Chapter 3
Light
Light is all around us. We see light from a lamp, from a flashlight, from a candle, and most of all from the sun. If you hold a ribbon in one hand and shake it up and down quickly, you can see short waves along the ribbon. Those waves are how we get light and heat from the sun.
WORD to KNOW
reflection: when light waves bounce back from a surface.
refraction: when light bends because it passes through a substance such as glass or water.
TRY THIS
FLASHLIGHT FUN
Flashlights can be used for making scary faces at a dark campsite, finding your way through your house at night, and…doing cool experiments!
QUESTION
How far does light shine?
WHAT YOU NEED
Medium-sized flashlight
Measuring tape
Friend
2 small mirrors
FUN FACT
Lickety-Split Light
Did you know that light travels faster than sound? Light travels at about 186,000 miles per second, or 300,000 kilometers per second. Sound only travels at about 0.2miles per second, or 340 meters per second. That's why, for example, you usually see fireworks before you hear them.
WHAT TO DO
FUN FACT
Bright History
In colonial times, people used candles to light their houses. But candles didn't put out much light by themselves. So people put mirrors behind the candles to make the light shine brighter.
WHAT'S HAPPENING
The light we see travels in rays that move very fast in a straight line. The speed of light is 186,000 miles per second. That means light travels from the Sun, which is 93,000,000 miles away, to the Earth in eight minutes!
So when you shine the flashlight at a wall, you are seeing light rays hit the wall and bounce off, or reflect. Light travels until it hits something and reflects back, even up into the night sky. And when you use mirrors, you increase the brightness of the light rays because they are bouncing back and forth between the mirrors. No part of the beam is reflecting away and making the light dimmer.
Invisible Filler
Even though you can't see it, air is more than just nothingness! Air is a gas made up of molecules that fills any container it is inside. Let's test this idea — you will need a piece of newspaper or tissue paper, an empty drinking glass or glass jar, and a deep pot (like a soup kettle) full of water. To learn the directions for this experiment, use the numbered words to fill in the blanks.
YOUR NOTES
My room
My hallway
TRY THIS
FLIP-FLOP ABC
Mirrors are tricky things. They can make us see our world very differently. They can make things appear that aren't there, and they can distort our understanding of how close or far away something is.
QUESTION
Why do things appear differently in a mirror?
WHAT YOU NEED
Medium-sized flat mirror
Sheet of paper
Pencil
WHAT TO DO
Picture of me shining my flashlight up at the stars.
POP EYE TOOT LEVEL
WORD to KNOW
palindrome: a word that reads the same forward and backward.
WHAT'S HAPPENING
A mirror is made out of a metal or glass that has been coated with a thin layer of silver or aluminum. The surface of a mirror acts as a reflector. Mirrors reflect letters that are horizontally symmetrical. This means the letters can be cut across the middle and have the same top and bottom half. An H is an example of a horizontally symmetrical letter. The letters that look backward in the mirror are ones that are not horizontally symmetrical, such as V or R. Palindromes, such as POP and EYE are words that read the same forward and backward, a different kind of symmetry. These words read just fine in a mirror.
Mega Mirror
Can you imagine a mirror that is so big there isn't a place on Earth where it would fit? Believe it or not, there is such a mirror — and you have seen it! Break the Vowel Scramble code to learn what it is and how it works.
Mirrors were originally just pools of water that, when still, produced a reflected but slightly distorted image. The most common mirrors are flat mirrors. But some mirrors are curved inward, called concave mirrors. And other mirrors curve outward, giving them a convex shape, They allow you to see a wider area than flat mirrors do. Large trucks use convex mirrors to see around their wide back ends. Parking garages place convex mirrors at their exits so that drivers can see any pedestrians walking nearby.
YOUR NOTES
What other palindromes can you think of?
What secret messages can you write in your new backward code?
Cool Quotes
Equipped with his five senses, man explores the universe around him and calls the adventure Science.
— Edwin Powell Hubble
Why did the young scientist study in a hot air balloon?
He wanted a higher education!
SCIENCE LAB: PAPER PERISCOPE
Have you ever played a game of hide-and-seek and wished you could see someone coming without being seen yourself? You can, with the help of an instrument called a periscope.
