# Incorrect physics in movie

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1. Jan 27, 2017

### jessle

1. The problem statement, all variables and given/known data
I have a project that involves explaining the incorrect physics that happens in a particular scene of a movie. I chose to do Furious 7 and the scene where dom rolls out of the car because the brakes stopped working and the car crashes falls out of the tower. I need at least 3 points of what's wrong with the physics and what should have happened in reality. any calculations or diagrams would be helpful too. here is a clip of the scene and skip to 2:50 for what i'm talking about... Is there anything I can calculate to prove how the physics is wrong? any help is appreciated. thanks

2. Relevant equations
p = mv? - to calculate the car's momentum?

3. The attempt at a solution
So far, I know that Dom should have fallen out of the tower with the car since he was travelling the same speed as the car (correct me if I'm wrong). he didn't grab onto anything to stop himself from falling off the ledge he just stops rolling right at the edge. When the car crashes into the ground, it is close to the building, is that supposed to happen?

2. Jan 27, 2017

### phinds

It looked to me like he COULD have slowed his roll so I don't think that's totally impossible. People are not like a hard object, they flop around. The car landing right next to the building is, as you noted, impossible

3. Jan 27, 2017

### Student100

This is in Dubai right? You might start with google mapping the buildings if they exist and figuring out the distances between them. Then look at what speeds the car would need to achive to make the jump across them. You could also look at forces the drivers would experince upon landing, and the potential damage to the vehicle that might cause. Also figure out how big the floors are for these towers. Are they 30 meters across or 300. That matters.

You should probabaly also look up the specs on the vehicle, turn radius, accleration, etc. That will also help seperate what is plasuable and what is fiction.

Him stopping before flying out is also not entirely fiction, from just watching. The cars distance after falling out is also not something i would so quickly throw into the fiction bag.

You should start gathering data and let that guide you, rather than just gut instinct.

4. Jan 28, 2017

### Cutter Ketch

The scene in the second building seems too long. Estimate the speed of the car from an exterior shot (e.g. time to travel its own length and v = d/t) then multiply by the length of the scene to get the displacement. How big would the building have to be?

In the jumps between buildings the car didn't fall far enough an didn't have enough vertical speed when it reaches the other building. Determine the distance between buildings using Google Earth. It actually has a feature for measuring distances by clicking. Estimate how far the car fell from an exterior shot. (Typically 5m per floor) then determine how fast the car would have to be traveling by a simple trajectory calculation. (Y = 1/2 g t^2, X = v t, so t = X/v. Substitute and Y = 1/2 g X^2 / v^2. Solve for v to get v = sqrt(g X^2 / (2 Y^2)). I'm sure it will come out ludicrous.

When he was cutting donuts in the third building and the speed was nearly 0, why not let off the gas, or take it out of gear? At that point the momentum is practically zero. The car won't accelerate unless he accelerates it. Why is he still standing on the gas? It's the brakes that are broken not the accelerator.

Similarly, why did the car accelerate and go flying out the window? If you don't step on the gas pedal the car accelerates very slowly at best. Being a manual transmission, you can step on the clutch (ok, probably not in this super car) or put it in neutral and it won't accelerate at all.

5. Jan 28, 2017

### DaveC426913

I think the least plausible thing in the whole clip is the jump from tower to tower.
The moment the car leaves the first building it is in ballistic flight, and begins falling at 10m/s2. No amount of speed imparted by the car will stop or even slow that rate.

The best it can do is have enough speed to cross so fast that its touchdown has a much higher horizontal component than vertical component.

What angle can such a car plausibly land and still remain mostly a car? 30 degrees? That means its forward motion would have to be about twice its falling speed.
Its falling speed can be calculated by knowing the distnce between towers.

6. Jan 28, 2017

### Student100

I actually offhand thought the least plausible scene was the turning inside the building, the jumps seem plausible assuming the buildings are less than 200ft and hes going 110/120mph at the time of flight.

The angles of reentry seem off, but we need the OP to furnish some data if the buildings are real/specs for car exist.

7. Jan 28, 2017

### DaveC426913

I'd say that's an overestimation. Most floors are typically ten feet or so, which is between 3m and 4m.

Sears Tower in Chicago is 108 floors, its highest floor being at 412m - meaning each floor on averge is 3.8m.
One World Trade Center is 104 floors up to 368m - or 3.5m per floor.

8. Jan 28, 2017

### DaveC426913

If that were his speed, he'd cross 176 feet of floor in one second. (Assuming a constant speed.)

Have to check that car's acceleration. How fast (how short a distance) can it get to 120mph?

I'm not sure he could make more than 1 maybe 2 gear changes in that time.

9. Jan 28, 2017

### Student100

Yeah good question. I dont even know what that car is.

10. Jan 28, 2017

### DaveC426913

11. Jan 28, 2017

### Student100

12. Jan 28, 2017

### DaveC426913

13. Jan 28, 2017

### Student100

Yeah, but we have to remeber that he was doing circles before punching it. Let me see if i can find those skyscrapers so we can determine distances and how large the floor plan is.

14. Jan 28, 2017

### Student100

Were not the first to try to work this out apparently:

http://www.vulture.com/2015/04/could-furious-7s-skyscraper-jump-really-happen.html

Buildings are real, this has the names and some approximate distances. The city is Abu Dhabi ( I was close!)

Not sure if we're maybe doing to much for OP in hw section though.

15. Jan 28, 2017

### DaveC426913

16. Jan 28, 2017

### CWatters

When the car hits the ground it suddenly starts spinning/rolling rapidly. It's not clear what causes that. Conservation of angular momentum fail?