Outline: What is a wave? What is a wave? Properties of waves? Properties of waves? Check your understanding! Check your understanding!

What is a wave? First thing comes to mind, ripples spreading out on water surface when you throw a rock in the lake. Ocean waves, sure those are waves! The TV broadcast signals are transmitted in forms of electromagnetic waves Sounds are waves too, this is a picture of visualized sound waves for some noise. Lights are waves, the natural sunlight contains 7 different colored lights. Each light wave appears its own color is because they have slight different properties. All of them are waves! Waves are everywhere, these are just some examples.

What is a wave? A wave is a disturbance that travels from one location to another location. Pay attention to What the person did to start the wave? This is what we meant by disturbance. Sounds are in forms of waves too. Can you explain how we make disturbances when we talk (generate sound waves)? Similarly, throwing a rock in the lake is making a disturbance. Water ripples spreading out is the wave traveling to further locations.

What is a wave? The traveling disturbance in a wave is carrying energy. The traveling disturbance in a wave is carrying energy. Think about ocean waves. When the wave hits shore, it has so much energy that can sometimes destroy trees and houses. What happens to the boat when a wave hits it? What happens after the wave travels past it? What happens to the boat that’s further away? Carries energy to make the boats move How exactly does a wave carry energy? Let’s make some waves with a rope and find out!

What is a wave? Waves travel through medium. Waves travel through medium. The string is the medium for the wave we just made. Water molecules is the medium for ripples and ocean waves. Air molecules is the medium for sound. What happens if there isn’t a medium for the wave to travel through? Say we make a disturbance and there is no string. Or when we talk in outer space. Medium segments interact with each other to cause the next segment start moving, that’s how energy is carried on.

What is a wave? Can you tell which ones are waves and which ones aren’t? Can you tell which ones are waves and which ones aren’t? Point out the medium if it is a wave. Point out the medium if it is a wave. If the man shakes his hand up and down, will he make a wave? Jumping Rope? Is it carrying a wave?

What is a wave? A mini waterfall, is it a wave? What’s the difference between this and ripples?

What is a wave? When a gun is fired, does it create waves?

What is a wave? Are wind waves? What happens if the dog blows on it?

What exactly is a wave? From the examples, we can see that a wave passes on energy, not matter. From the examples, we can see that a wave passes on energy, not matter. Energy is passed along the wave, and make the medium vibrate. Energy is passed along the wave, and make the medium vibrate. Because medium interact with each other, a vibrating medium segment causes the adjacent segment to vibrate, then the adjacent segment causes its adjacent segment to vibrate, thus energy is passed further. Because medium interact with each other, a vibrating medium segment causes the adjacent segment to vibrate, then the adjacent segment causes its adjacent segment to vibrate, thus energy is passed further.

Properties of waves Waves can look very different depending on the source. Waves can look very different depending on the source. There are many more kinds of waves. Here are just some examples.

Properties of waves Most waves in nature look like this. Most waves in nature look like this. Recall the waves on the string we made. Do they look like this one? How does water ripples fit into the wave graph? There are a lot of waves spreading out in all the directions. If we take a cross-section, we will see how each wave look like. One Cross-section

Properties of waves Amplitude Crest Trough How would the wave move? Recall the wave on the string we made. The entire wave will move to the right on the string, because you are making disturbance on the left end. Wavelength

Properties of waves If we keep making the same disturbances, a lot more of these wave segments will appear. And they will all look the same. Keep track of the red wave segment, this is the first wave generated.

Properties of waves If two waves have different properties, they are likely to appear different. If two waves have different properties, they are likely to appear different. Remember we said lights are waves too? Lights appear to be a certain color is because they have different wavelength.

Properties of waves The brightness of a light depends on the amplitude. Least bright Ok bright Brightest Note, waves themselves do not have colors. It’s the energy their carrying that excites our vision system so that our brain see them in certain colorful ways. Dog’s brain can not do that, so they can not see color.

