Really, there are just three things I need to estimate: the length of the web during the swing, the speed of MJ at the bottom of the swing, and MJ’s mass. Finding the mass is the easiest. I can just look up the measurements of Zendaya Coleman, who plays MJ. I’ll go with a mass of 59 kilograms, an estimate on a celebrity biography page—this might not be accurate, but in the end, this value doesn’t matter too much.
For the length of the web (and thus the radius of the circular motion), I’m comparing their motion as they go past a building. Based on counting the number of rows of windows on the building, it seems like the web is at least 8 stories long. There is no standard height for a building story, but let’s just go with 4 meters per level, for a total web length of 32 meters.
The speed is a bit more difficult, but I’m going to do my best to get a reasonable value. If I know the distance that MJ and Spidey move (I will call this Δs) and the time it takes them to cover this distance (Δt), then I can calculate the average velocity.
The time isn’t too difficult. Looking at one of the swings, I can mark the frames showing the beginning and end of the motion. Since the trailer is recorded at 24 frames per second, I can get time data from the frames. Using this, I get a time of 0.417 seconds from the start of the swing to its lowest point.
Now, if I estimate the starting swing angle (θ), I can get the distance from the arc length (arc length = rθ). Let’s go with an initial angle of 30 degrees.
That’s everything I need. Here are my calculations, using a Python program. You can edit and change the values and run it again if you want to try different values.
Using my estimates, MJ and Spidey would be traveling at almost 90 miles per hour (40 meters/second), and MJ would have to support an equivalent weight of around 800 pounds (3,555 newtons).
It’s sometimes useful to talk about stuff like this in terms of g’s, where 1 g is equal to 9.8 m/s2. One g is what you feel if you are just sitting still, with no acceleration.