Knight Rider Moving Trailer Entry

Prior to "Baywatch", there was the 80's TV show Knight Rider, that starred David Hasselhoff as the iconic Michael Knight who fought crime with his partner, the talking super computerized sports car, KITT. Every episode had a chase scene, and the car would often enter or exit the back of a trailer via a ramp, while the trailer was moving at highway speed.


What I am wondering about is the physics of driving a car up a ramp into the back of a trailer while the trailer is moving at 50 miles per hour. The car must move in excess of 50 mph to close on the ramp. Therefore, when the rear tires hit the ramp (the car is a Pontiac Firebird), they are powering the car forward in excess of 50 mph. Won't the car suddenly accelerate forward when the rear tires move onto the relatively still ramp surface? I picture it like a car on a dynamometer when the cylinders suddenly stop.



If the ramp entry were really done at full speed, would the car going up the ramp suddenly accelerate into the trailer at 50 mph, or am I missing something?

They did it on Mythbusters, and the result was pretty much as expected.

Forget the show for a second, we know about things like acceleration. So if we have a wheel spinning very fast to maintain 50mph, and then it hits a surface that, relatively, is stationary, what do we think would happen?

If it's hard to picture, then picture this - put your car up on a jack. Get it up to 50mph. Drop the jack. What happens?

Hit "post" instead of "preview" =p

What happens is there is a bit of a skid... and nothing more.

I do wonder how much of this is physics and how much is situational. When driving at 50mph, you use very little of the skinny pedal. The amount you have the throttle open is about the same as you'd use to crawl into a trailer. So once the inertia of the spinning wheel is used up, you only have a bit of "power" actually in use.

I'd like to see them do it at full throttle. Though I can probably intuit what would happen there as well - you'd just peel out, same as if you were at a stop sign

I think next to the one on the correlation between breast size and tips, this is my favorite piece on Mythbusters. I've asked PhD scientists the question raised by this piece and so far they have all got it wrong.

There was an episode of Knight Rider where Michael went undercover as a stuntman and they made a big deal of jumping one truck and one car in front going like 30 or so. Of course KITT did it, but they said on the show FWTW that several "stunt driving legends died trying it."

This shows it would actually be hard.

Thanks for the info and the Mythbuster's video! Good stuff!

However, I am still not clear on the "why". Why does the car just roll up the ramp instead of burning rubber on it? Where does all the energy pushing the car 55 mph go? I suspect, as Face hypothesized, that the driver is "coasting" and not under engine power going up the ramp.

What is the 55 to 0 stopping distance for a late 80's Camaro?

Quote: Ayecarumba

However, I am still not clear on the "why". Why does the car just roll up the ramp instead of burning rubber on it? Where does all the energy pushing the car 55 mph go? I suspect, as Face hypothesized, that the driver is "coasting" and not under engine power going up the ramp.

Best as I can see is because the ramp is also going 55. Lets look at something easier to grasp. Ever go to an airport with a moving sidewalk? Even if you are at a jog, you do not go flying down the sidewalk. It takes you a moment to catch up with things.

Quote: Ayecarumba

However, I am still not clear on the "why". Why does the car just roll up the ramp instead of burning rubber on it?

Why doesn't Doc post here?

I'm sure there's a perfectly good mathematical explanation using lots of formulas I don't understand. So for a purely qualitative explanation all I can think of is this:

1) All speeds are relative.

2) If both the car and truck are going at the same speed relative to the road and the roadside scenery, then they're both motionless relative to each other.

3) This being the case, then the car needs to accelerate a little, relative to the truck's ramp, to actually climb inside the truck.

4) Ergo the car is moving only at 1mph or so relative to the truck.

Or let's turn it around:

Suppose the truck catches up to the car, both doing 55 mph, and touches the car's rear bumper (assume they're at the same height). In the car you'd barely feel the bump. If then the truck accelerates to 56 mph, it wouldn't throw the car forward at 101 mph.

Speaking of the Mythbusters, they did a related myth involving an open-bed pickup truck and a treadmill. Their insurer wouldn't let them try with a human being: http://www.discovery.com/tv-shows/mythbusters/videos/insurance-no-no/

They wound up shooting a ball out of an air canon mounted at the back of the truck..

I've asked PhD physicists, including my father, this question, and they always contradict the Mythbusters results.

The only explanation I can give, with only a recreational background in physics, is that the force of the moving car supersedes such things as relative motion. In other words, a body at a given velocity prefers to stay at that velocity.

Hopefully I can get Doc to visit us to chime in, but we had a thread on this at WoV some years ago and I think he will just refer us to whatever he said there.