Ski Incident Physics. An Analysis of an Expert’s Physics Analysis.

Rhett Allain
6 min readMar 31
Photo: Rhett Allain. This is me in the court of physics (but actually it’s at NASA Stennis Space Center)

I’m not really a big fan of legal trials — it’s not something I’m going to follow all of the details. This is especially true for something like the case of Sanderson vs. Paltrow. The case is basically a civil suit over injuries sustained between this one guy and Gwyneth Paltrow. I suspect that no one would be paying attention to these court proceedings if it didn’t have a celebrity involved. But whatever.

Oh, and now look — I’m interested. Why? Because there’s some physics. You know I’m a big fan of physics. I’m sort of like physics paparazzi — I follow it around and look for some cool stuff to take photos (or calculations). Maybe that makes me more like an ambulance chaser for physics. Who knows.

Here’s the very basics of the case. There was a collision the ski slope between Paltrow and Sanderson. In the process of the impact, Paltrow and Sanderson feel onto the ground with Paltrow landing on top. It seems both parties agree on this fact. Sanderson was injured (broken ribs) and that’s where we get into the physics.

Calculating Impact Force

I want to focus on the video that keeps popping up. This is Dr. Irving Scher — the expert witness for the defense. He has a PhD in mechanical engineering and studies all sorts of things related to skiing. Here’s a shorter version of his testimony.

In the first part of his presentation (or whatever you call it), he explains how an expert witness (Dr. Richard Boehne) for the plaintiff is incorrect. Boehne estimated the impact with the ground produced a force of 4680 Newtons. His basic calculation goes like this:

Image: Court TV

Let’s go over this stuff. First, he is assuming that the human body is a single point mass located at the center of mass (which would be right above the waist for a normal human in a normal…

Rhett Allain

Physics faculty, science blogger of all things geek. Technical Consultant for CBS MacGyver and MythBusters. WIRED blogger.