UNIT 01
ENERGY BASICS

WHAT IS ENERGY? You’ve probably heard someone describe another person as “high energy,” or perhaps you’ve seen a news story about clean energy. Energy is all around us: it’s a part of everything we do and everything we see. It can be described as the ability to do work or make a change. It helps people move and plants grow. It powers machines and technology. We observe energy all around us in the forms of heat, light, sound, and motion.

The labs in this unit will help you recognize that energy is always present. By the end of Unit 1, you’ll be able to observe many of the things energy can do. You will explore how heat moves in solids, liquids, and gases. You’ll observe light and how it travels. You’ll test how objects move with different amounts of energy and friction. You’ll make sound travel through different mediums. These are all examples of work or change.

Let’s get to work!

Observing convection currents in Lab 1.

CONVECTION CURRENT IN A CUP

Why does the deep end of a pool always feel so much colder? Why does cold coffee creamer sink to the bottom of a cup of hot coffee, so that it needs to be stirred? This lab will explore how heat, or thermal energy, moves through fluids.

TIME:
15 minutes

PERSON POWER:
No Sweat!

MESS ALERT!
Be cautious with food coloring; it can stain fabrics, furnishings, and your skin. Use a plastic tablecloth or newspaper under the cups, just in case!

SAFETY IS KEY:
Be cautious handling hot water. The hot water needed for this activity should be just under boiling, approximately 185–200˚F (85–93˚C). Use the cooking thermometer to check the temperature.

MATERIALS

→ 2 clear plastic cups per color

→ cold water

→ food coloring

→ 4 or 5 marbles

→ hot water

→ cooking or lab thermometer

1. Fill one plastic cup 3/4 full with cold water.

2. Wait until the water has become completely still.

3. Add a few drops of food coloring (fig. 1). What happens to the food coloring? Take a photograph or draw a picture of what you see.

Fig. 1: Add a few drops of food coloring.

4. Empty the cup.

5. Put the marbles in the bottom of the second cup.

6. Add hot water to the cup so that the hot water just covers the marbles (fig. 2).

Fig. 2: Add hot water to cover the marbles in the cup.

7. Put the first cup on top of the marbles and hot water (fig. 3). Fill this cup with cold water again.

Fig. 3: Put the first cup on top of the marbles and hot water.

8. Add a few drops of food coloring to the cold water (fig. 4). What happens to the food coloring this time? Take a few photographs or a video, or draw a picture of what you see happening over time (fig. 5).

Fig. 4: Add a few drops of food coloring to the cold water.

Fig. 5: Take photographs of what you see.

Heat Seesaw

Everything in nature seeks balance. Heat seeks balance, too. Heat flows from high temperature to low temperature. What happens if you pour hot water into a cold tub? The molecules of hot water are moving fast and will have more energy. These hot water molecules crash and collide into the colder molecules, giving them some of their energy. The hot water molecules slow down, having lost some energy, while the colder molecules start to speed up. The cold water becomes warmer, and the hot water gets cooler. This continues until all the water is the same temperature and all the water molecules are moving at the same speed. It’s like the hot and cold molecules are on a seesaw!

This seesaw happens in all substances: solids, liquids, and gases!

ENERGY EXPLAINED

You just observed heat—but what is it? Heat is the motion of molecules in a substance. The substance itself is not moving, but its molecules are constantly in motion. This motion is thermal energy, or heat. Heat always moves from areas of high temperature (high energy), to areas of low temperature (lower energy), until the temperatures equalize.

Liquids, like water, and gases, like air, are classified as fluids. Heat moves through fluids in a process called convection. In this lab, you created a convection current in your cup: When a fluid is heated, the warmer parts of the fluid become less dense and float to the top. Cooler fluids are denser than warmer fluids, so while the warm fluid floats to the top, the cool fluid sinks to the bottom. This cycle continues until the temperature of the fluid begins to equalize. In your cup, this may only take a few minutes, but in larger spaces or in nature, it can take a very long time.

