S oundsThat Se e in theDark Hel-l-o-o-o-o-o A boy hears the echo coming from the hills Echo talk to me he calls to me repeats the echo to me to me to me What is an echo It’s a sound you make that bounces back to you from What if nothing stops the sound waves Then they just get smaller and smaller Or they are absorbed by soft things such as carpets draperies or large pieces of furniture That’s why we don’t usually hear echoes in the house hills or other surfaces But how can a sound bounce It’s not a ball Actually sound is a wave in the air If you could see air the way you see water you’d see the waves that sounds make Sound waves bounce only if they hit something big and solid like the side of a hill or the walls of a cave It is the D I D YO U K N O W i s s a i d t h a t a d u c k s q u a c k only sound that doesn’t echo If you long happen to have a duck and a l w a y y o u c o u l d t e s t t h i s t h e o r y hal yourself 10
ECHOES Did you know that echoes can help some animals see in the dark In pitch-dark caves bats fly easily never bumping into anything and even catching tiny insects in the air As they fly they make tiny whistlelike sounds These sounds bounce back to them The direction of the echo and the time it takes for it to return tell the bats exactly where things are as they fly Human beings have learned to harness the power of echoes for navigation too Submarines traveling underwater use sonar to bounce sounds off of solid objects so that they can tell where those objects are located sort of like undersea bats LEARN MORE READ THESE ARTICLES ENERGY RAINBOWS WAVES S EA R C H LIG H T What animal uses sound to see Dolphins do the same thing underwater Answer Bats use echoes to tell what is around them in the dark 11
o f Life The P o w e Without energy in our bodies we wouldn’t be able to do anything We couldn’t walk talk or even play Energy is usable power And all energy is related to some kind of motion r All living things need energy no matter what they do Plants get their energy from sunlight This energy is stored in different chemicals inside the plant This whole process is called photosynthesis Animals that eat plants take the energy stored in the plants The energy is then stored in chemicals inside the animals as food energy The same happens when animals eat other animals Plants and animals use energy every day as they grow and do the work of being a plant or an animal So plants have to keep absorbing sunlight and animals have to keep eating plants or other animals It isn’t only living things that have energy A dead tree has hidden energy When we burn its wood it gives off warmth or heat energy The Sun too makes heat energy as it constantly burns The Sun gives off not just heat but also light as light energy A battery in a flashlight makes it shine generating light energy But if we put the same battery in a radio we get music A battery’s energy is known as electrical energy And in a toy car that electrical energy produces movement or kinetic energy If we couldn’t use heat light or electrical energy we couldn’t drive cars or cook food We wouldn’t have light at nighttime Basically we’d have to use the energy of our own bodies And that would mean eating a lot more and doing a lot less LEARN MORE READ THESE ARTICLES MARIE CURIE LEAVES THUNDER AND LIGHTNING 12
ENERGY in D I D YO U K N O W is measured Energy from food calories A grownup needs to take a b o u t 2 0 0 0 2 5 0 0 c a l o r i e s a d a y in a major race eat three to five times that much and they sti Bicycl s o m e t i m e s r u n o u t o f e n e r g y ists in l l S EA R C H LIG H T These sentences are all mixed up See if you can fix them Heat energy comes from the things people or animals eat Food energy comes from things that burn Food energy comes from things people or animals eat Answer Heat energy comes from things that burn 13
