You did indeed waste energy, and it did indeed turn into heat, but that heat was dissipated in a large enough system that the heat was difficult to measure. In more extreme situations that are nonetheless analogous, you can measure it: Throw a rock from orbit, and it will get very, very hot.
When the OP mentioned a box, in a formal sense what he was doing is defining a system. When I followed up by assuming the box is perfectly insulated and completely opaque, I was defining the system as closed except for our presumably external source of electricity in order to better illustrate conservation of energy.
To clarify, one set of scenarios I did not address was if work was done. If the motor was initially off, for example, and then started spinning, then the kinetic energy it gained did not become heat. In a real system, it eventually will, due to friction, but some portion of the energy in the system remains kinetic as long it is spinning. Similar applies to raising objects to height, to fields such as from an electromagnet, and to chemical reactions.
The last one is a good one to mention for this forum: if we were charging a battery in our theoretical box, even though perfectly insulated and opaque, we actually would not see as much heat, because most of the energy is stored as chemical potential. On the other hand, if we wait long enough, the battery will self-discharge, and there’s our heat again.
In our simple example (no change in potential energy) mechanical energy is kinetic energy.
The energy stored in moving part with mass like motors, this is not a lot and still ends up as heat.
As soon as you turn the power off the ‘mechanical init’ will soon stop having turned its kinetic energy to heat.
Lets take your free moving motor shaft example.
Most of the energy will be wasted as heat within the motor,
still, the rotating shaft itself will heat the air around it a little bit.
The mechanical energy of this system once we turn the power off is the 1-2 seconds it will take for it to stop, and this will become heat as well.
it will get hot, but not from energy you spend throwing it, but from friction with air. and falling due to gravity.
rock thrown by hand will not get hot enough to even measure, and when it falls it will get a bit hot due to impact, but still not much if you can even measure it. both of those thermal energies will be negligent compared to energy you spend throwing it. heat is not the only form of energy that can be wasted. there are dozen or so forms of energies.
Think of how the energy (joules) or power (energy per unit time = joules/s = watts) is used and when you add up all the components, energy is conserved or all accounted for. (Strictly speaking, mass-energy is conserved, but I digress. Energy conservation is enough here.)
Incandescent bulbs produce around 10 lumens per watt, and the rest of the energy/power is wasted as heat. But those 10 lumens per watt are energy converted to photons (light) most of which presumably escape the aquarium so you won’t get the full input power converted to heat. LEDs are roughly 100-200 lumens per watt. They generate heat too, but a lot more of the energy is converted to photons.
Compare the initial energy/power provided into the system with all of the energy outputs and conversions, such as light/heat/chemical/sound/potential/mechanical energy. The two sides of the equation, or the inputs and outputs, must equal (again barring mass-energy conversions like nuclear reactions). So you see, heat is just one of the possible outputs.
Put another way, if the full input energy is converted to heat, there must be no other form of energy to account for, otherwise you’re getting more output energy than you put in. If so, you’re due for a Nobel prize.
Those saying “yes” might be thinking about how there are almost always “frictional” losses of energy to heat with each conversion of energy. Loosely speaking, all those losses eventually result in the presumed “”heat death”:https://en.wikipedia.org/wiki/Heat_death_of_the_universe” of the universe, leaving no energy available to do work. While that may be our eventual fate on a universal scale, that’s not what is happening in these isolated examples.
A specific device will have a specific purpose. Produce motion, light, chemical bonding/storage.
The rest, we call that losses, will be heat. The useful part of the energy won’t always be heat.
You don’t start your engine just to heat up your garage, won’t you.
And the gas stove will have losses via the vapors that go through the chimney.
And the chemical bonding in the little thermo bags will keep the heat in till you break the metal.
In theory, all rain water will flow down from your roof.
And in theory, all energy will be reduced to heat, the “lowest” form of energy.
But in practical life as we know it, not always. At least not while we are waiting for it.
i don’t think it works this way, a hanging rock has a potential energy, a still electric motor does not, why? you let go of the rock, it falls, and gains speed due to gravity. it will create energy by falling freely, a motor otoh, will not start spinning until you put energy in it, potential energy of the rock is equal to it’s weight and height it is on, the motor you need to spend electric potential to get it working. unless you throw a motor, then it follows same laws as a falling rock.
One has a 10W heating coil
One has a 10W electromagnet (with no moving parts obviously)
Which one do you think will melt the ice quicker? after the ice melts will they both heat the water to the same temperature, given infinite amount of time? Where does thermal resistance comes to play?
Technically it does have a load: it’s own weight, magnetic pull, internal and external friction, otherwise it would spin forever.
i never tried to melt ice with electromagnet, but i have many maglocks at work, they are active 24/7, only when someone enters, they are demagnetized for 10-15 sec, or so, they are 500lb pull magnets, if you touch them they will be barely warm. i would think a heating coil would melt ice much much faster, in a magnet heat is a byproduct, magnetic field is their primary energy. which is not making much heat.
i just looked any my maglocks specks, they are 500ma at 12v, basically 6W consumption, that isn’t much at all, an xml makes about as much heat at full power.
That’s initially true in many use cases, but in a completely closed system those other forms of energy (electromagnetic radiation, kinetic energy) would eventually end up as thermal energy.
For light, that could be through absorption into an object, raising its temperature. For movement, that could be through collisions with other objects, or the air around the object.