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Don’t ask why—you need to escape, stat. So how do you make a break without breaking every bone? We asked Rhett Allain, an associate professor of physics of Southeastern Louisiana University, to walk us through the best way to jump from a moving train (while limiting risk of injury, of course).

Turns out you have some options.

Strategy #1: Decrease Your Starting Velocity

If you simply jump from a train moving at 10 meters per second (m/s), you’ll hit the ground. During impact, you’ll have a vertical velocity, because the train is higher than the ground. As you move down, the gravitational force will increase your vertical speed, as if you jumped off a stationary train. If the train is 1 meter high, you’ll travel down at 4 m/s.

But you’re also moving horizontally along with the train. So jumping would mean that upon impact, you’d move 4 m/s down and 10 m/s across. And it’s not the speed that causes injury—it’s the acceleration, or the change in velocity divided by the change in time.

Just as speed tells you how fast your position changes, acceleration describes how your speed changes in meters per second per second (m/s2). There isn’t just one “safe” level of acceleration, but an acceleration of 10 m/s2 is safer than 40 m/s2.

To decrease your acceleration on impact, decrease your starting velocity. If the train is traveling at 10 m/s north, you need to run 4 m/s south inside the train before jumping. Velocity is relative, so this puts your speed with respect to the ground at only 6 m/s north.

Option #2: Increase Your Starting Time

Ideally, you’d use a sled to jump out of the train, so you could slide along the ground after jumping. But your next best bet is landing with a barrel roll. The key is to increase your stopping time to decrease your acceleration.

No time for doctors when you’re on the run.

This article appeared in the October 2019 issue of Popular Mechanics. You can subscribe here.

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