Ghoulish Delight
05-06-2010, 04:42 PM
I'm surprised we've never started a thread to discuss. I've tried to go to their message board in the past, but lordy my brain just does not operate on the right wavelength to handle a massively active board like that.
Anyone watch yesterday? Good episode, solid result on the car crash, but (as is often the case) I was left grumbling about how they summed things up and what they missed.
I wish they had done 1 more test case. Namely, one of the cars stationary (but free to move if impacted) and the other at 100MPH. The result should have been approximately the same as the 2 cars colliding at 50MPH each, and would correctly explain why Jamie had the 100MPG figure in his head.
And I'd also point out that, from a total energy in the system perspective, Jamie was not wrong about it being equivalent to 1 car at 100MPH running into a wall. It's just that with 2 cars, that energy is distributed so each absorbs about half, while, because the wall is essentially unmovable, the 100MPH car into a wall absorbs all of the energy.
I think that's an important point considering what the original test case that Jamie was talking about was. It was about crushing a car to flatness between the 2 trucks. And in that setup, yes, the car would have been subjected to approximately as much energy as is created when one runs into a wall at 100MPH.
I was also thinking about what Adam was saying, that he was having a hard time intuitively visualizing WHY the result was what it was. I figured out a good way to imagine the difference. The key mistake Jamie made was that, while combining the two velocities was correct, he replaced the mass of one of the cars with the mass of an immovable wall, thus changing the equation. If you want to picture why that mistake is significant, just picture the original case, with 2 cars coming at each other at 50 MPH...but replace one of the cars with a massive wall that wouldn't slow down on impact. I think we'd all have a pretty instinctive idea of what would happen, and why it's different than 2 cars.
Anyone watch yesterday? Good episode, solid result on the car crash, but (as is often the case) I was left grumbling about how they summed things up and what they missed.
I wish they had done 1 more test case. Namely, one of the cars stationary (but free to move if impacted) and the other at 100MPH. The result should have been approximately the same as the 2 cars colliding at 50MPH each, and would correctly explain why Jamie had the 100MPG figure in his head.
And I'd also point out that, from a total energy in the system perspective, Jamie was not wrong about it being equivalent to 1 car at 100MPH running into a wall. It's just that with 2 cars, that energy is distributed so each absorbs about half, while, because the wall is essentially unmovable, the 100MPH car into a wall absorbs all of the energy.
I think that's an important point considering what the original test case that Jamie was talking about was. It was about crushing a car to flatness between the 2 trucks. And in that setup, yes, the car would have been subjected to approximately as much energy as is created when one runs into a wall at 100MPH.
I was also thinking about what Adam was saying, that he was having a hard time intuitively visualizing WHY the result was what it was. I figured out a good way to imagine the difference. The key mistake Jamie made was that, while combining the two velocities was correct, he replaced the mass of one of the cars with the mass of an immovable wall, thus changing the equation. If you want to picture why that mistake is significant, just picture the original case, with 2 cars coming at each other at 50 MPH...but replace one of the cars with a massive wall that wouldn't slow down on impact. I think we'd all have a pretty instinctive idea of what would happen, and why it's different than 2 cars.