![]() As we shall see it has proven to be a very powerful tool for measuring velocities in astronomy. In this short tutorial we will discuss the “Doppler Effect” and some of the many uses it has in astronomy. The answer to all these questions is the Doppler Effect. How is it we know how fast stars and galaxies are moving towards or away from us? How can we discover a star is double even if the separation of the two stars is too close to be resolved in even the largest of our telescopes? How did we discern the true rotation periods of the planets Mercury and Venus? How can we know how fast a star is rotating? How was the first planet orbiting a star outside the Solar System discovered? One of the greatest astronomical discoveries of the twentieth century was the expansion of the universe, how was that uncovered? Some are approaching us some are moving away but how do we know this? It would shift by a certain amount that depends on the speed of the car. It would bounce back at you, that frequency would shift. There's a car chase, and there's a car heading toward you. But in this case it wouldīe the speed of the blood. You know-this is dependent on the speed of the thing that was moving. Off of moving objects, and come back at you. This is some sensitive piece of equipment that wants to image, that wants to scan the blood flow and know howįast is the blood flowing. Imagine, instead of a gym this is a vein inside of your body. No, the bodybuilder didn'tĮxplode or something. Throws a door at me? Well, it is kinda stupid But, here's a real life example. When am I ever gonna find myself in a gym, and some beefy, bodybuilder I mean, this was a really stupid example. And, you can clean things up if you want. Of the amount I scream times, these two factors. Because the frequency should get increased by this Doppler Shift. And I know that I should be getting a larger total amountįor the frequency I hear. Dividing by a smaller denominator gives me a larger total amount. I wanna subtract because subtracting gives me a smaller denominator. The Doppler Shift should increase the frequency that I hear. So again, speaker, thisĭoor moving toward me. Memorizing is the fact that if things come toward each other, the frequency should be increasing. And on the bottom it's speed of sound plus or minus the speed That factor, if you remember, speed of sound on top. ![]() I need to multiply this by another factor that takes into account, the fact that the speaker- this door's not a speaker, but it's acting as a moving This was the frequency right here, f-door. Remember, this was the frequency, the door was receiving. The frequency I hear will be the frequency the speaker What frequency will I actually hear? Alright, we gotta doĪnother Doppler Shift. So I wanna know the frequency that I will actually hear. This door is observing, experiencing a higher frequency. We know what happens with moving speakers. This door is acting like a speaker, and it's acting a like moving speaker, because the door's moving. But no, because this is theįrequency the door hears. And then I should hear that frequency too. That's the way I remember whether I should add or subtract it here. I want the plus sign,īecause a big numerator gives me a larger frequency. So the frequency this door experiences should be bigger than the frequency that's actually emitted by If I'm moving toward the source, or if the source is moving toward me. So I ask myself this- I could never remember this as a student. Speed of sound up top, plus or minus for a moving observer. f-door is gonna equal the frequency that the wave actually has. And if we use the Doppler Effect formula. Because I wanna know what the door hears. ![]() Now, doors can't hear anything, but if this door was a person, what frequency would it hear? It wouldn't be f-scream. I wanna know what sound this door would hear if This door is gonna actĪs a moving observer. I'm gonna think of theĭoor as an observer first. So the frequency that I hear- I'm gonna have to do this I wanna know, what frequency would I hear? So I'm gonna have to use What sound would you hear,Īfter this sound wave reflected off the doorĪnd got back to you? Would you hear the same frequency that you're screaming at? Would you hear a higher frequency? Would you hear a lower frequency? Exactly what frequency would you hear? Let's figure it out, it's a This sound is gonna come over to here, it's gonna reflect off the door. And I'm going to call thatįrequency of the scream. I'm like, "Oh, no!" I start screaming at a certain frequency. You're looking at thisĭoor coming towards you. He doesn't know where he's throwing it, but he ends up throwing He's so mad, he takes theĭoor, he rips the door off. Because he's never wiping down his sweat off all the equipment. Because there's thisīig, beefy bodybuilder.
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