Answer:
it's A endothermic its when two objects rub each other to form heat this is also known as friction force
The pH value can be measured using electrochemical measuring systems, litmus paper, or indicators and colorimeters. The easiest way to take a pH measurement is to use litmus paper or a colorimeter. The advantage of this type of pH measurement is that the pH range is well known and they are easy to apply.
I think its the brain or muscles... sorry if im wrong .