• 0 Posts
  • 15 Comments
Joined 1 year ago
cake
Cake day: July 2nd, 2023

help-circle






  • Sooooo, wavelengths (λ) become longer when something moves away (redshift) and become shorter when something moves towards you (blueshift).

    For a red flag (λ0=610nm) to become a green flag (λ1=549nm), it has to move towards you quite fast. But how fast is ‘quite fast’?

    Using the formula

    flag_velocity / speed of light © = difference in wavelengths / starting wavelength

    we get

    flag_velocity = (610-549) / 610 * c = 61 / 610 * c = 1/10 * c

    This means: the flag has to move with about c/10 = 30 000 000 m/s = 108 000 000 km/h = 67 108 100 mph. Yeah, that’s quite fast.

    (Disclaimer:

    1. use info on own risk

    2. values for λ were chosen in a way to make calculations easy. There is no info on what shade of red or green the flag is. The final result will be about the same.

    3. With speeds at around 10% of c, I should use the formula considering the relativistic doppler effect… However, i wont. Thanks.)


  • Sooooo, wavelengths (λ) become longer when something moves away (redshift) and become shorter when something moves towards you (blueshift).

    For a red flag (λ0=610nm) to become a green flag (λ1=549nm), it has to move towards you quite fast. But how fast is ‘quite fast’?

    Using the formula

    flag_velocity / speed of light © = difference in wavelengths / starting wavelength

    we get

    flag_velocity = (610-549) / 610 * c = 61 / 610 * c = 1/10 * c

    This means: the flag has to move with about c/10 = 30 000 000 m/s = 108 000 000 km/h = 67 108 100 mph. Yeah, that’s quite fast.

    (Disclaimer:

    1. use info on own risk

    2. values for λ were chosen in a way to make calculations easy. There is no info on what shade of red or green the flag is. The final result will be about the same.

    3. With speeds at around 10% of c, I should use the formula considering the relativistic doppler effect… However, i wont. Thanks.)



  • The actual unit is lower case, the multiplier is uppercase.

    Wouldn’t agree with that… There are many different units and multipliers. the letter being uppercase or lowercase has nothing to do with it.

    Examples:

    letters for prefixes/multipliers being uppercase and lowercase: P, T, G, M, k, h, da, d, c, m, u, n (trillion, billion, million, thousand, hundred, ten, one tenth, one hundredth, one thousandth, one millionth, one billionth)

    Letters for units being uppercase and lowercase: s, m, g, N, W, J, A, K, V, h, Hz (seconds, meter, gram, Newton, Watt, Joule, Ampere, Kelvin, Volt, hour, Hertz) (just recognised, that most units, which are named after scientists, are written with capital letters…)

    km = thousand meters/kilometer

    K = Kelvin (unit for temperature)

    M = Mega (prefix for one million)

    kJ = thousand joules

    s = second

    ms = millisecond (one thousandth)

    S = siemens (electrical conductivity)

    mS = milli siemens

    mm = millimeter (one thousandth of a meter)

    Mm = megameter (one million meters or thousand kilometers)