Bone-Crunching Forces

Part 2: The Zipline Fall

Sometimes it can be fun to hang from your arms and swing around. However, as anyone who has jumped from monkey bar to monkey bar can tell you, there is significantly more strain and force when decelerating instead of hitting the ground.

Now lets take that example and extremify it!

Here we have, from 30 meters and 60 meters, an example of what not to do if you're trying to keep your arms attached to your body.

Lets find the velocity this player would have just before hitting the ground.

v² = 2*g*Δy => v = sqrt(2*g*Δy)

For Δy = -30m then v = 26.37m/s, and for Δy = -30m then v = 37.29m/s.


Another relation, F = m*Δv/Δt, gives the amount of force needed to stop our player.

For Δy = -30m, v = 26.37m/s, Δt = 0.233s, and assuming we come to rest:

F = m*Δv/Δt = M*([26.37 - 0]m/s)/0.233s = 113.18*M m/s²

For Δy = -60m, v = 37.29m/s, Δt = 0.167s, and assuming we come to rest:

F = m*Δv/Δt = M*([37.29 - 0]m/s)/0.167s = 223.29*M m/s²

Assuming, for the sake of chaos, that our player is a nice 75kg.

The force on their SINGULAR ARM would be 8,488.5N for the 30 meter drop, and 16746.75N for the 60 meter drop.


According to researchgate.net, the force required for dislocating and anterior shoulder dislocation is 203 Newtons.

The forces above are way over 40x and 80x the force required just for dislocation.

While I can't find any sources for exact numbers, the force required to pull apart a person's arm is about 2 times the force of a horse (from the good ol' dismemberment).

Either way, these forces are so high that if any human were to attempt to pull this stunt, they would not only lose their arm but would probably break the rest of their bones.