I can't know for sure if this is a physics or biology question but when pressing against a hot object it feels hotter the harder I press. Any reason?


The figure below shows the cross section of the skin. Note that the nerve endings are between the dermis and epidermis layers. When you press your skin against a surface you compress the epidermis decreasing the thermal path between the surface of the skin and the nerve endings which are the thermal receptors that signal hot. This is essentially what @Aaron Stevens said.

For steady heat flow, the heat flow rate is proportional to the conductivity of the epidermis and the cross sectional area, and inversely proportional the the length of the path, for a given temperature difference. Compressing the skin decreases the path.

Bottom line, I think it feels hotter because compressing the epidermis increases the heat transfer rate from the surface contacted to the thermal receptors in the skin.

Hope this helps.

enter image description here

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It's probably due to the increased surface area of contact. As you press harder your skin deforms more and it covers more of the object. Since more surface area means more heat conductance it feels to be hotter.

It could also be due to decreased distance between your "heat receptors" and the object. A decreased distance means the heat reaches the "heat receptors" at a faster rate, and so the object appears to be hotter.

It comes down to any factor that quickens the time and raises amount of heat to diffuse to you.

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  • $\begingroup$ Thermoreceptors, located in the dermis. They are more concentrated in the face & ears than the hands (I think), so you might be able to test their importance in this phenomenon by comparing the sensation of pressing your hand hard against a hot surface to that of pressing your face with the same force against the same surface. $\endgroup$ – Rodney Dunning Apr 6 '19 at 15:15
  • $\begingroup$ 1. Increased surface area would increase the amount of heat absorbed but the heat concentration would remain the same as it is equally distributed, right? $\endgroup$ – yolo Apr 6 '19 at 18:43
  • $\begingroup$ 2. If something is in contact with something, how can it get closer via pressure. How are we strong enough to overpass the distance between the atoms of the heat source and us $\endgroup$ – yolo Apr 6 '19 at 18:45
  • $\begingroup$ @yolo 1) I was supposing that perhaps a larger area of contact would add to the perception of a hotter object (this question is all about perception). 2) Your skin is not rigid. Pushing harder onto an object does cause more of you to be closer to the object. $\endgroup$ – BioPhysicist Apr 6 '19 at 19:41
  • $\begingroup$ Doesn't point 2 therefore also mean higher surface area? And while more skin does comes into contact, skin already in contact doesn't get closer. Right? $\endgroup$ – yolo Apr 6 '19 at 19:50

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