Crave the Wave B

adatta0517
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Re: Crave the Wave B

Post by adatta0517 »

Source wrote:Waves traveling through a solid medium can be either transverse waves or longitudinal waves. Yet waves traveling through the bulk of a fluid (such as a liquid or a gas) are always longitudinal waves.

So I was reading about the categories of waves and I don’t understand how waves in water are longitudinal waves. I thought they’d be transverse waves, because if there’s a duck on the water, it bobs up and down, so isn’t the vibration perpendicular to the direction the wave is carrying the energy in the water?

Also, in transverse waves, I get that particle 1 is displaced, and that pulls particle two, which pulls particle 3, so on. But then how does particle 1 go back to its original position, for which the rest of the particles consecutively return back to its original position?

Also can someone answer @2above?
Last edited by adatta0517 on November 6th, 2021, 10:38 am, edited 1 time in total.
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Re: Crave the Wave B

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adatta0517 wrote: November 3rd, 2021, 4:37 am
knightmoves wrote: October 27th, 2021, 10:04 am
Alternatively, think about all the molecules individually, bouncing off each other. If you make an area of increased density, there are more molecules bouncing off each other in that space, and so statistically, they are likely to move away from the place where lots of molecules are and towards fairly empty places.
Can you explain this part more?
Imagine you've got a load of gas molecules bouncing off each other. Think of them as balls on a pool table, if you like. One end of the table has lots of balls, the other end of the table doesn't have many balls. All of the balls are moving. Now imagine you're a ball somewhere near the middle of the table. If you happen to be moving towards the end of the table with few balls, you'll probably keep moving that way, because there aren't any balls in your way. If you're moving the other way, there are a lot of balls there, and you'll probably bounce off one.

adatta0517 wrote: November 3rd, 2021, 4:37 am Here, the bat can simply just return back to its equilibrium position right? So that way, this one does require matter displacement but that matter just vibrates. (returns back to its original position after transferring energy to the ball) right?
Let's bring the pool table back.

Line up a row of pool balls in a straight line. Strike the cue ball square at the end of the row. The cue ball will stop, the row of pool balls will (mostly) not move, and the ball at the end of the line will move away. You've probably done the same thing with a Newton's cradle. So you can see how the energy moves through the row of balls without causing net movement of the balls.
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Re: Crave the Wave B

Post by aakoala »

hey guys! to anyone that has done invitational tests so far this season; how much of the test is math-based? I know a lot of density labs tests are heavily reliant on math, but the crave the wave rules seem more concept-based. Would you expect more than half the test to be math-based? thanks!
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Re: Crave the Wave B

Post by Adi1008 »

aakoala wrote: January 3rd, 2022, 9:27 am hey guys! to anyone that has done invitational tests so far this season; how much of the test is math-based? I know a lot of density labs tests are heavily reliant on math, but the crave the wave rules seem more concept-based. Would you expect more than half the test to be math-based? thanks!
Back when I competed in Crave the Wave (2014-2015), the exams were very math-heavy. Of course, test writing styles may have changed since then, so your experience might be a little different.
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Re: Crave the Wave B

Post by adatta0517 »

Hello. I had a question about the amplitude and whether it has to always be constant or not.

So how come the distance from the equilibrium to a crest is always equal to the distance between the equilibrium and the trough? Like let's say in the slinky example, we apply a certain amount of force to make a certain distance from the equilibrium to crest, but then we apply more force when moving it down, (that is, apply more force to make the distance between the equilibrium and trough bigger)? And then is it possible to have the next crest be just as far away from the equilibrium as the last crest, or is it that the more potential energy that was created for the trough will convert to more kinetic energy therefore making it go more up and therefore increasing the distance between the crest and equilibrium?

Thank you. :D
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Re: Crave the Wave B

Post by adatta0517 »

Bump.. can someone answer my question above?
Thank you!
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Re: Crave the Wave B

Post by gz839918 »

adatta0517 wrote: January 19th, 2022, 4:54 am Hello. I had a question about the amplitude and whether it has to always be constant or not.

So how come the distance from the equilibrium to a crest is always equal to the distance between the equilibrium and the trough? Like let's say in the slinky example, we apply a certain amount of force to make a certain distance from the equilibrium to crest, but then we apply more force when moving it down, (that is, apply more force to make the distance between the equilibrium and trough bigger)? And then is it possible to have the next crest be just as far away from the equilibrium as the last crest, or is it that the more potential energy that was created for the trough will convert to more kinetic energy therefore making it go more up and therefore increasing the distance between the crest and equilibrium?

Thank you. :D
Hi there! You're correct that the amplitude of a wave doesn't have to be constant over time—that's some good intuition on your part! For your third question, the energy that the system gains is equal to the energy that you put into it. You can explore this for yourself on this PhET wave simulator: https://phet.colorado.edu/en/simulation ... n-a-string. If you put in a greater driving force, then you'll see that the amplitude increases, and if you put in a smaller driving force, the amplitude may still increase, but not nearly as much (and if there's damping, which means that energy is being lost from the waves, the amplitude may even decrease if energy is lost faster than you put in). Hope that helps, and feel free to ask again if you have more great questions!
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