Life Made Easy

How to Spot Fake Video Stunts—With Science

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I hope you already know you should not imagine each crazy-awesome factor you see on the web; there’s lots of faux stuff on the market. However don’t fear, it’s doable to make use of physics and video evaluation to see what’s actual and what’s not.

On this case, some guys tweeted out this cool-looking soccer trick: One dude kicks a ball towards a wall that has an overview of a soccer objective on it, with two holes within the higher corners. On the similar time, one other man tosses a ball from the facet, and when the balls collide, they ricochet into the holes like billiard balls. It appears to be like magical. Alas, it is faux. Should you look carefully, you possibly can see a cloud make a bizarre transfer, indicating a video edit (as noticed in an observant tweet).

But it surely’s extra than simply glitchy clouds. This soccer trick additionally breaks some physics guidelines. Actually, that is the enjoyable half—utilizing some basic concepts to point out that the video is faux.

Unlawful Movement

I will begin with the ball that is tossed from the the facet. I can simply measure the movement of this one as a result of it’s transferring throughout the digicam’s visual view. Utilizing the Tracker video evaluation instrument, I can mark the horizontal and vertical location of the ball in every body of the video. Additionally, by trying on the body price, I can put a time stamp on these coordinates.

With that, I get the next plot of horizontal place vs. time for the tossed ball:

The important thing factor to see right here is that the information is linear. This implies the ball strikes within the horizontal path with a relentless velocity (which is the slope of the road). I get –6.844 m/s (about 15.three mph). Is that OK? Properly, should you throw a ball, there is just one power performing on it after it leaves your hand (assuming it is going sluggish sufficient to disregard air resistance), and that’s gravity. Because the gravitational power pulls solely within the downward path, it does not have an effect on horizontal velocity. With no horizontal forces, there is no change in horizontal movement. So this checks out.

What concerning the vertical movement? The downward-pulling gravitational power depends upon the mass of the item in addition to the native gravitational area (g = 9.eight newtons per kilogram). Because the vertical acceleration additionally depends upon the mass, free-falling objects will all transfer with the identical acceleration—it doesn’t matter what the mass. This vertical acceleration has a worth of –9.eight m/s2. Now, how do you measure the acceleration of a soccer ball from the video? If an object has a relentless acceleration, then its place ought to agree with the next kinematic equation:

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