Into the sand, which it pushes around, causing erosion.
this post was submitted on 31 Aug 2025
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Also sound, you hear the splash.
Also some of it bounces back, this is the riptide that will carry you out to sea.
Yes but after? I get that it makes sound, pushes the sand and sends energy back to the open sea, by the energy that goes into the sand, where does it go afterward?
It dissipates into the environment through friction and other resistance forces. Each grain of sand is pressed against the others, the water, rock, or even the air. Those resistances are converted to heat and other forms of energy, which spread out from each particle.
Who says it has to go anywhere else? Why can't the energy just exist in the form of eroded sand and heat? If you use a huge amount of force to bend an iron girder (with apologies to Bender) where does that energy go? The iron girder doesn't inevitably spring back and give the energy back. It's just bent. But it also gets hot. That's where the energy goes.
Turning large grains of sand into smaller grains of sand uses energy, which becomes heat in the process. If you put the heat back in, you can eventually melt the sand back together, but this is not a lossless, perfectly reversible process, see: "entropy".
The remaining energy is converted into heat.
Are you thinking about Newton's laws like F=MA and wondering if the wave is moving the earth on some scale? You might have already answered yourself because for every action there's the equal and opposite reaction. The energy going into the sand is roughly equal in magnitude to the energy that got sent back into the sea. The waves and sand erosion you see are the manifestations of the energy bouncing around in this system as it finds homeostasis.
You're thinking of momentum, not energy. Momentum finds homeostasis, energy is dissipated as heat.
Heat, mostly. Some sound. Maybe it pushes something uphill (potential energy), or breaks something (chemical energy on the new exposed facet). Or, maybe not. In general, if you ever don't know where the energy went, it's probably heat.
To be more exact, the water hits a thing, and bounces off into eddy currents, which in turn split into ever smaller eddy currents. Eventually, the viscosity of the water is significant in comparison to the momentum of each eddy, and that slows it down. Viscosity is when organised movements of molecules dissipate, through collisions, into random movements, aka heat.
I guess I should mention that if it's not too rocky and uneven of a shore, waves will also bounce off back into the sea. This is only assuming it's absorbed.
That's the answer I was looking for! I don't imagine there is a way of measuring the heat produced?
Ultimately, it turns into heat, so that isn't wrong. But If it were immediately converted to heat as it crashed into shore, the shorelines would be boiling. Most of the "heat" is in the form of moving air in the atmosphere as the wave passes below it, and most of that heat radiates into space.
Most of the energy that crashes onto the beach ends up going back into the sea as a reflected wave.
This is an old lecture on the properties of waves. Pay attention to the types of reflection.
Polynesian "Wayfinding" relied heavily on understanding how waves reflect off shorelines, enabling navigators to locate islands beyond the horizon.
(You'll find that the shallow water is much, much warmer than the deep water at the beach, but I always blamed the sun for that.)
That is true.
That temperature difference is also true in the middle of the ocean, far away from any beach for a wave to crash.
Blame for the temperature delta you have identified rests with insolation.
Maybe there's still a delta, but when the water is a metre or two deep it's barely noticeable, whereas it's really really stark between a foot and two inches depth.
Yeah. I felt like the spirit of the question was about how moving water can rapidly stop without breaking energy conservation, so I focused the answer there. I did mention reflection back into the sea at the end.
But If it were immediately converted to heat as it crashed into shore, the shorelines would be boiling.
How do you mean? Waves carry significant energy, but moving water carries even more significant cooling capacity.
Dam spillways are designed to dissipate the full power capacity of the dam with splashing, and there are modifications made to some shorelines to increase the amount of absorption of incoming waves, specifically.
Yeah. I felt like the spirit of the question was about how moving water can rapidly stop without breaking energy conservation, so I focused the answer there. I did mention reflection back into the sea at the end.
My point is that the moving water doesn't "rapidly stop" when it hits the beach. The beach does not absorb very much of the energy of the wave at all.
As it arrives at the beach, the water flows uphill, against gravity, converting kinetic energy into potential energy, not heat, at least not in any significant quantities. Now the water is high up on the beach. Gravity drags it right back downhill. That energy travels back out to sea. Virtually all of the energy of the wave is reflected back into the sea. The proportion of the wave energy that is converted to heat/noise at the beach is a tiny fraction of the total wave energy.
The video I linked discusses mechanical wave energy absorbed by a "dashpot". The dashpot analogizes conversion to heat. If we were to model a beach, we would need to use an infinitesimally small dashpot.
Sure. I don't think we're disagreeing on much of any substance here.
The thing is that a little heat is equivalent to a lot of movement (which is basically the principle the whole industrial era was built on) and water has a really high heat capacity on top of it. The drop off of Niagara falls (Canadian side) translates to a bit more than 0.3C as a result.
Bolometers can detect pretty crazy tiny differences in temperature, so in principle you could measure it. It seems like it would be hard to distinguish pre and post-splash water in an ocean like context, though, and then there would be conduction happening within the water and between the water and the shore on top of it. Biological and chemical activity could also be confounding, and during the day so would the sun.
Into me, doing a cool martial arts montage.
You got proof to back up your claim bud?
Gestures broadly at the 80s.
Wax on, wax off
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