# does a rocking kettle cause the water to boil more slowly?

When I boil water in the kettle on my electric stove, sometimes it rocks back and forth making an annoying sound at a frequency of about 6Hz. When that happens, I move the kettle slightly to make it stop rocking. It occurred to me that although my motivation is to stop the annoying sound, it might also make the water boil slightly faster because the energy that had been wasted in maintaining the oscillation of the kettle is now being directed elsewhere. I am supposing that this energy is transferred to the kettle because the bottom of it is now in more constant contact with the electric heating element.

To test this theory, I am thinking that I could experiment by boiling the water each morning (as I already do) and note the time it takes to boil, the ambient temperature and the temperature of the water, and make sure that the exact same amount of water is in the kettle each morning. By noting whether the kettle vibrates or not, but without adjusting it, I could see if I can statistically disprove the null hypothesis that there is no correlation between the kettle boiling and the time it takes to boil.

Is there anything missing from the proposed design of the experiment, and/or is the answer already well known?

• It's almost certainly true that the more constant contact with the coils will make heat transfer a bit more effective, although the amount of difference might be small. Certainly worth a try though. Jan 5, 2014 at 4:52
• It's possible that the sloshing will result in heat being transferred faster to the water so less is lost from radiation and convection. So many parameters, so few experiments. Feb 24, 2016 at 7:18
• The kinetic energy of the rocking is negligible. much more relevant factors are 1) how does the motion change the thermal contact and 2) are you mixing the water enough to increase the heating rate. The latter happens, in a nutshell, by exposing cooler parts of the water to the hot stove, and heat is transferred at a rate prop. to temperature difference. May 10, 2016 at 22:37
• Although the question was really intended to be more about the adequacy of the design of the experiment rather than asking for alternative theories, I appreciate the input. However, physics may have been set back to an incalculable degree by the fact that I have since purchased and use an electric teakettle now. I shall leave it to someone else to claim the Nobel Prize for completing this important work. May 11, 2016 at 1:36
• Nothing missing except the results. Sep 12, 2017 at 12:10

## 2 Answers

You need to define boiling more accurately. For nucleate boiling it will actually slow the process down as agitation mixes the system. For a full boil less rocking does decrease your energy loss due to sound but thats likely minimal. In reality the agitation will likely decrease the time to a full boil by both dispersing the nucleated regions increasing water to pot surface area and increasing the temperature differential between the stove and the water by increasing flow acroas the surface.

Again, what dumpsterDoofus said, it depends on a lot of variables.

To treat it classically,

suppose the bonds of the plastic of the kettle work under hook's law:

$F = -kx$

and $F_{k} = \mu_{k} F$ kinetic friction

with $F_{s} = \mu_{s} F$ static friction

and what proportion of this energy:

$W = \int F dx$ turns into sound and energy.

You'll probably find this is negligible.

• its like we're calculating the curvature of a spherical cow May 10, 2016 at 23:44