I mean like mugs full of hot water and stuff like that.
I undestand they don’t actually get any hotter than they already are, so why does it feel like that?
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The thermal receptors in your fingers measure their own temperature, just like a thermometer. When you’re touching an object like a mug, which conducts heat poorly, it takes time for the heat to make its way out of the mug and to the receptors in your fingers, meaning you sense it rising slowly because it *is* rising slowly. If you touch a piece of aluminium at the same temperature you’ll get burned instantly because the heat transfer happens much faster.
Tempurature is very slow. As opposed to pressure for instance. Because the heat is traveling deeper and closer to nerves.
Five year old: So, if you hold something hot like a potato for a long time, your hand feels like it’s getting even hotter, even if the potato stays the same hotness. It’s because your hand keeps telling your brain, “It’s getting hotter!” the longer you hold it. Your hand starts off at 98° and the potato at 200°. It will take time for your hand to warm up and continue telling your receptors, hot hot hot!!! Before you throw it to your sister.
You don’t sense *things*; you sense *changes* in things.
So: you don’t feel temperature; you feel changes in temperature. The longer you hold it, the more and more the temperature of your fingers is *changing.*
Whatever you are holding is hotter than your skin. Nature doesn’t like things in contact to be at different temperatures so heat transfers from the hotter object to the colder one.
This means that your skin gets hotter and hotter the longer it’s in contact with the object. This is the ‘extra’ heat you’re feeling.
The heat is slowly transferring to your body so the longer you hold it, the more thermal energy that is in your hand hence more heat / pain
An interesting “experiment” that you can run yourself. You have perhaps seen videos of were (idiots) put a torch directly to a big log, or a 4″x4″, and it wont catch fire. And they say “so how come notre dame could burn down??”
Well, the thing is its nearly impossible to get a log to catch fire that way. But if you put two logs together, making a corner, and then apply heat, it will catch fire. Its the same effect, corner A will heat up corner B more and more, until we reach ignition.
Different objects have different heat properties, thats why ie. the cheese on the pizza seems to be 50 degrees hotter than the rest of the pizza. No, the cheese is exactly the same temperature, but because of its psychical properties, it can deliver that heat a hell of a lot quicker than Ie bread. Water is an excellent thermo-source, so a hot cup of tea, will deliver “all of its heat” quicker than a cup of hot sand.
Because more energy has transferred to you, more energy = more hot.
If I recall correctly from chemistry class: heat is a byproduct of energy transfer. And yeah, the longer you make contact with a hot surface, the more time that energy has to transfer to seek equilibrium with it’s surroundings.
On the opposite end of the spectrum here, you can also cold soak an object. Pilots have gotten in to trouble flying in to rain, after being at a below freezing altitude for a while, even if ambient temperatures in the rainstorm are above freezing by a surprising margin. Their cold soaked aircraft makes contact with the rain, which then freezes to the airframe and ruins the shape of the airfoil which normally produces lift, but now the shape doesn’t produce lift AND the aircraft gathers weight really quickly as it collects ice.
We all know objects are made up of atoms and molecules. These atoms and molecules constantly move around or ‘jiggle’ inside and on the surface of the object. This ‘jiggling’ decides the energy or the ‘excitement’ of the object.
When we say an object is cold, it means atoms and molecules are stable and are not jiggling. Hence, water turns solid when it gets cold. On the other hand, when an object is hot, it means these atoms and molecules are really excited and are ‘jiggling’ a lot. The higher the temperature of the object, the faster it’s atoms jiggle or vibrate.
So how does heat transfer take place? Let’s say I bring a vibrating ball in contact with another stationary ball (both balls are fixed in place and are not free to move, just can vibrate). The vibrating ball is going to keep hitting the stationary ball and transfer its energy so both balls start vibrating.
Similarly, let’s say I place a ice cube on a hot pan. The atoms of the pan are vibrating intensely, and these atoms keep hitting (literally) the more or less stationary atoms of the ice cube resulting in the atoms of the ice cube to start vibrating. This is what you will see if you use a powerful microscope to observe heat transfer. It is literally the transfer of mechanical energy (or physical movement energy) from one body to another.
When you touch a hot object, the atoms of the object keep hitting your cells with extremely high intensity. Imagine thousands of hammers hitting each cell really hard and extremely fast. This hammering damages our cells which is what we call a burn.
To answer your question, since hot objects literally hammer your cells, you will start to feel more painful the longer you hold them. Of course this is true for moderately hot object. Boiling water is so hot that the hammering effect is extremely strong and it can instantly burn you.
Hope this answers your question.
Edit: Credits to Richard Feynman for this amazing explanation of heat transfer.
The mug itself is getting hotter. The liquid inside is getting cooler. This will continue to happen until they reach an equilibrium.
It takes time for heat to travel from hot mug to your hand. The speed of heat travel varies by material.
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