The Physics of Leia Using the Force
Now that Star Wars: The Last Jedi is out on DVD (and digitally), I think it’s safe to discuss one very interesting scene in the spirit of May the Fourth. However, there is a chance you haven’t seen it—so this is your spoiler alert.
In this scene, Leia’s ship is attacked by the First Order. The attack knocks a hole in the bridge, which causes the air inside to push out most of the crew in that area—including Leia. So there she is … just floating away from the spaceship. But wait! Leia is still alive. She reaches out her hand and uses the Force to pull herself back to the ship.
Some people thought this whole scene was silly, but I don’t think so. It shows that Leia is indeed like her father and brother in that she too can use the Force. It’s really the only time we have seen her do something like that. OK, I guess that time she heard Luke calling her on Cloud City was a use of the Force—but still, this was important.
Other than showing Leia’s powers, this is also makes a great physics question: How much force did the Force apply to Leia to get her back to the ship? Let’s do this.
I suppose we should start from some fundamental ideas. In particular, the nature of force and motion (not the Force, but the physics force). A force is an interaction between objects that causes a change in velocity. Change is the key word here. Forces do not make things “move,” forces make things change the way they move. One way to express this idea is with Newton’s Second Law. As an equation, it looks like this:
The little arrow symbols over the variables just mean they are vectors. Don’t freak out, please. If you want, you can ignore the arrows since Leia will just be moving in one dimension. But from this equation you can see that we can calculate the force of the Force if we know both the mass and acceleration of Leia. The acceleration is a measure of how fast the velocity changes—but you can see that we are getting into some kinematics (the physics dealing with motion).
Let’s set up some parameters of this motion. It might go something like this:
- Explosion. Boom. Leia leaves the spaceship with some initial velocity (from the air pushing her out).
- She keeps moving away from the spaceship at some constant speed for some time interval (to be determined). Oh, in space there would be no forces to slow her down so she would just keep moving away.
- Leia makes a decision to not die and remembers that she can use the Force. This Force exerts a force on her to slow her down and then speed her back up towards the ship (here is where I calculate the acceleration and the force).
- I’m not sure if she keeps accelerating all the way back to safety or just coasts in. Based on the video, she doesn’t seem to be moving that fast at the end. I’m going to say she coasts.
But for a lowest order approximation, I need to estimate two things (and then measure one from the video). I need Leia’s starting velocity (before using the Force), her final velocity (after using the Force), and the time this takes. How about a starting velocity of -3 m/s (away from the ship), +4 m/s (towards the ship) and an acceleration time of 10 seconds (from the scene).
Now I can use the definition of acceleration (in one dimension) as:
With my estimations from above, this gives an acceleration of 0.7 m/s2 and a force (of the Force) at 31.5 Newtons—assuming a Leia mass of 45 kg. Boom. That’s your answer. But wait! You can make your own estimates and calculate this force. I made it easy for you with this simple calculation in python (python should be your calculator).
Yes, that’s not a very significant force—only 7 pounds (if you prefer to use Imperial Units instead of Rebel Alliance Units). Go ahead and get your own estimates for the velocities and times and then edit the code above (trust me, you won’t break anything). Just click that “play” button to run the calculations.
Of course I can do more—I can also plot the motion of Leia’s entire trip out into space and back. Here’s what that looks like.
Also, here is the code (just in case).
You might still be wondering about one final question—could Leia even survive in space? I’m going to leave that up to you since it’s probably more of a biology question.