Final answer:
The warmth felt when rubbing hands together is due to the friction between them, which converts work into thermal energy.
Chemical hand warmers also produce heat through exothermic reactions involving iron oxidation or other substances.
The efficiency of rubbing hands is low compared to involuntary shivering, which the body uses to generate heat efficiently.
Step-by-step explanation:
The force that makes your hands feel warm when you rub them together is due to the conversion of mechanical work into thermal energy. The warmth you feel is the result of friction between your hands. When a force is exerted over a distance, work is done, and in this case, the work is converted into heat energy due to friction.
To quantify this, if a person rubs their hands together with a certain force over a given distance, we can calculate the total work done using the formula Work = Force x Distance.
In a situation where a woman rubs her hands with an average frictional force of 40.0 N over a distance of 7.50 cm for 20 rubs, we calculate the total work done and then use the specific heat capacity of the tissues being warmed to determine the temperature increase.
Hand warmers represent another means of generating heat through chemical reactions. For instance, a typical chemical hand warmer works when iron and water within the packet react with oxygen in the air to form iron oxide in an exothermic reaction.
There are also hand warmers that utilize oxidation of lighter fluid, charcoal, or electrical heat generated by resistance in wires.
Lastly, it's worth noting that while rubbing hands together does produce heat, the process is not particularly efficient in terms of energy transfer to the outside world.
In contrast, shivering in response to cold is an involuntary bodily function where muscles rapidly contract to generate heat, which is a more efficient way for the body to produce warmth in response to a decrease in temperature.