BEACH BASICS

Sometimes on a hot day at the beach, you have to run from your blanket to the water. That sand is so hot! Why is the sand so much hotter than the water? And why, on a summer night, is the sand cooler than the water? This lab explores how heat, or thermal energy, can travel and be absorbed by substances. Do different substances absorb and hold their thermal energy differently?

TIME:
30 minutes or more

PERSON POWER:
No Sweat!

SAFETY IS KEY:
Be cautious when handling lightbulbs, as they may become hot when illuminated.

MATERIALS

→ 2 clear plastic cups

→ 2 cooking or lab thermometers

→ room-temperature sand

→ room-temperature water

→ timer

→ desk lamp with heat bulb or traditional incandescent bulb

1. Fill one cup with water (fig. 1).

2. Fill the second cup with sand so the sand and water are at the same level (fig. 2).

Figs. 1 and 2: Fill one cup with water and the second cup with sand.

3. Put a thermometer into each cup (fig. 3). Record the starting temperature of each cup. Make a table like the one shown here to record your data.

Fig. 3: Put a thermometer into each cup.

4. Place both cups about 4" (10 cm) away from the lamp (fig. 4). Turn on the lamp. Make sure that both cups are receiving approximately the same amount of light.

Fig. 4: Place both cups about 4" (10 cm) away from the lamp.

5. Set a timer for one minute and record the temperature in each cup every minute for ten minutes. Does one material have a higher temperature? Why?

6. Turn off the lamp and record the temperature every minute for ten minutes (fig. 5). Did one material cool more quickly?

Fig. 5: Record the temperature every minute for ten minutes

ENERGY EXPLAINED

Much of the Earth’s energy comes from the sun in rays or waves called radiant energy. When the sun’s radiant energy radiates toward the Earth, it hits molecules in the ocean, on land, in our bodies, and in the air. Those molecules turn some of this energy into heat. You’re creating a mini version of this process using your lamp. The heat (thermal energy) from the lamp radiated into the cups. The sand will heat up more quickly than water. However, when the lamp is turned off, the water probably stayed warmer longer than the sand. This is very much like what we experience during a day at the beach.

Some materials are able to absorb and release heat faster than others. Sand is one of these materials.

What a Breeze!

Wind is energy in motion, but where does it come from? As you learned in this lab, when the sun shines, land warms faster than water. Land absorbs energy from the sun quickly and changes it to heat. This means that the air just above the land will also be warmer than the air above the water. Warm air over the land rises and moves out toward the ocean, where it cools and sinks toward the water. When it does, the cooler ocean air moves in toward land. This is called a sea breeze—the refreshing, cool air from the sea. Overnight, however, this process reverses. Why? Think about what you observed in this lab. At night, the land cools more quickly than water. Since the ocean retains its temperature longer, the air above it stays warmer. Warm air rises up from the ocean and sinks down again when it reaches the land. The cooler land air rushes out to sea. This is called a land breeze. The movement of air in this fashion is what creates wind!

Now Try This!

Different materials absorb and retain heat in different ways. Does color or texture matter, too? Experiment by filling cups with different colors of sand and water and repeat the steps of the lab. Try it with cups of different materials like rocks or even a cup of air!

— DID YOU KNOW? —

At the beach, you’ll need less bug spray during the day than you will at night. Why? Because of the direction of the breeze! Fewer bugs hang out over the ocean, so when there’s a sea breeze there are fewer bugs to bite you!

BEACH BASICS DATA

TIME	LAMP		NO LAMP
	Sand	Water	Sand	Water
Starting
1 min
2 mins
3 mins
4 mins
5 mins
6 mins
7 mins
8 mins
9 mins
10 mins

WHAT A GAS!

We know that heat, or thermal energy, travels through solids and liquids well. But what happens when it travels through gases like air, oxygen, or helium? In this lab, we’ll trap some gas from our lungs (breath!) in a balloon and explore what happens when it’s heated or cooled.

PERSON POWER:
Grab a Crew Member! It might be handy to have help tying the balloon and holding it for measurements.

SAFETY IS KEY:
Use caution with the hot water. The hot water needed for this activity should be just under boiling, approximately 185–200˚F (85–93˚C). Use tongs or an oven mitt to place your balloon in the hot water.

