This force will cause the cart to accelerate—in this case, to the left, or the opposite way it was heading, which is why it slows down during impact and even reverses direction. But what is the ...

I'm reading Randall Munroe's book How To: Absurd Scientific Advice for Common Real-World Problems. I probably don't have to tell you this, but it's awesome (as is everything from Randall Munroe, the ...