Alright Nerds... question time.
 

So, I’m sitting here with my Econ group and we're arguing about a scene in the movie "Gumball Rally."

The scene is, a Ferrari is trying to escape from the police by entering a car trailer on a freeway.

The trailer is moving 65 mph on the freeway. To enter the trailer, the Ferrari must climb to *75mph* to catch up to and enter the trailer.

The question is, when you enter the trailer at 75mph, are you still moving at 75mph? Do you have to go from 75mph to 0mph within the length of the trailer to avoid flying off the other end of the trailer?

Two conditions: The engine is engaged. The engine is disengaged.

Discuss.

I think it would do an insano burnout up the ramp and crash through the front of the trailer. I've always wondered how exactly this would work, just like when KITT used to drive into it's hauler.


IBtheplanetakesoff

I've got three seasons of Knight Rider on DVD I'm going to go watch the extra features. See if they say anything about it in there

My thoughts. The non-driven wheels are going to find their speed (stopped) on the ramp almost immediately, because with no forward inertia, they can be stopped easily; you're only slowing the rotational wight of those two wheels, not the whole car. At that point, you're basically going up the ramps at ~10 mph.

Now, with the engine engaged, as soon as you get the rear wheels hitting the ramp, they're trying to spin 75mph on a non-moving surface. You can see what happens if you spin up and RC car then drop the rear wheels on the ground....it'll stop almost immediately if you stop giving it gas. As long as you don't stay in the throttle, and declutch in a MT car as soon as the rear wheels hit, spin down after making it ontot he ramp, you'd be ok. Basically, even though the wheels are spinning, you can slow them really quickly without upsetting the car becuase the inertia of the car is effectively <10mph at that point, going up a hill.

If you watch the old Knight Rider shows, you'll see a little puff when the front wheels pop up on the ramp and spin down, and you'll see the rear wheels spin for aobut 5 revolutions as the guy lets it spin down (remember, automatic) and lets momentum ease the car up the ramp; then, it's just a little bit of gas to make it climb the ramp.

Picture riding a bike, and locking up the rear brake. Pretty easy to lock it up, and it regains whatever rolling veleocity as soon as you let off the brakes..same idea here. Becuase you're not fighting the weight of the car, it's not like going 75mph to 0, it's jsut some clever shifting to keep up with the rapid wheelspeed reduction. You're still doing 65mph when you're on the ramps, so the laws of physics are upheld.

Here's the way it works:

The truck is going 65. The car is going 75. The car's tires relative to the ground are gound 75. When the car hits the ramp the tires will have to slow from 75 to 10, relative to the ground/ramp their rolling on.

So, what you do is drive up behind the ramp closing at 10 mph. Just before you hit the ramp you push in the clutch (or shift to N). The car will hit the ramp and the tires will very quickly slow down to 10 mph, and the car should roll up the ramp (assuming 10 mph is fast enough to roll up the ramp).

Attempting to do this with the car powered means as soon as you hit the ramp, you'd have to slow the wheels from 75 to 10 before you hit the end of the truck. This probably wouldn't be all that hard to do... but things could get pretty squirely with the motor's inertia still spinning the wheels.

Edit: Aaron said it pretty well too.

So, when you enter the trailer you'll be moving 10mph inside of the trailer, correct? Not 75mph inside the trailer.

Also, pretend you kept WOT. Would you be excelling from 75mph in the trailer or 10 mph in the trailer?

To answer the first part of your question, it depends on your frame of reference. To an observer riding in the trailer (and the driver of the car) you'd be going 10mph or less. To an outside observer, you'd be going around 75mph (and as you apply the brakes slowing down to 65mph).

If you kept it WOT all the way up the ramps, you would probably stall the car. Part of the trick is letting off the throttle as you hit the ramps, so that's kind of a moot point.

Actually, now that I think of it... if you kept on the throttle as your drive wheels hit the ramps, you would probably stall the engine.

Keeping it WOT in that scenario is similar to rolling along at 10mph (1st gear, 1k rpm), pushing in the clutch, reving to 4k and putting the car in 5th gear and dropping the clutch. You'd stall the engine.

Actually, I'd bet flooring it would mean spinning the tires all the way up the ramp. Think of Aaron's example of dropping an RC car, except this time drop it while tossing it forward 10 mph. The tires would either slow to 10mph, or assuming enough power and rotational inertia, just light up.

Hmm, maybe. With enough power, since the tires are already spinning fast enough to propel the car 75mph, I could buy that.

My guts still thinking it would stall because the tire speed would have to reduce to 10mph, and in 5th gear (or whatever necessary gear to reach 75mph) that would cause a stall. You can't do 10mph in 5th.

But, you may be right, I'm not considering that the tires are already spinning at the RPM necessary for 75mph.

I agree with both of you. However, you'll need a LOT of power (low end torque) to start spinning the tires once you hit the ramp.

The rest of my group said that you'll retain 75mph once you hit/enter the trailer.

The rest of your group doesn't understand basic physics as they pertain to momentum and intertia, as well as relative speed.

Then again, Im an asshole, we all have our faults. :D

Well, to the outside world the car would still be moving at 75mph for a little bit. The car will be moving at 65mph when the car is stopped too. Hell, from the right frame of reference, its also going over 1000 miles an hour. Or even ~6,800 mph.

On thing is for certain, it would not go 140mph (75mph + 65mph) when it hit the ramps.

THANK YOU!!! I need to print this stuff out. We argued for ~an hour.

Somebody get a trailer.
I'll go get a TransAm.

Scott, go get your trailer, lets try this out!

^word! We'll put it on break.com.

Ok. We're still debating about this. How I think we're going to solve it is when I go to Tokyo this winter, I'm going to ride a suitcase or cart onto a moving walkway in the airport and see what happens. I'll be sure to post the video :D

Nope. Thats not going to work on that side of the globe. The asian physics are very different from normal physics. Have you ever seen Crouching Tiger, Hidden Dragon? Chinese people (and I assume Japanese people too) can fly.

The Japanese bounce. They do not fly. There is a "Sea of Japan" effect that happens when you cross the ocean from Japan into China. I dont know much about it. It has something to do with trade winds or something...? Will this still affect my test?

If you where in a falling elevator, and jumped right before it hit the ground, what would happen? Considering the roof of the elevator didn't crush you.

You splatter slightly less far.

The real move is to swim up to the roof of the elevator and get outside of it and lay down. Use the elevator car as a big pillow to absorb the energy of the impact. That way you'll die a slow painful death from internal injuries instead of a quick one from a broken neck.

So what your tring to say is the person wouldn't be able to jump because they would be expiriencing a state of weightlessness... right?