MATERIALS

→ 1 or 2 round balloons

→ bowl of ice water

→ bowl of hot water

→ measuring tape

→ oven mitt or tongs

→ cooking or lab thermometer

1. Blow up the balloon to the size of a baseball and tie it (fig. 1).

Fig. 1: Blow up the balloon to the size of a baseball.

2. Allow the balloon to sit for a few minutes so that the gas in the balloon can equalize with the temperature of the room.

3. Use the measuring tape to measure the circumference of the balloon at its widest point (fig. 2). Circumference is the distance around a circular object.

Fig. 2: Measure the circumference of the balloon.

4. Check the temperature of the room using your thermometer. Keep in mind the size of your balloon at this temperature, or take a picture of it!

5. Fill a bowl with ice water. Place the balloon in the ice water for one minute (fig. 3). After one minute, measure the circumference of the balloon and the temperature of the water. Did you notice a change?

Fig. 3: Place the balloon in the ice water for one minute.

6. Fill a bowl with hot water. Using tongs or an oven mitt, carefully put the balloon in the hot water for one minute (fig. 4). After one minute, measure the circumference of the balloon and the temperature of the hot water. Did you notice a change?

Fig. 4: Carefully put the balloon in the hot water for one minute.

Don’t Step on a Crack!

Ever wonder why sidewalks become cracked? All materials expand when they’re heated and contract when they’re cooled. When sidewalks and roads heat up and cool down as the seasons change, they expand and contract, too, which can cause cracks. When sidewalks and roads are designed with seams or joints between sections, the surfaces can expand and contract without cracking.

Now Try This!

Perform the experiment again, but this time, use a kitchen scale to take the mass of the balloon at the start and again after you take the balloon out of the hot and cold water. When the balloon changes size, does it change its mass? Mass is a measure of the amount of matter—has the amount of matter in the balloon changed?

Use a kitchen scale to take the mass of the balloon.

ENERGY EXPLAINED

When thermal energy (heat) is applied to a substance, its molecules move faster and push apart from each other. The spaces between the molecules become greater. When you put your balloon in hot water, it got bigger. The molecules of your breath stayed the same size inside the balloon but moved more rapidly and pushed apart, causing the balloon to expand. The opposite occurred when you put the balloon in the ice water. As heat energy is taken away, molecules slow down and move closer together, causing the balloon to shrink!

All substances expand when they’re heated—solids, liquids, and gases! Some expand a little and some expand a lot.

SHADOW SHAPER

We use light energy every day. Light that we see is called visible light, and it travels like waves in straight lines. But light can’t pass through most objects. This lab will explore how shadows are created when something blocks light’s path.

TIME:
15–20 minutes

PERSON POWER:
No Sweat!

MATERIALS

→ 11" × 17" (28 × 43 cm) piece of white paper

→ tape

→ table or flat surface near a wall

→ flashlight, (single bulb, non-LED works best)

→ small object, such as a wooden spool or nail polish bottle

→ ruler

→ notebook and pencil

1. Tape the paper vertically on the wall closest to the table (fig. 1). The bottom edge of the paper should be at the same level as the table top.

Fig. 1: Tape the paper vertically on the wall.

2. Place the flashlight on the table 12" (30 cm) from the paper (fig. 2). Orient the bulb so that the light points at the paper.

Fig. 2: Place the flashlight 12" (30 cm) from the paper.

3. Measure the height of the small object (fig. 3). Record the height so you remember it later. Draw a table like the one shown here, if necessary.

Fig. 3: How does the shadow change with each movement of the object?

4. Position the small object between the flashlight and the paper, so that the middle of the object is 2" (5 cm) from the paper on the wall.

5. Measure the height of the shadow. Notice how clear or blurry the shadow and its edges appear. How does the height of the shadow compare to the height of the object? Record your observations on the chart.

6. Move the object back so that it is 4" (10 cm) from the paper on the wall. How has the shadow changed?

7. Continue moving the object closer to the flashlight, at distances of 6", 8", and 10" (15, 20, and 25 cm) from the wall. How does the shadow change with each movement of the object (fig. 4)?

Fig. 4: How does the shadow change with each movement of the object?

