Original Air Date: May 5, 2010
Aeon Cole – TwoCents Reviewer
In this week’s episode entitled Mythssion Control, the Mythbusters take on two redos at the fans’ request. This isn’t the first time the Mythbusters have gone back to revisit prior stories because of fan criticism or fan suggestions for improving a story.
Jamie and Adam take on something Jamie had said during the now infamous Compact Compact episode all the way back in Episode 41 while the build team performs a redo of Knock Your Socks Off from episode 125.
Five years ago the Mythbusters did an episode where they tried to smash a compact car between two semi trucks driving toward each other at 50 miles per hour. Jamie made the comment that that was like one truck hitting a wall at 100 miles per hour. Well this set off a storm of emails and posts to their message boards stating that this was not true and that Newtons 3rd law, “Every action has an equal and opposite reaction,” proved it. Never ones to turn down a challenge or admit that they might be wrong, Jamie and Adam set out to see whether or not the fans were right.
They begin with small scale tests before getting to the good stuff and smashing actual cars. Their small scale was done in a classic fashion with pendulums and clay. Anyone who has ever taken a physics course will recognize the setup. They determine a benchmark for the pendulum hitting a stationary object at a set speed and then twice that set speed by measuring how much the clay in the rig is compressed. There was clear difference. The 2x clay was compressed to roughly half the size of the 1x clay. Then they swung two pendulums so that they hit each other at the 1x speed to see how much the clay is compressed. This clay matched the 1x from the previous test. In the small scale they confirmed Newton.
The large scale test took the boys to a crash testing site in Arizona where they repeated their test with actual cars. They smashed two identical cars into a wall, one at 50 miles per hour and one at 100 miles per hour. Both cars were loaded with accelerometers and measured before and after the crash to establish a benchmark. Once again there was a clear difference between the two. In fact the 100 mph car was almost obliterated. The only thing left to do was to smash two cars together at 50 miles per hour. The two cars hit and Newton is vindicated. The damage to the cars is virtually identical to the 50 mph crash against the wall.
So why did Jamie make that mistake in the first place. Well, it’s an intuitive result. Each car is going at 50 mph so together when they hit you should add the speeds. The problem is that thinking this way you are confusing energy with force. The energy expended in the two car crash is twice that of the one car crash but it’s spread out over twice the area so the force is halved. Newton wins.
So, what were the fans’ complaints about Knock Your Socks Off? They said that the build team only used one type of punch, the upper cut. They also complained that the type of sock that was used was to elastic and clung to the legs. And finally, buster hadn’t been standing with his full weight on his feet. Tory also added that they should test the difference between hairy legs and smooth legs, something I’m sure he regretted later on.
Armed with all of these possible problems with the original test, the build team set off to address each one. Kari waxed one of Tory’s legs, amusing to watch by the way, and Grant built a robot to pull socks off of Tory’s legs to determine which slid off the easiest. After determining that a wool knit sock slid off the smoothest from the waxed leg they resumed their testing with Buster. They rigged Buster so that he would have his full weight of 180 pounds on his feet when the punches hit. First they tried the upper cut, then a right hook and then a body punch using the same robot punching device they had used originally but set to twice the power of a human punch. If this didn’t knock his socks off then a human punch never would. And it didn’t. You can’t knock someone’s socks off with a punch.
But, of course, they weren’t going to leave it there. They decided to see if there were any circumstances under which this myth was true. They rigged a flatbed truck with a metal bar welded to the rear sticking off to the side so that it would hit buster as it drove past him. On the second try they did actually manage to knock Buster out of his socks leading to another of those great shots on the high speed. You see Buster flying backwards and right out of his socks.
This was a fun episode which used some solid science to confirm this week’s myths. What did all of you think?