# Mechanical Energy Absorption

I’m in the process of creating an organism on a planet that has the ability to absorb mechanical energy directed at it and convert it into heat with a very high efficiency rate of over 70% only to dispel that heat later through other biological processes and I wanted to ask if there was any way to explain this scientifically?

Just for reference this organism shouldn’t really take damage from an incoming bullet because upon impact the bullet should have transferred its mechanical energy but that energy would have transformed into heat energy only heating up the organism, not piercing it (Given that the incoming bullet doesn’t deliver an energy level past the organism’s threshold)

(Just for clarification I would think its similar to the law to the conservation of momentum in the sense that this organism converts over 70% of the momentum that impacts it into stored heat while the other 30% is transferred to the organism.)

I would think an example of this would be a bullet being directly shot human per say in the skull and the bullet doesn’t pierce them but falls off to the ground while the human touches the area where they were shot and notices that the area has heated up and stings from the pain but hasn’t pierced them, (I apologize if this example isn’t very specific)

• Any organism, and anything at all, does that, with 100% efficiency. – MolbOrg Apr 11 at 22:28
• I think a clarification is needed. Are we talking about conservation of momentum, such that 70% of the momentum is converted to stored heat, and 30% of the momentum is either transferred to the organism or 'passes through' the organism? That is, is this organism a super-efficient (70%) shock absorber? – Justin Thyme the Second Apr 12 at 1:01
• It would be similar to 70% of the momentum being converted to heat and 30% being transferred to the organism and I apologize for not being specific. – user84821 Apr 13 at 14:37
• Momemtum is momemtum is momentum. It cannot be converted to heat, or to anything else, and it cannot be destroyed. – AlexP Apr 13 at 14:47
• @AlexP heat literally is momentum, atomic level vibrations. also, a pendulum in a vacuum naturally (eventually) will stop moving because it'll release all the momentum in the form of radiation due to the momentum being converted to heat and then radiation. – zackit Apr 13 at 19:11

Any inelastic collision would do that: take a bag full of sand or water, drop it on the ground, it will splat flat there. All the kinetic energy it had before the impact has turned into heat, with a 100% efficiency (when it comes to turning energy into heat thermodynamic is your friend).

If you want another example, see what happens if you fire a bullet into sand or water: all the bullet energy gets dissipated into friction and heat.

• The trick is recapturing heat energy as chemical energy that you can harness to make ATP The heat eaters; a biological Stirling engline. If there is a way to use heat to make ATP I do not know it. – Willk Apr 11 at 21:54
• @Willk there's thermosynthesis, which if i recall correctly uses the vibrations from heat to decompose molecules, and, when those molecules are reassembled, will release all the chemical energy so it can be used. Just convert the chemical energy from one reaction into chemical energy stored in ATP and you're good. – zackit Apr 13 at 19:15
• @zackit - yes thermosynthesis is the heat eater but it is still theoretical. AFAIK there are non candidate molecules that could undergo the needed conformational change and harnessable reassembly. I asked about exactly this on the chem stack: chemistry.stackexchange.com/questions/127162/… – Willk Apr 13 at 19:37

The kinetic energy of a standard 9mm bullet is in the region of 600J. An energy transfer efficiency of 70% to an organism of approximately 75% water would give an approximate temperature increase of 1 degree Celcius - assuming that your organism can distribute the thermal energy quickly and uniformly around its body. You would need to decide the temperature at which it would suffer harm just from temperature rises.

That would then leave 30% (180J) of mechanical energy. With a mass of 30g and an area of 6.4x10-5m2 then a bullet would still apply a pressure of approximately 735psi. Human skin will break at about 100 psi. Even a strong bone, like a femur, will break at about 160psi. You are going to need an organism that has thick scales and a thick compressible layer underneath or a jelly-like creature that can handle bullets riddling it and not be harmed.

• Thank you very much for your answer I very much appreciate it and even though this organism isn’t really Jelly-like I will take your answer into great consideration, Thank you – user84821 Apr 13 at 14:44
• I didn't think you would. You will need to either increase the efficiency of heat conversion - in which case watch out for local thermal damage - or come up with a plausible way of withstanding that pressure. – Hukk2010 Apr 13 at 15:32