Sundial

Early Egyptians knew all about shadows and how light travels. They observed that the sun follows the same pattern in the sky each day. They realized that as the position of the sun changes in the sky, so does your shadow. They used their observations to create a tool for telling time. This device, a sundial, was made simply by placing a stick in the ground. They used the length and position of the shadow to tell them the time of day!

Now Try This!

Hold the flashlight at a different angle. How does your object’s shadow change? Have some time on your hands? Go outside on a sunny day and have a friend take a picture of your shadow. Mark the spot where you stood, and come back to repeat this process every hour for a few hours. How does your shadow change and why? Come back to the spot a few months later at approximately the same times. Does your shadow change?

ENERGY EXPLAINED

Light energy travels in waves called radiant energy. We call the light we see “visible” light, because we can’t see the actual light waves. What we see is the reflection of light off substances. Not all radiant energy can be detected by the eye. Radio waves, X-rays, and cell phone signals also travel as radiant energy that can be detected by special devices.

Our eyes are a special instrument for detecting light. We see objects only because light waves are reflected off an object and into our eyes.

Light waves travel in straight lines and do not change direction unless they are reflected or refracted (bent). When light hits the wooden spool, for example, it cannot pass through or go around it. The spool blocks the light from reaching the wall and an area without light is created. We call the areas without light “shadows.”

As you move an item closer to a light source, its shadow appears larger because the object is blocking more light. As you move the item further away from the light source, the shadow becomes smaller and sharper because the object is blocking less light.

SHADOW SHAPER DATA

FLASHLIGHT DISTANCE TO WALL	OBJECT DISTANCE TO WALL	SHADOW HEIGHT	SHADOW CLARITY
12 inches (30 cm)	2 inches (5 cm)
12 inches (30 cm)	4 inches (10 cm)
12 inches (30 cm)	6 inches (15 cm)
12 inches (30 cm)	8 inches (20 cm)
12 inches (30 cm)	10 inches (25 cm)

MIRROR MADNESS

When light strikes an object, it can pass through the object, be absorbed by the object, or be reflected by the object. This lab will explore how light can bounce off an object in a straight line. You’ll be making your own fun house of mirrors!

TIME:
30 minutes

PERSON POWER:
If you have nine stuffed toys, you can do this activity by yourself or with the help of a friend. Otherwise, grab nine crew members, because it’s All Hands on Deck!

SAFETY IS KEY:
This activity requires a full-length mirror. Ask for help from an adult to move and orient your mirror for the lab. Mirrors can be heavy and are breakable. Be careful when you move mirrors, especially if you’re superstitious!

MATERIALS

→ full-length mirror

→ measuring tape

→ 9 stuffed toys (or friends)

→ sticky labels

→ colored pencils

→ paper

→ protractor

1. Place the mirror vertically against a wall. Hang or place it on top of a few stacked books, so that it is 8" (20 cm) off the floor (fig. 1).

Fig. 1: Place the mirror so that it is 8" (20 cm) off the floor.

2. Make labels for your nine stuffed toys (or friends), each one with a number 1 to 9 (fig. 2).

Fig. 2: Make labels for your stuffed toys (or friends).

3. Position toy 5 so it is 60" (1.5 m) from the center of the mirror (fig. 3).

Fig. 3: Position toy 5 so it is 60" (1.5 m) from the mirror.

4. Position toys 1 through 4 to the left of toy 5 (fig. 4), each one 16" (41 cm) away from the next. Do the same with toys 6 through 9 on the right. All the toys should be in a straight line, 60" (1.5 m) from the mirror wall (fig. 5).

Fig. 4: Position toys 1 through 4 to the left of toy number 5.

Fig. 5: All the toys should be in a straight line.

5. Draw a diagram of the mirror and the toys.

6. Stand directly behind toy 1, kneel to its level, and look directly into the mirror (fig. 6). Which toys can you see? On your diagram, draw a straight line with a colored pencil from toy 1 to the mirror and from the mirror to any toy you see.

Fig. 6: Stand behind toy 1 and kneel to its level.

7. Stand directly behind toy 2. Using a different color, repeat step 6 and draw your lines. Repeat this for all nine toys.

