Ok if some idiot in a truck hauling a huge pile of tires in the bed was speeding down the expressway at say, 75mph, and one of those big 'ole tires fell out, shouldn’t the tire roll forward? The truck was going forward so why did the tire roll down the road and almost hit all those cars. Man this was funny. Too bad I was going the opposite direction. It would have been fun to dodge those tires!! There just aren’t enough obsticles on the streets these days…
Anyway, so what gives? Why would a tire go the opposite direction of the truck it was in??
It’s probably because of the airflow over the truck.
The truck’s moving, the air isn’t. The tire gets caught by the air, friction accelerates the tire in the effective direction of the air. Nominally it might be immobile, but the truck causes the air to first move out of the way then flow back into the space behind the truck. So the air is moving pretty fast down and back. So the tire gets accelerated backwards.
Just a question–are you sure the tire actually went backwards? Could it have just been slowed down some but still moving forward–but not relative to the truck andother cars? Just curious…
Nope… definitely moving backwards. It was spinning clockwise (from my perspective) and everything. Which means it was moving in the same direction as me. The truck was going North, the tire and I were both going South.
How 'bout kinetic friction? The tire could have moved forward at a pace slow enough to only make it appear as though it was moving backwards. And then there are vectors to consider. I don’t know what they are. But I’m sure they are there. And perhaps the force that displaced the tire from the truck was greater than the velocity with which the truck was moving. I don’t know.
But I do agree that we need more obstacles on the road. That’s for sure.
I just realized that if you really wanted to dodge the tire, you should have jumped the highway median, crossed over to the other side, spun a 180 to face the tire, then punched the gas. So essentially, it’s your fault. Shame on you and your lack of resolve.
THis is true… and normally I would have turned around and caught up with him to stop the wacko for safety concerns. Those things could kill someone. But I was on my way to work. I did call the sheriff’s office from my car and let them deal with it.
My guess: Something (wind, maybe?) caused the tire to stop relative to the road, or at least slow down. Since it’s still on the flatbed at this time, it’s rolling, clockwise as seen from you in the opposite lane. When it hits the road, it’s still got that angular momentum, so it starts rolling on the road, causing it to move backwards. It’s sort of like that trick where you throw a basketball a little ways in front of you and get it to bounce back to you.