Bullet Impacts Crayons
How much energy is transferred from a bullet to a crayon during an impact? Does it pass with insignificant energy/speed loss? How many crayons should it take to completely stop a bullet? Very difficult to guess without some testing... A fun way to go about this is to fire a bullet through a series of crayons and determine the speed delta from before and after impact. Then, you could approximate the energy transfer during an impact by subtracting the bullet initial kinetic energy from its final kinetic energy (i.e., when the bullet is roughly through the crayon array). By definition, the KE = mv*v/2. The delta in energy came out to be 169 J, nearly a 40% loss in energy from 425 J! Based on this data, it would be interesting to see what people guess would be the total number of crayons needed to stop the bullet.
Please note that this test was conducted on a controlled ballistics range with all the necessary precautions to ensure the safety everybody who was involved. I do not encourage that anybody repeat this test in any other context.
This video was captured with the Phantom TMX at 76000 fps, 3 us exp, and 100 mm Zeiss makro. Enjoy.