8. Use a protractor to measure the angles you drew.

To Reflect or to Absorb?

Light waves can be reflected by mirrors, but reflection happens even if an item isn’t shiny. Different materials reflect light differently based on their color, texture, and other properties. Light waves (radiant energy) can also enter a substance and change into other forms of energy. Our skin absorbs light energy and turns it into heat (thermal energy). Some things are better reflectors than others in nature. Snow and ice reflect light better than forests. Glass buildings and homes with light-colored paint reflect more light than a home made of stone or painted with dark colors.

ENERGY EXPLAINED

We see light waves that bounce off things—the light that is reflected. When you look at the person next to you or at your image in a mirror, you’re seeing reflected light waves! In this lab, you’re seeing light reflected off the stuffed toys. Some light waves travel toward the mirror and the mirror reflects them. Some of the waves from the mirror make it to your eyes.

Light waves are reflected at predictable angles. It’s very much like when you bounce a ball. If you drop the ball straight down, it is going to bounce straight back up, not left or right. Light waves move the same way. When light waves hit an object, they reflect back at the same angle, in a straight line.

RAMP IT UP!

When you look around you, many things may be in motion. All of this motion takes energy; nothing can move without it. In this lab, you’ll use ramps and marbles to explore the basics of motion and energy: What gets things moving, keeps things moving, and what makes things stop moving.

TIME:
20 minutes

PERSON POWER:
Grab a Crew Member! It’s easier to have help finding your marble if it goes missing!

MATERIALS

→ 5 books (all the same thickness)

→ ruler with a grooved center channel

→ pencil and paper or notebook

→ marble

→ measuring tape or meter/yardstick

1. Place one book on the floor (a smooth floor works best). Put the end of the ruler on the edge of the book binding and allow the ruler to extend out like a ramp.

2. On a piece of scrap paper or in a notebook, create a data table like the one on the right.

3. Place the marble at the top of the ruler and let it go. Let it roll down the ramp (fig. 1). Don’t push it!

Fig. 1: Place the marble at the top of the ruler and let it go.

4. Allow the marble to come to a stop. Stretch the measuring tape from the bottom of the ruler ramp to the marble to see how far the marble traveled (fig. 2).

Fig. 2: Stretch the measuring tape from the ruler ramp to the marble.

5. Record the distance and repeat two more times for a total of three trials. Calculate the average distance traveled for the marble at a ramp height of one book.

6. Repeat the trials, adding a book each time, until your ramp is five books high (figs. 3 and 4). How did the height of the ramp affect the marble’s motion?

Fig. 3: Repeat the trials, adding a book each time.

Fig. 4: Repeat the trials until your ramp is five books high.

RAMP IT UP DATA

RAMP HEIGHT	TRIAL 1	TRIAL 2	TRIAL 3	TRIAL 4
1 Book
2 Books
3 Books
4 Books
5 Books

Now Try This!

Try the experiment on different surfaces, such as carpet, a wooden deck, grass, or asphalt.

ENERGY EXPLAINED

All moving objects have energy. If an object isn’t moving, it’s storing energy until it is made to move. Your marble on the top of the ramp has energy. It’s not moving, but it has the potential to move. We call this potential energy. But if you didn’t give your marble a push, how does it get rolling?

Three hundred years ago, a famous guy you may have heard of, Sir Isaac Newton, figured out some major patterns related to motion. We call these Newton’s Laws of Motion. Newton’s first law states that in order for an object to move, a force must act upon it to make it move. It also states that a moving object will keep moving until a force acts on it to make it stop.

In the case of your marble, what makes it begin to move is a force called gravity. Gravity pulls things toward the ground and is what gives an object its potential energy. Height can affect the force of gravity on an object: the higher the object is from the ground, the more force it will have coming down. Your marble probably rolled farther, and maybe even faster, when the ramp was higher.

But what made your marble stop? It probably slowed to a stop. Why? As the marble rolls on the floor, it’s making contact with air and the floor’s surface. Both of those items push back against it, slowing it as it rolls and creating heat, just as if you rubbed your hands against one another. This force is called friction. Different surfaces contribute differently to friction. Did you ever go skating on the kitchen floor with your socks on? It just doesn’t work the same way on carpet, because carpet is a high-friction surface. Using a smooth, flat table will keep your marble rolling longer than a surface like carpet or grass.

