“Temperature Rise due to Slapping”
Courtesy of The 6th Edition of Thermodynamics, An Engineering Approach
Due to a recently receiving a slap-in-the face (not intentionally!), I’d like to turn this negative scenario into a perfect resource to study for my upcoming midterm.
Assumptions:
1. The hand is brought to a complete stop after the impact.
2. The face takes the blow without significant movement.
3. No heat is transferred from the affected area to the surroundings, thus the process is adiabatic.
4. No work is done on or by the system, and PE=0.
Energy conservation equation~ delt E=delt U (face)+delt KE (hand)
Now, let’s analyze this incident in a professional manner without involving any emotions. Follow me as we explore deeper:
System: Opponent’s hand and my face
Process: Starting from contact of slap
Given values:
Temperature of face rises: 1.8 Celcius
Face tissue affected: 0.15 kg
Opponent’s hand: 1.2 kg
Specific Heat of face tissue: 3.8 kJ/kg*C
1. Closed system, no mass transfer (thank goodness!)
2. Kinetic energy decreases during process (Final velocity=Vf=0)
3. delt U=Internal energy=m*c*(delt T),
4. delt KE=[(Vf-Vi)^2]/2
5. Apply energy conservation equation and plug in values
6. Initial impact velocity of hand is 41.4 m/s!!!
