Like most people, I often look for more efficient ways to do things. Since heat is just another form of kinetic energy, is it possible to cook a chicken by hitting it?
I see a few ways this problem can be approached: multiple hits, or one hit.
Using multiple hits could be more realistic, however this approach gives time for the chicken to cool off in between hits. On the other hand, one hit will likely be well above the thresh hold of being humanly possible– otherwise we would be hearing stories of professional boxers cooking their lunches by punching it mercilessly.
First off, we need to determine just how much energy it takes to turn this:
A chicken must be heated to 75 degrees Celsius in order to be cooked and safe to eat. As chicken is roughly 75% water and since water has the highest heat capacity of any common substance, we will use this to determine how much energy it will take to heat up our chicken.
To calculate the amount of energy it will take to heat a certain amount we use the following formula:
The specific heat of water is 4,184 Joules/Kg*degC
The weight of a full size chicken is 1.6kg-2.2kg
Assuming the chicken has been thawed, it will be at room temperature (20 degrees Celsius). This gives us a change in temperature of 75-20=55 degrees Celsius.
If we put these values into our formula we get:
Q=460,240 Joules -or- 460kJ
A study of top Olympic boxers revealed that they can punch with between 500-1000 Joules of energy. This means that our chicken would require between 460-920 punches to reach a temperature where it would be safe to eat. Although some of the boxers can hit pretty quickly, I doubt any of them could hit at a faster rate than the chicken would lose heat.
A person’s arm’s mass is around 5.3% of the person’s total weight. This gives us a mass of ~5.0kg. To deliver 460kJ of energy in one hit, our arm and fist must be travelling 430m/s or 1540km/h. This scenario seems even less likely than our first one!
Given that neither of these scenarios are likely I will add a third method.
Heat by friction
The bird with the highest top speed is the peregrine falcon. It can reach speeds of 390km/h! Using this as a baseline for the terminal velocity of a chicken, we can see if hitting the ground could cook a chicken.
The formula for kinetic energy is: KE= 1/2mV^2
Since our kinetic energy is being converted to heat, we can say that KE=Q and 1/2mV^2=cmT. We can solve this equation for Temperature and enter our known values:
T=1.4 deg C.
At a terminal velocity collision with the ground our chicken’s temperature will raise by only 1.4 degrees Celsius.
This is far from the 55 degree temperature increase we need to be able to eat it.
However there is a solution! When an object reaches terminal velocity, the friction with the air equals the pull of gravity downwards. Since air resistance increases with speed, the object cannot go any faster. However, the energy must go somewhere and is converted into heat!
Using this, we can say that the “energy” that an object would gain as it falls is converted directly into heat. This allows us to use the formula for potential energy (PE=mgh; m=mass, g=gravity, h=height) and substitute potential energy with the amount of heat energy we need (460 kJ).
There we go! If you drop a chicken from 23km in the air, by the time it hits the ground it will be fully cooked!
While it appears that there are three possible ways of cooking a chicken with kinetic energy, I am skeptical that any of them will work. But! Let me know if you plan on testing any of them– I would really like to witness a chicken colliding with the ground at terminal velocity.
You may get a cooked chicken, however I would venture to guess it wouldn’t be more than mush by the time you are done with it. It certainly won’t be more efficient than using an oven.
Nathan Van Rumpt