QUESTION
How can you peer around a corner or look over a wall?
WHAT YOU NEED
Empty milk carton
Tape
Ruler
Pencil
2 small square mirrors
Scissors or a box cutter
WHAT TO DO
WHAT'S HAPPENING
A periscope is an instrument that allows you to see what's going on around you even though you're hidden. It works with light rays and angles. When light reflects off the surface of the top mirror of the periscope, the light rays change direction and then reflect off of the bottom mirror. This allows you to see what is going on way above you or around a corner.
Your periscope may seem very simple, but this model was used in World War I. Soldiers would put the periscopes on their rifles so that they could duck down in the trenches and stay safe but still see what was going on around them. Submarines also use periscopes, though those models are much more powerful. A submarine sends up its periscope while the vessel is still underwater, thereby allowing it to remain hidden from view while the captain scopes out the surface of the water.
YOUR NOTES
Draw what you see with your periscope.
What a Drag!
Scientists have a name for the force that slows an object down as it moves through the air. It is called “drag.” Use the picture equations to sound out directions for an experiment. Which object shows more drag?
WORD to KNOW
gravity: the force that holds objects close to the Earth's surface. On the Moon there is no gravity, and objects just float around.
Surface Tension and Buoyancy
We live in a wet world. About 70 percent of the Earth is covered in oceans. We drink and bathe in tap water, and we use water to keep our landscapes green and healthy. Our bodies are mostly made up of water.
Water has unique properties. It holds itself together in a bubble and pushes up on boats as they float. It can be a solid ice cube; a liquid; or a gas, as water vapor.
TRY THIS
PLENTY OF PINS
Did you know that water has its own kind of skin? Bodies of water have a thin layer on the surface that is both extremely fragile and yet strong. Teeny tiny insects can flit across the top of a pond, but your boot splashes straight to the bottom of a mud puddle. What property does water have to make this “skin”?
QUESTION
How many pins can you add to a full glass of water before it overflows?
WHAT YOU NEED
Large handful of straight pins (be careful not to stick yourself)
Drinking glass
Water
WHAT TO DO
WHAT'S HAPPENING
Did you think the glass would overflow right away? Were you surprised when it didn't? The surface of the water has tension, which means the molecules are attracted to each other and exert a force on each other. That attraction pushes the molecules toward the center of the water, giving it an elastic “surface.” Surface tension explains why bubbles and raindrops hold together, and why something like a paper clip, which is denser than water, can rest flat on the surface of the water without sinking.
In this experiment, surface tension kept the water from flowing out of the glass even once you added a lot of pins.
YOUR NOTES
My guess:
Actual number of pins I used:
FUN FACT
Water Walker
There is an insect, called a water strider, that can walk on water. Its legs have tiny hairs that hold air bubbles. These allow the insect to float on top of the water.
WORD to KNOW
surface tension:the force that holds water molecules together and allows water to have a kind of skin.
Slo-Mo Rainbow
Here is a simple way to get a better look at the surface tension of a liquid. To learn how to do this experiment, use the directions to cross words out of the grid. When you are done, read the remaining words from left to right, top to bottom.
Bloop
Search the letter grid for the names of four items found in a kitchen. Use the words to fill in the blanks. Follow the directions to observe density in action!
TRY THIS
WHAT SINKS? WHAT FLOATS?
The next time you're in a swimming pool, try just being still in the water. Do you sink to the bottom or float like a cork? What about the toys you bring to the pool?
QUESTION
Which objects sink? Which ones float? Why?
WHAT YOU NEED
Kitchen sink with a drain stopper
Whole lemon
Lemon slice
Whole lime
Lime slice
Sponge
Half strand of dried spaghetti
Whole orange
Orange peel
Peeled orange
Anything else you want to try
WHAT TO DO
WORD to KNOW
volume: the measurement of the space taken up by an object.
WHAT'S HAPPENING
Pick up the orange and the lime. The orange feels heavier, right? When you placed the whole orange in the water, you probably expected it to sink, because its weight felt greater when you held it. But instead, it floated and the lime, which initially felt lighter, sank to the bottom. What's going on?
