# Will a boiled egg or a raw egg stop rolling first?

If we roll a normal egg and a boiled egg at the same time on a floor

1) with friction

2) without friction

which one will come to stop first (if they will stop at all) and why?

Can anyone tell me reason for this?

The boiled egg wins hands down when there is friction. The internal degrees of freedom of the liquid in the raw egg will affect its rotational motion and increase its friction and absorb part of the energy into internal motion.

Two sliding eggs will retain the same velocity if there is no friction and initial rotation, they will not roll so it is a tie. If an initial rotation is given (lets think space) the boiled will go faster because the raw will be turning energy into heat due to the internal degrees of freedom.

Actually when growing up, we separated boiled from raw eggs by giving them a spin. The boiled ones spin nicely. The raw wobble and stop.

• a comment on separating boiled from raw eggs: before refrigeration became ubiquitous one used to boil eggs as a method of preservation for longer times( think canning).One could end with bowl of eggs on the kitchen counter and not be sure if it were the recently gathered ones or the ones to be eaten. – anna v Jan 8 '12 at 4:43
• If you consider the internal liquid to affect the rotational motion separately, then you wouldn't count it in the moment of inertia of the egg, right? So you'll start with a lower moment of inertia for the unboiled egg. – Yashas Feb 22 '17 at 15:18
• If there was no friction between the shell and the liquid inside, you wouldn't have counted it while calculating the moment of inertia because it does not affect the motion of the shell. If the liquid wouldn't move in sync with the shell, it would be unfair to consider it in the moment of inertia calculation of the egg. So you'd possibly start with a lower $I$? This is pretty confusing and complicated. – Yashas Feb 22 '17 at 15:24

The previous answer stated:

If an initial rotation is given (lets think space) the boiled will go faster because the raw will be turning energy into heat...

Besides energy, linear momentum must also be conserved in absence of friction or other external force. Internal changes in energy (e.g. from rotational energy to heat) cannot change the linear momentum. In other words, if there is no friction due to the surface on which the eggs are moving (or if they are moving in free space), both eggs would continue at exactly the same velocity as they started.

When rolling down the raw egg's moment of inertia changes reducing its rotational kinetic energy. This doesn't happen with the hard boiled egg; thus it rolls down faster.

## protected by Qmechanic♦Sep 23 '14 at 7:31

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