I'm having a toy physics problem with a stick of butter sliding down a metal roof.
I know that the heat affects the friction between the butter stick and the roof. Therefore it affects the speed of the butter stick.
However, is there anything else, such as heat itself that could reasonably (or noticeably) affect the speed of an object (or, in this case, a butter stick).
The viscosity of the molten butter lubricating the interface should decrease with rising temperature reducing the friction with the roof thus increasing the speed. This is similar to the gear oil lubrication in a car. The speed argument should hold for a large block of butter where the melting removes only relatively little of the total weight. A small piece of butter might lose so much weight that it eventually stops moving.
When you apply heat to a system the atoms start vibrating faster because you're imparting energy to the system. Now, yes heat did increase the speed of the vibration of atoms in the sample but it didn't cause the sample to move.
In the butter and knife situation when you heat the knife the butter on that part melts and that fluid form is less viscous than the hardened butter. Butter in form of fluid on the contact surface is what increased the speed of the butter's movement. Heat did cause it to happen but the main reason for the "speed" increasing was melting.
In a similar way if you consider a metal ring that is free to move on a metal rod, initially it slides smoothly. But if you apply heat the ring and the rod expand, causing the ring to "fit" tightly around the rod and hence restricts movement.
I hope I've satisfied your curiosity :)
