold Award of Excellence in the educational category at the 2014 Communicator Awards. This valuable checklist comes with games and activities to help your child practice the essential skills she needs for kindergarten. Download the Kindergarten Readiness app today!

Top Family Movies in Theaters for the Holidays
Taking the kids to the movies is a special family treat for the holidays! Don't miss 2014's best family films in theaters from Thanksgiving through Christmas.

Find Today's Newest & Best Children's Books!
Looking for newly released books for your child? Try our new Book Finder tool to search for new books by age, type, and theme, and create reading lists for kids!