It happened that I was having my coffee and saw this video at the same time. It's an interview given by RP.Feynamn. In that Feynman explains about why is a cup containing coffee hot, he says that as coffee is hot the kinetic energy of atoms in coffee are transferred to that of cup and hence it gets hot too!

The answer was satisfying to me but something bothered me after a while.

If atoms in the cup are in motion then why don't I feel the jiggling of those atoms?

The possible answer that I think is that the kinetic energy isn't enough to feel. For instance instead of putting hot coffee and heating the cup let's heat the cup on a flame. Then it's obvious that it will break after a while which is exactly what happens if the atoms starts much jiggling.

My question:-

$(1)$- Is my explanation to it correct?

  • 9
    $\begingroup$ You do feel it when you touch a cup of hot coffee and it feels hot. Can you clarify what you are expecting to feel? $\endgroup$
    – DanDan面
    Feb 8, 2022 at 5:05
  • $\begingroup$ @DanDan0101, I was actually talking about sensation of movement of atoms inside of cup. $\endgroup$
    – RAHUL
    Feb 8, 2022 at 14:17
  • 1
    $\begingroup$ You ARE feeling the sensation of movement of atoms... that is what your brain processes as "heat" $\endgroup$ Feb 8, 2022 at 15:24

1 Answer 1


The motion of the molecules and atoms in the hot coffee cup have amplitudes of vibration which are far, far too small to detect with your fingers. Note also that on a macroscopic average, there is no net motion of the cup's surface on length scales of order ~fingertip width because for every single atom stretching its bonds in the (x,y,z) direction there will be another atom stretching its bonds in the (-x,-y,-z) direction. So you feel the temperature of the cup with the thermally-sensitive nerve endings under your skin but you cannot feel the vibrations of the individual atoms and molecules themselves.


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