Properties of waves For sound waves, the AMPLITUDE determines how LOUD the sound is. Wavelength determines the PITCH of the sound. Let’s make some noises and see for ourselves! Look at the first row. One is louder than the other one. What makes them different? Look at the first column. One is high pitch (note), the other is low pitch. What makes them different?

Some Questions Now So far you have learned quite a bit about waves. Now I will ask you some challenging questions to see if you REALLY understood the concepts we are dealing with here. Most of them will require some independent thinking or even guessing, so don’t worry if you get them wrong. The purpose is to get you to think! So far you have learned quite a bit about waves. Now I will ask you some challenging questions to see if you REALLY understood the concepts we are dealing with here. Most of them will require some independent thinking or even guessing, so don’t worry if you get them wrong. The purpose is to get you to think!

Medium or No Medium? How can we see the sun from earth? How can we see the sun from earth? Is there any medium to transmit the light waves to earth? Is there any medium to transmit the light waves to earth? Wait a minute! How is it possible that these waves can travel without medium???

Question: How can light waves travel WITHOUT medium? Hint: Recall what medium did in the rope wave. Is there a way we can have some sort of way to pass on energy without matter? Nature has a clever way of doing it, guess what it is? The answer is ELECTROMAGNETIC WAVES ! When a light source gives out light, it generates electromagnetic waves to travel in all directions. Instead of a medium, these waves store energy in electric and magnetic fields, and pass on energy by shifting these fields. Electric field Magnetic field

Assorted Facts… As you can see, the ELECTROMAGNETIC WAVES are very different from the other waves in the ways of traveling. As you can see, the ELECTROMAGNETIC WAVES are very different from the other waves in the ways of traveling. We call the other waves MECHANICAL WAVES because they need matter (medium) to “mechanically” pass on the energy. We call the other waves MECHANICAL WAVES because they need matter (medium) to “mechanically” pass on the energy. Ex: Ocean waves, ripples, sound waves, waves on a rope…

Electromagnetic Waves? What waves are electromagnetic waves? (Hint: waves that do not need medium to travel) What waves are electromagnetic waves? (Hint: waves that do not need medium to travel)

Speed of a wave? How do you calculate the speed of a wave? How do you calculate the speed of a wave? “Hello!” 680 m Tom and Marry are 680 meters apart. Tom says “Hello” to marry. It takes her 2 seconds to hear it. What’s the speed of the sound wave?

Speed of a wave? Will it take more or less time for Marry to hear Tom if they were talking in water? Will it take more or less time for Marry to hear Tom if they were talking in water? 680 m Hint: Think about the media the waves travel in. Which one would carry on energy faster?

Speed of a wave? For mechanical waves (such as sound waves), medium affects the speed of the wave. What about electromagnetic waves? For mechanical waves (such as sound waves), medium affects the speed of the wave. What about electromagnetic waves? The speed of electromagnetic waves are not affected by the medium they travel in. They don’t use it anyways! Unlike sound waves and waver waves have different speeds of their own, ALL ELECTROMAGNETIC WAVES HAVE THE SAME SPEED! ,000,000 meters/second

Here are all the electromagnetic waves you can think of. They ALL have the speed of 3x10 8 m/s. Here are all the electromagnetic waves you can think of. They ALL have the speed of 3x10 8 m/s.

Period? If a wave is moving to the right, how far does it have to move to make it identical to the what it looks like now? If a wave is moving to the right, how far does it have to move to make it identical to the what it looks like now? Wavelength The time it takes a wave to move a wavelength long, is called PERIOD. We use T to refer to it.

Period, speed and wavelength? If a wave moves at a speed of v meters/second, If a wave moves at a speed of v meters/second, and has a wavelength of λ meters, what is the period T? λ meters How much time to move this far? Hint: time=distance/speed

Frequency and period? If I tell you a waves frequency is the reciprocal of its period. What does frequency represent physically? If I tell you a waves frequency is the reciprocal of its period. What does frequency represent physically? frequency = 1/T Hint: If a wave moves one wavelength long every 3 seconds, then for each second it moves 1/3 wavelength.