# Tag Info

4

"Relativistic" velocities (velocities in excess of 0.1 c) are not needed. Any velocity difference will do. People use the doppler effect right here on Earth. Some sample uses: Catching speeders. How fast is his fastball? (Very important at this time of year.) Where is that tornado going?

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Your choice of the word "notice" is ill-defined. The Doppler effect holds true for all waves, at all speeds, so in that sense, you could "notice" the Doppler Effect for any wave you choose, no matter what the speed of the source or observer is (as long as there is some relative motion between the two.) Even as you walk across a room towards a lamp (to keep ...

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As you clearly ask for a detection criterion of the doppler shift on "a sample light wave", I have taken the liberty of assuming the following scenario. You detect light from a source, emitting light of a known wavelength (the usual case in astronomy for instance) with an instrument that is capable of measuring wavelength with an accuracy (i.e. with an ...

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It appears from your edit that you added the velocity of the ship and the speed of light classically. However, the velocity of the ship and the speed of light need to be added relativistically, using a Lorentz Transformation. Here's a quick way to know something is amiss with your moving ship: You state that the stern observer sees a wave propagation speed ...

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The speed of a photon, and all massless particles, is essentially always $c = 299792458\space m/s$. The Doppler effect is entirely contingent on the fact that the velocity is the same throughout. We have a source, $S$, emitting light at a certain speed: ...

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As stated in the comments: The Doppler shift is a change in observed frequency due to relative speed difference. However, the speed with which the signal propagates is the speed of light.

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The answer to this question is that if you can only see one line or feature in the spectrum then the redshift cannot be measured unless you have some other information that leads you to guess what the line or feature in the spectrum is due to (e.g. the 21cm line of hydrogen at radio wavelengths is so strong and ubiquitous it can usually be identified ...

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Sure. Your bike is slow compared to the speed of sound, so you can use the approximation for the Doppler effect for speeds that are slow compared to the speed of sound. Assuming your bike is moving directly toward the receiver, the equation for the Doppler effect can be expressed as $$v=\frac{c\ \Delta f}{f_0}\,$$ where $v$ is the speed of your bike, $c$ ...

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OK, I get your answer, but as this is a homework question and you have really not shown any attempt to get the solution I cannot show you it. The doppler equation you have is fine: I would write it as $\omega = \omega_{\rm star} \gamma (1-v)$ where we are using units with $c=1$. You then need to use a standard relationship between acceleration in the two ...

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Yes, gravitational waves will undergo the same red-shift as any wave that propagates at $c$. There were probably very violent gravitational waves in the very early universe. If those waves hadn't been red-shifted, they'd be ripping us apart right now. If so, could observations of them be used like red-shifted electromagnetic waves from distant sources ...

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