When an object is in water, the water exerts an upward force on the object. This force is called buoyancy. The amount of this force is equal to the weight of the water that is displaced, or pushed aside, by the object. If the buoyancy exerted on the object is greater than the weight of the object, it rises until it breaks the surface of the water. At this point, the buoyant force on the object is equal to its weight and it floats. If the buoyancy of an object is less than its weight, it sinks.
In this experiment, the weight of the orange displaced a volume of water that was less than the volume of the orange. Volume is a measurement of the space taken up by an object. The orange took up more space than the water it displaced, so the orange rose in the water until it reached the surface and floated. In the case of the lime, its buoyancy was less than its weight, so it sank.
As for the peeled orange, the peel increases the buoyant3 force on the orange through tiny air pockets. These pockets helped the orange stay afloat.
YOUR NOTES
Whole lemon
Lemon slice
Whole lime
Lime slice
Sponge
Spaghetti
Whole orange
Peeled orange
Other items
FUN FACT
Into the Deep
A huge submarine can submerge, also known as diving, underwater by filling special tanks with water, making it heavier. When it wants to rise, it replaces the water with air.
WORD to KNOW
elastic: able to be stretched and then returned to the original shape.
SCIENCE LAB: BUBBLE BUILDER
Whether you're blowing bubbles with soap, chewing gum, or a straw in a milk glass, these translucent, round balls are fun to play with. They grow and shrink depending on how much air you blow into them. They pop with a satisfying sound and spray, and they sometimes have rainbows in them. But did you know you can build with them?
QUESTION
Are bubbles always round?
WHAT YOU NEED
Bubble solution (see following steps)
Flat tray
Straw
BUBBLE SOLUTION
You will need:
1 gallon water
2/3 cup dishwashing liquid
1 tablespoon glycerine (you can find this at drug stores)
WHAT TO DO
WHAT'S HAPPENING
Bubble solution is essentially soap. And soap has surface tension, the force you learned about in the pin experiment. The molecules are trying to hold themselves together as tightly as possible. That's why you see a film on the surface of the soap mixture. But that film is elastic.
When you blow a bubble, you stretch the water molecules into a sphere around the air in the bubble, making the bubble round. Bubbles are usually round. But where the bubbles touch each other, their shapes change and become flat, as the molecules keep squeezing together.
YOUR NOTES
Draw a picture of your bubble construction. How high can you build it?
Magnets and Electricity
Magnets can be big or small. Tiny magnets can hold your artwork on the fridge. A compass magnet is able to point to the Earth's magnetic north pole. Magnets have a magnetic field around them. This magnetic field can create elec-tricity, using a device like a generator.
Turn on a flashlight, a toaster, or a TV. All these things use electricity. Electricity is made when positive and negative charges come into contact with each other. Nowadays, there are even some cars that can run only on electricity.
FUN FACT
Twice the Attraction
Did you know that if you break a magnet in half, you don't have two north poles or two south poles, but two brand new magnets, each with one north pole and one south pole!
TRY THIS
MAGNET MANIA
Scientists often use a problem-solving method called “trial and error” to discover the answer to a question. They form a hypothesis, otherwise known as a guess, which provides them with a possibility for an answer. And then they think of ways to test that hypothesis to see if they were correct. You are going to do an experiment built around the method of trial and error. Do you like this approach to answering a question?
QUESTION
What makes some magnets stick together and other magnets pull apart? And why do magnets stick to some things and not to others?
WHAT YOU NEED
2 hard magnets (flexible magnets don't work as well)
What is the brightest city in the world?
Electri-city!
WHAT TO DO
WHAT'S HAPPENING
A magnet has two sides to it, called poles. One side is the north pole, the other side is the south pole. The rule to remember is opposites attract. The north pole of one magnet will attract, or stick to, the south pole of another magnet. But the north pole of a magnet will repel, or push away, the north pole of another magnet. When a magnet sticks to a surface, we call that surface “magnetic.” In this experiment, you tested how magnetic various surfaces and objects are in your house.
YOUR NOTES
Bedroom door
Bathroom mirror
Metal fork
Plastic spoon
Cast iron pan
Penny
Nickel
Keys
Key rings
Kitchen faucet
Fridge
Cabinet
Oven door (make sure it isn't hot!)
