Mechanical Waves Transmit Energy

[justadream]

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Mechanical waves transport only energy (not matter).

This begs the question: are they other types of waves that do transport matter?

 

[Cawolf]

I am relatively sure that by definition a wave transfers energy and not matter.

 

[justadream]

@Cawolf

Okay that makes it easy. I wasn't too sure since many places emphasize the "mechanical" word (why not just delete it !?)

 

[Cawolf]

Well mechanical waves and EM waves are different.

Mechanical implies that they require matter to propagate (air, water, etc).

EM waves travel through space and carry momentum (but not matter!).

 

[justadream]

@Cawolf
How do EM waves carry momentum without matter?

momentum = mv

m =0?
v = c

 

[techfan]

That's a quantum question. p=h/λ
h is Planck's constant (6.62606957(29)×10−34 J*s)
λ is wavelength
p is momentum

 

[justadream]

@techfan

Thanks for that.

I've never seen that in any prep book (TBR, TPR).

 

[techfan]

That was something I learned in my quantum class lol

 

[The Brown Knight]

@techfan

Thanks for that.

I've never seen that in any prep book (TBR, TPR).

Combine p = mc and E = mc^2 and E = hf.

 

[justadream]

Combine p = mc and E = mc^2 and E = hf.

Whoa! Mind = blown.

I thought E = mc^2 only applied to nuclear binding energy stuff.

 

[Cawolf]

They nailed it - quantum theory shows that EM waves carry momentum that is proportional to the inverse of the wavelength! 🙂