PENDULUM SWINGER

Motion doesn’t always happen in a perfectly straight line. For example, if you get on the swings at a playground, why does the swing follow a curved path? Swings are examples of pendulums, and this lab sets up a mini pendulum to explore how gravity and motion work together.

TIME:
30 minutes

PERSON POWER:
All Hands on Deck! This activity works best with a few friends: one to work the stopwatch, one to do the swinging, and one to do the counting.

MATERIALS

→ meter/yardstick

→ 2 tables or desks of the same height

→ piece of string, 2' long (61 cm)

→ several large 1/2" (1.3 cm) washers

→ stopwatch

→ measuring tape

→ masking tape

1. Place the yardstick across the two tables or desks.

2. Tie one washer to the end of the string.

3. Tie a loop at the other end of the string. Slide the loop onto the yardstick so that the washer hangs between the tables (fig. 1). Tape the loop in place on the yardstick, and tape the yardstick to the tables (fig. 2).

Fig. 1: Tie a loop in the string and tie it onto the yardstick.

Fig. 2: Tape the loop into place.

4. Raise the washer to the side so that the string is taut and the washer is at the same height as the yardstick (fig. 3).

Fig. 3: Raise the washer to the side so that the string is taut.

5. Set your stopwatch for ten seconds.

6. Let the washer go, allowing it to swing back and forth (fig. 4). Count each complete back and forth motion the washer makes in ten seconds. Each back and forth is called one vibration. Make a table or chart to keep track, if needed.

Fig. 4: Let the washer go, allowing it to swing.

7. Remove the tape and slide the string off the yardstick. From the top, slide another washer down the string so it rests on the first washer. Reattach the string to the yardstick and tape it back into place so the washers hang between the tables.

8. Repeat steps 4 to 6. Do you see a difference? Add another washer or two and repeat. What do you observe?

9. Now try changing the height where you release your washer. Do you notice a difference?

Now Try This!

Try the experiment again with one washer. This time, however, shorten the string by half the length. Do you think the vibrations will increase or decrease? Continue adding washers each time and compare.

ENERGY EXPLAINED

All objects experience the force of gravity. When possible objects in motion move in a straight path. In the case of the pendulum, the object doesn’t move in a straight line, it moves in a curved path. Why?

The pendulum is anchored at the top. The yardstick holds the string at a center point, and a force called centripetal force pulls the pendulum upward when you let go. Gravity and centripetal force work together, pulling in opposite directions, to make the pendulum swing back and forth in a curved path.

You probably didn’t see much change in the vibrations when you added extra washers, increasing the mass. Mass does not affect a pendulum’s swing. However, you will see a big difference in the vibration when you change the height of the pendulum’s release. The higher you hold the washer, the longer it takes it to go back and forth.

SLINKY WAVES

Sound is energy. It travels in waves, but these waves are different than the waves that carry light, X-rays, radio signals, or even water. This lab explores the different types of wave motion to understand how sound energy is carried from one place to another.

PERSON POWER:
Grab a Crew Member! You’ll need a partner or two to complete this activity.

MATERIALS

→ Slinky spring

→ long table

1. Your partner should stand across from you, holding one end of the spring, while you hold the other end (fig. 1). Another friend can record a video of the activity. It’s really fun to view this in slow motion!

Fig. 1: Your partner should hold one end of the spring.

2. Your partner’s end of the spring should be completely still while you move your end up and down slowly, about 4" (10 cm) off the surface. The motion should mimic ocean waves (fig. 2).

Fig. 2: The motion should mimic the waves of the ocean.

3. Move the spring more quickly, but at the same height. Does it respond in the same way?

4. Slow the movement down again, but increase the height to 8" (20 cm) off the surface (fig. 3). Observe the spring motion compared to the lower height, and then move it more quickly as in step 3. Has anything changed?

Fig. 3: Slow the movement down, but increase the height of the spring.