(Careful: don't ever stick magnets to electronic equipment, including music players, computers, and TVs. Magnets can damage these appliances.)
FUN FACT
Pole Position
The Earth has two magnetic poles: North and South. And their magnetic pull is quite strong. Scientists believe birds rely on this magnetic field to find their way during migration.
WORD to KNOW
magnet: a mass of iron or steel or some mixture of both that can attract iron and that produces a magnetic field.
Plus and Minus
Each magnet has a north pole and a south pole, and each pole is attracted to its opposite. See if you can make a path through this maze alternating between signs that are opposites. Start on the plus (+) sign, then travel to a minus (-) sign. Rules: You can travel side to side or up and down, but not diagonally. If you come to an X, you are going the wrong way!
TRY THIS
ZAP!
Have you ever pulled on a sweater in winter and then touched a doorknob? Did you feel a jolt in your fingertips? Or have you ever touched someone's hand and felt a zap? That's static electricity.
QUESTION
What causes static electricity?
WHAT YOU NEED
Socks
Carpet
Metal doorknob
Balloon
FUN FACT
Big Bolts
One bolt of lightning can measure 3 million volts in just one second. A spark of static electricity can equal 3,000 volts.
WHAT TO DO
What happens to your hair?
WORD to KNOW
static electricity: electricity caused by rubbing two objects together.
FUN FACT
Bird on a Wire
Have you ever looked up and seen a bird sitting on a telephone wire? Ever wonder how the bird can safely sit on a wire that conducts electricity? As long as no part of the bird is touching the ground, the current passes right through the bird without hurting it. You, on the other hand, should never go near a power line.
WHAT'S HAPPENING
When you shuffle your feet on a carpet and rub the balloon on your hair, you're putting something on it called negative charges. Charges can be positive or negative. Like a magnet, two positive charges repel each other, but a positive charge and a negative charge attract each other. You build up these charges as long as you don't touch anything. Once you do, you release the charges onto another surface. And that's what causes the zap. When you then placed the balloon against the wall, the negative charges in the balloon were attracted to the positive charges on the wall. So they stuck together!
Static electricity usually isn't dangerous. It's a tiny charge. But there are times when it's a problem. At gas stations, there sometimes are signs telling drivers to touch their cars before filling their gas tanks. A driver can build up static electricity from the seat in his car and then release those charges on the gasoline hose. This can cause a fire. It is important to always be safe when using electricity.
YOUR NOTES
Draw a picture of yourself with static electricity in your hair.
SCIENCE LAB: LOCAL POWER
Many of your toys and appliances use batteries. Batteries come in all types with many different names: AA, AAA, C, D, 9-volt. But inside all those batteries are components that generate a charge. You can gather those components and put them together to make your own, small power. What name would you give your very own battery?
QUESTION
How do you make a homemade battery?
WHAT YOU NEED
Potato Battery
Potato
Penny
Piece of aluminum foil
Lemon Battery
Lemon
Galvanized steel nail
Copper nail
Volta's Pile
6 pennies
6 paper towel circles
Plate
6 circles of aluminum foil
Salt water (1 teaspoon salt dissolved in 6 ounces of water)
Other Items
Knife
Voltmeter (can be purchased at local electronics store)
WHAT TO DO
Potato Battery
Lemon Battery
Volta's Pile
WHAT'S HAPPENING
In 1800, a man named Alessandro Volta discovered that if he put copper and zinc together with a wet paper in between, he could generate a certain amount of voltage. That construction is known as Volta's pile, and it generated about 1 volt, named after him.
A battery is made up of cells similar to Volta's pile. And each cell contains one half-cell with electrolyte and a positive electrode and a second half-cell with electrolyte and a negative electrode. The electrolyte helps move the charge from the negative and positive electrodes through the battery.
In your batteries, the copper and zinc are the electrodes, and the lemon, the potato, and the salt water solution are all acting as electrolytes. You use a voltmeter to measure the voltage and current produced by each battery.
YOUR NOTES
Potato Battery Voltage:
Lemon Battery Voltage:
Volta's Pile Voltage:
Which battery generates the most voltage?
FUN FACT
Eel-ectric!
The electric eel causes quite a shock. It can produce 600 volts of electricity — enough to kill fish for a meal and scare off predators!
