Wave Properties

Every sound you hear travelled through the air in a wave before entering your ear. And every time you turn on a lamp, you send light waves shooting off. All waves move energy, in fact, a wave is the movement of energy.

Some waves can only travel through matter. For example, sound waves need matter in order to travel. They can travel through solid, liquid or gas. Other waves, like light waves, don't need matter to travel. They can journey through empty space. That's how light from the sun reaches us. It travels through empty space.

Which of the following is true about all waves?

• They enter your body through your ear.

• They need matter to travel through.

• They represent the movement of energy.

• They cannot travel through empty space.

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NGSS.MS-PS4-1

Sound waves usually travel through the air, though they can also move through liquid, like water, or through a solid, like a wall. Sound waves are created by a vibrating object.

The vibration of the object sends out sound waves. When a sound wave is very powerful, you can even feel the vibrations. That's why when you're at a concert, you can sometimes feel vibrations from the music. You hear sound because your ear detects the vibrations moving through the air. Inside your ear is an eardrum. It is a thin membrane that picks up vibrations.

Which of the following is true about the eardrum?

• It turns all kinds of waves into vibrations.

• It picks up vibrations from sound waves

• It’s a liquid that sound waves travel through.

• It’s a solid wall in the ear that blocks vibrations.

Light is an electromagnetic wave. That means it's a wave of energy that can travel through empty space. Light is special because it is the only kind of electromagnetic wave that humans can see. When you see an object, you are actually seeing light hit it and then bounce into your eyes. There are other types of electromagnetic waves, like the microwaves that heat your food, but humans can't see them.

Electromagnetic waves

• can all be seen by humans.

• don’t need matter to travel.

• are always invisible to humans.

• only travel through solid food.

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NGSS.MS-PS4-2

Think of the shape of a wave. It looks like a squiggly line. We know the highest part of that line is the peak. The wavelength is the distance between wave peaks. Waves of the same type can differ in wavelength. For example, the wavelength of light waves determines its color.

Amplitude is the measurement of a wave's height. It is measured in two ways. Peak-to-peak amplitude is the distance between the peak (the topmost part of a wave) and the trough (the lowermost part). Semi-amplitude is half the peak-to-peak amplitude. Most of the time when people refer to "amplitude," they are referring to the semi-amplitude: the distance from the middle of the wave to the top, or the middle of the wave to the bottom. The amplitude of a sound wave determines its volume.

Which of the following best explains the relationship between peak-to-peak amplitude and semi-amplitude?

• Semi-amplitude is half the distance of the peak-to-peak amplitude.

• Semi-amplitude is the same distance as the peak-to-peak amplitude.

• Semi-amplitude is double the distance of the peak-to-peak amplitude.

• Semi-amplitude is always greater than the peak-to-peak amplitude.

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NGSS.MS-PS4-1

A wave does not make whatever it is moving through travel with it. Waves in the ocean do not move water from one location to another. If they did, all the water in the ocean would empty onto the shore. Instead, waves are the movement (or transfer) of energy. During this transfer of energy, waves do make matter vibrate, or move in place.

Waves don't make matter move. However, there is an exception at the seashore, where the ocean meets the land. As seawater nears the land, the water is displaced because of a lack of space where the ocean floor slopes up. At the shoreline, waves literally topple forward onto the beach.

Which of these best shows how waves can affect matter?

• the moon’s gravity pulling the ocean a few feet up and down each day

• light appearing as color to the human eye

• a ship moving very quickly across the Atlantic Ocean

• a buoy bobbing up and down in place with ocean waves

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NGSS.MS-PS4-2

Different types of waves travel at different speeds. For example, sound waves travel more slowly than light waves. Have you ever been in a big empty room, or in a cave, and heard an echo? Echos happen because sound waves take time to travel to the wall and bounce back to your ears. But light is different. Light is much faster than sound. Light is the fastest moving thing in the universe.

Because light waves and sound waves travel at different speeds, you can figure out how far you are from a storm by watching for lightning and listening for thunder. Lightning and thunder are actually the same thing! Thunder is just the sound that lightning makes. Because light is so quick, you see the lightning flash first. The sound travels more slowly, so you hear the thunder after.

How do lightning and thunder illustrate the relationship between light and sound waves?

• Light moves faster than sound, so you hear thunder after you see lightning.

• Sound moves faster than light, so you see lightning after you hear thunder.

• Lightning and thunder are the same, so light and sound waves move together at the same time.

• Sound moves light, so when you hear thunder you know lightning will move toward you.

The topmost layer of the Earth is made up of large pieces that fit together like a puzzle. However, these pieces don't stay still, and sometimes they rub against each other. When these large sections of the Earth’s crust, called tectonic plates, hit each other, they send vibrations through the surface of the Earth. These vibrations are seismic waves. Seismic waves are just like the ripples in a pond. But instead of traveling through water, they travel through the Earth. When they reach the Earth's surface, they make the ground shake. That's an earthquake.

Earthquakes are the result of

• ripples traveling through water.

• Earth’s topmost layer sinking.

• vibrations from seismic waves.

• tectonic plates staying still.

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NGSS.MS-ESS3-2

Which of these does NOT create waves?

• water in the ocean

• light from the sun

• sound from a radio

• rain from the sky

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NGSS.MS-PS4-1

What is one thing that describes the motion of all waves?

• it's always fast

• it's always slow

• it always repeats

• it starts and stops

What is the top of a wave called?

• the peak

• the amplitude

• the wavelength

• the pattern

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NGSS.MS-PS4-1