5. Now your partner should move the spring while you keep your end still (fig. 4).

Fig. 4: Keep your end of the spring still while your partner moves the other end.

6. Have your partner slowly push and pull the spring 6" (15 cm) forward and backward on the surface in a straight line, toward you. How does the spring respond this time?

7. Increase the speed of the forward and backward motion and observe. What happens when you increase the length of movement to 12" (30 cm)?

Now Try This!

Explore the amplification of sound by inserting the bottom of a foam cup into a metal slinky. Hold the slinky up by your head and bounce it straight down to the ground and back. Then try holding it closer to the ground and bouncing it. What do you observe?

ENERGY EXPLAINED

Energy can travel in waves. Not all energy waves travel in the same manner. Ocean waves, visible light, and X-rays travel in an up and down motion. This is what you observed in the first half of the activity. When you moved the spring up and down on your end, the wave traveled forward.

Sound waves move differently. Sounds are caused by energy vibrating through things or by molecules moving back and forth. The molecules collide and pass on their energy in the same direction as the sound. You demonstrated this with the spring in the second half of the lab. As the spring is pushed forward, each piece pushes into the next piece, moving the energy forward, too. This is often called a longitudinal wave because it moves in one long line.

You can often feel the vibrations of sounds moving through you! Have you ever been to a loud concert or sporting event where you could feel the vibration as music thumped loudly? Place your fingers on your throat and hum a tune. Can you feel the vibration? Sound can vibrate and push its energy through liquids, gases, and solids, too. Energy, such as light, that travels in an up and down pattern is often stopped by a solid barrier.

SOUND STOPPER

Sound waves travel in long lines and vibrate through materials. So, what makes a room soundproof? Often we can hear sounds through thick and heavy-duty materials. Will a material stop sound? This lab explores how sounds vibrate through various solids.

TIME:
30 minutes

PERSON POWER:
Grab a Crew Member! You’ll need a partner or two for this activity. You’ll take turns listening.

MATERIALS

→ smartphone with your favorite song downloaded

→ piece of paper

→ sweatshirt

→ cookie sheet

→ roll of paper towels

1. Sit facing your partner, about 3' (91 cm) from each other. Place your materials between the two of you.

2. Hold the phone so that its speaker is aimed toward your partner. Press “play” on your song, and then place the paper so that it’s between the speaker and your partner (fig. 1). It should be close to the speaker, but not touching it. Ask your partners to tell you what they observe about the song before and after you move the paper into place. Do you notice anything different about the song on your side of the paper?

Fig. 1: The motion should mimic the waves of the ocean.

3. Keep the volume the same on your phone, start the song again, and repeat the process with the sweatshirt, cookie sheet, and roll of paper towels. Discuss what you hear each time with each item.

4. Switch roles and repeat (figs. 2–4).

Figs. 2–4: Repeat the process with the sweatshirt, the cookie sheet, and the roll of paper towels.

5. Try substituting any type of barrier you wish! What items are great at stopping the sound? What items amplify the sound?

Blind as a Bat

If you’ve ever heard this phrase, you’ll know that bats have poor eyesight. Bats actually use sound waves to help them “see” while flying. Bats can tell where objects are by listening to how sounds are reflected. They emit a sound that travels out and then back to them. If sounds are reflected quickly, they know to change direction. Bats can even find the insects they feast on using sound waves!

ENERGY EXPLAINED

Sound waves move through the air in a straight line. When sound reaches an object, just like light, it can either be reflected or absorbed. You have probably heard reflected sound waves before: an echo. Harder objects are more likely to reflect sound waves. When you played the song with the cookie sheet in front of the speaker, the music was more likely to bounce back toward you. Your partner probably heard a more distorted, faint version of the song because the sound waves had trouble vibrating through the cookie sheet.

Some objects absorb sound waves. When you held the paper in front of the phone, the song was absorbed by the paper and then traveled through. Your partner was probably able to hear most of the song. The sweatshirt, however, was likely a better absorber. Your partner likely heard the song at a lower volume, maybe even muffled, depending on the thickness of the sweatshirt. In your home, carpets and curtains help to absorb sounds and slow the vibration of sound energy.