Bad Movie Physics Hurt Scientific Understanding

eldavojohn writes "A paper published by UCF researchers claims that bad movie physics hurt students' understanding of real world physics. From the article, "Some people really do believe a bus traveling 70 mph can clear a 50-foot gap in a freeway, as depicted in the movie Speed." The professors published this paper out of fear that society will pay the price. One of the authors commented on advancements in the past years "All the luxuries we have today, the modern conveniences, are a result of the science research that went on in the '60s during the space race. It didn't just happen. It took people doing hard science to do it." I commented on the physics of the most recent Die Hard having problems detracting from my enjoyment of the movie but is it really the root of a growing problem of poor science & math among students?"

Comments

Intuitor Insultingly Stupid Movie Physics

[imaginaryelf]

http://www.intuitor.com/moviephysics/

Re:Intuitor Insultingly Stupid Movie Physics

[king-manic]

Site was interesting, but sometimes comes across as nitpicky about things that really shouldn't be criticized, like the whole visible lasers or flashing bullet impacts - he doesn't really ask himself if it would make the movie any better if the lasers weren't visible or you couldn't see the impacts. Hell, you'd think the fact they're using hand-held laser weapons would be the bigger problem, if you can accept that why not visible lasers.

Hand held laser are a very real possibility and can do fairly high damage to dark targets with portable energy supplies. They'd function much like the "flashlights" in niven's known space books. With all the resultant limitations as well.

Re:Not yet? Really?

[litghost]

Well this comment shows the problem right away. This is actually a mass independent problem, as gravity is always accelerating things (on Earth) at ~9.81 m/s^2. The problem is more what the drag on the bus is over the course of the flight. However, since I am not in the mood to calculate Reynolds numbers for flying busses, I will assume inviscid air.

Problem statement: A point particle moving at 70 MPH at some angle must cross a 50 foot gap, and be at the same height when it reaches the other side.

Given:
v0 = 70 mph // Initial speed
x = 50 feet // Distance to travel horizontially

Assumption: Force-free motion
Constant gravity ( g = 9.81 m/s^2 )

Solution:

v0 = 70 mph = 31.2928 m/s
x = 50 feet = 15.24 m

t = Time of flight
theta = Angle from horizon

x = v0*t*cos(theta)
y = v0*sin(theta)*t - g*t^2
Solve for t t = x/(v0*cos(theta))
Substitude into y equation
y = x*v0/v0*sin(theta)/cos(theta) - g*x^2/v0^2/cos(theta)^2
Set y = 0 and solve
x*sin(theta)/cos(theta) = g*x^2/v0^2/cos(theta)^2
sin(theta)*cos(theta) = g*x/v0^2

g*x/v0^2 = 9.81*15.24/(31.2928)^2 = 0.15267

sin(theta)*cos(theta) = 0.15267 can be solve graphically. The first valid solution is 8.89 degrees.

So yes, a bus (with no friction) can cross a 50 feet gap, if the ramp was at an incline greater than 8.89 degrees.

Yay.

I like how people complain about that bus jump.

[DavidTC]

They actually did that bus jump. It's real. And, no, they didn't edit out any ramps.

They had to used CGI to edit the landing area shorter, to make it look like it landed closer to the edge than it actually did, because the bus actually jumped farther than it should have. (And they edited out the camera rig it smashed into.)

How? The gap is not level. Yes, it looks that way on film from certain angles if you're not paying attention, but the starting end was a several yards higher than the back end. Everyone sits there and complains about how a bus cannot do a level jump, and fails to notice that it's not a level jump.

About the only physics that stunt played fast and lose with was by weighing down the back somewhat so the bus wouldn't rotate forward, and, thus, still be movable after landing.

Re:I like how people complain about that bus jump.

[eldavojohn]

They had to used CGI to edit the landing area shorter, to make it look like it landed closer to the edge than it actually did, because the bus actually jumped farther than it should have. (And they edited out the camera rig it smashed into.) Um, there was no gap. The gap was edited in. In all sources I've found, they even talk about the ramp.

According to Wikipedia, you don't know what you're talking about:

Notes

One of the most famous scenes in the film shows the bus jumping across a gap in an elevated freeway-to-freeway ramp while still under construction. Both sides of the gap are at identical heights, making it impossible that the jump would work in real life. According to the "Making of..." feature that accompanied the DVD release, the stunt used a ramp and really did traverse fifty feet in the air. To handle the sudden jolt on landing, the stunt bus had no passengers aboard and the driver was wearing a shock-absorbing harness.

The gap in the highway was added through CGI; note the flock of digital seagulls added by the special effects company to enhance the realism of the scene. While the flyover ramp is shown to be essentially all complete and paved, except for the gap, in actual construction that gap in the road deck would have been fixed before the guardrail and asphalt is added. You may also note if you look closely, when the bus is flying over the bridge that is under construction the gap between the two bridges was edited in. And IMDB.com seems to agree:

The bus jump scene was done twice, as the bus landed too smoothly the first time. The bridge was actually there, but erased digitally. So you seem to have your facts wrong there. Please cite your source, I would find this interesting as I've always heard the above.

You should really write the authors of that paper though, I think they'd get a kick out of your comments and they'd love to add you as a data point.

Movie physics, game physics, and reality

[Animats]

I used to do animation tools for physically based animation, and got some idea of the Hollywood view of dynamics.

A basic concept in filmmaking is that the endpoint of a motion is predetermined. Directors think in terms of "here, then here, then there". The path desired is quite likely to be physically unrealistic, and may have to be pieced together from several shots.

A real physics simulator just isn't "directable" enough. What's used in practice is a combination of hand animation, piecing together motion capture, a collection of clever tricks to make real-world objects go where you want them, and lots of cuts to hide discontinuities. The MTV-style "one cut per second" approach to action scenes makes it even easier.

Much the same thing happens in games, except that you have to allow a user with limited control to drive a character with too many degrees of freedom and not enough embedded smarts to manage movement against real-world physics. This is why, in most sports games, you see beautiful motion-captured motion interspersed with strange jerks as motions are blended in ways that are continuous but nonphysical.

In most driving games, the physics is totally unrealistic. The wheel adhesion is huge, the CG is very low (often below the ground) and it's very common to lock roll rate once the vehicle is tilted beyond recovery angle, so that the vehicle rolls all the way over and lands upright. Driving a full sized car through a remote joystick works badly (we tried this with our DARPA Grand Challenge vehicle once, then immediately bought a MoMo steering wheel and interfaced it) and game controller joysticks are even worse. So the vehicle model has to be incredibly forgiving.

There is a classic of computational Hollywood physics worth noting. In the Bond movie, "The Man with the Golden Gun" (1974), a car is driven over a ruined arch bridge at high speed, executes a 360 degree roll, and lands on the far side. It really did do that. The dynamics were calculated by the Cornell Aeronautical Laboratory (now CALSPAN) and the ramp was constructed to make it happen consistently if the vehicle was driven at the correct speed. But there's a cheat there, too. The car had a fifth, solid wheel underneath which hit a rail on the launch ramp to initiate the roll. It wasn't possible to induce enough roll rate fast enough through the vehicle suspension.