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Course: Middle school physics - NGSS > Unit 4
Lesson 2: Mechanical waves and lightMechanical waves and light
Mechanical waves and light waves are two different wave types that can both be represented with a model. Mechanical waves require a medium like air, water, or a rope to travel through. On the other hand, light waves, which are a type of electromagnetic wave, don't need a medium. They can travel through the vacuum of space. Wave properties can also be represented as the brightness and color of light. Created by Sal Khan.
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- what is the light with the highest wavelength called(13 votes)
- red has the longest wavelength, at around 700 nanometers.(16 votes)
- I really don't get this?(2 votes)
- What do you not understand? I'm here to help and to answer questions. Also to upvote, downvote and flag anything unhelpful.(13 votes)
- What types of energy in thermal energy.(1 vote)
- Thermal Energy is the energy that heat (or the lack of) produces. If you use a thermal imaging camera, you'll see that a stove top burner perhaps, is far brighter then the inside of a refrigerator, as the burner is HOT and the fridge is COLD.(12 votes)
- Do waves have mass?(5 votes)
- Waves carry energy and according to E = mc squared. Energy = mass. If waves are carrying energy then they are also carrying mass.(1 vote)
- 1:15this means that my ears are telling me that someone is telling me how my ears tell me things.(4 votes)
- Let's not confuse anyone...(2 votes)
- Wait, so... Radio is light? and it turns into sound?(4 votes)
- Visible light is a small part of the electromagnetic spectrum. Radio waves are light except that we can't see it or hear it. Our radio converts the radio wave into sound.(2 votes)
- What is the trough(4 votes)
- The lowest point of the wave.(2 votes)
- at3:10he says mechanical waves are the ones you "see" most often, however "seeing" is actually your eyes sensing the differences in light waves, so wouldn't light waves be tyhe ones you see more often?(3 votes)
- He's talking about "seeing the subject" of the kind of wavelength.(3 votes)
- Why is boll lightning so rare?(4 votes)
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Video transcript
- [Instructor] Let's talk about waves. So let's imagine that
you were to take a string and attach it at one end to a wall, and then on the other end, you were to wiggle it up and down. Well, then you would have made a wave. You would see a pattern
that looks like this. Now, what would be a good
definition for a wave? Well, we could call it
a traveling disturbance. Well, what does that mean? Well, we're disturbing the rope. If we didn't move it, if
we just held it straight, it might look something like that, or it might just hang down a little bit, but clearly we are now
moving it up and down, and those movements are
disturbing that rope and that disturbance can
move along that rope. Now, we see waves not just in ropes that are moving up and down. You have probably seen water waves. If you were to take a
tank of water like this and if you were to start
pressing on one end of the water here, you would see these wave forms that start. We can also see that with
sound and sound waves. You might not realize it, but the sound of my voice right now is actually just a traveling compression, or disturbance in the air
that is getting to your ear. And that little hairs in your ears can sense those changes
in pressure from the air and your mind perceives that as sound. And once again, this is
a traveling disturbance. You have particles that
have high pressure, and then they knock into
the particles next to them, that then knock into the
particles next to them. So if you were to be able to
observe this in slow motion, you would see these high
pressure parts right over here could be traveling, say to the right. And even though this
might be a pressure wave that's traveling through the air, we can represent it in a way that looks a lot like our first rope that we were moving up and down. Areas where things are
high, in the sound example, that's high pressure, and you have areas where things are low, in the sound example,
that is low pressure. Now, when we talk about waves,
there are common properties. For example, we might wanna know, how much are we getting disturbed from what we would call the equilibrium? You could view that as maybe the middle state right over there. Well, if we're getting
disturbed that much, we could call that the amplitude. That's how much we are going above or below that equilibrium. This would be the amplitude as well. We could think about how far is it from the same points on the wave. So if we go from one peak to another peak, well, we could call that the wavelength, and you could just do it from
any one point on the wave that's just like it on the wave again. So that would be the same wavelength as our original wavelength
right over there. You might hear the term
frequency of a wave. And one way to think about that is if you were to just
observe our original rope, and if you were to say, "How many times does it go all the way up, all the way down, and then back up. so it completes a full cycle? How many times can it do that in a second? If it does that five times in second, then someone might say it has a frequency of five cycles per second. Now, everything that we
have just talked about, these are called mechanical waves. It's a special category, probably the ones that
you will see most often. Now, mechanical waves need
a medium to travel through. In the rope example,
the medium was the rope. In the water example, it's the water. In the sound example,
the medium is the air. Now, there are things that
can be described as waves that don't need a medium. In particular, and this is kind of mind boggling, is that light can be considered a wave. If we think about the
different frequencies of light, our brain perceives that
as different colors. And if we think about
the amplitude of light, our brain perceives that
as the intensity of light, how bright it is. And even more mindblowing, visible light are just certain frequencies of what we would call
electromagnetic waves. There's actually higher frequencies
of electromagnetic waves that have all sorts of applications. You might have heard of ultraviolet light, or x-rays, or gamma rays. Similarly, there's lower
wavelengths of light. You might have heard things
like infrared, or radio waves. These are all just different frequencies of what's known as electromagnetic waves.