The Physics of the Speeder Chase in 'Solo: A Star Wars Story'

From Wired - March 12, 2018

I make it my job to hunt through all the best trailers and find some cool physics thing to explore. In this case, it's the trailer for Solo: A Star Wars Storythe Han Solo-led movie, scheduled to come out in May, that takes place some time before Episode IV: A New Hope. Right at the beginning, we see Han driving some type of speeder in a chase scene, taking a super-sharp turn with another speeder in pursuit. Here's the interesting physics stuff: Notice how it looks like it is sliding around the curve? Why does it do that? Is that how you would actually drive a make-believe speeder?

To answer these questions, we need to think about the nature of forces. Suppose I push on some object at rest such that my push is the only significant force on that object. This could happen with a boat sitting in still water, a hockey puck on ice, or a small spacecraft out in deep space (do not worry about how that object got into space). What does the object do? A common answer will be to say that the object moves. That's not wrong, but "move" is not the best answer. With a constant a force, an object increases in speedthat is to say, it accelerates. Acceleration is a measure of the change in velocity of an object, so we could also say that a force changes an object's velocity. That's key.

There's one more really important idea to understandvelocity is a vector. A vector is a quantity in which the direction matters (other vectors are: force, gravitational field, position). If a quantity does not depend on direction, we call that a scalar (like time or mass or electric charge). Since forces change velocity and velocity depends on direction, this means that it takes a force to change the direction of a velocity. Or you could say it takes a force to turn Han Solo's speeder.

How about a demonstration to show you how this works? Suppose I take a bowling ball and roll it along the floor (everyone should have a bowling ball handy for physics demos). This ball will essentially act like an object moving with a constant velocity since the frictional force is small. I want to make this ball change directions by hitting it with a stick. Which way should I hit it? Watch this.

Just to be clear, let me include this diagram showing the velocity of the ball and the direction of the force.

This sideways tap makes the ball change direction of its motion, but it does not really change how fast it rolls. So really, you can break forces into two components.Forces in the same direction (or opposite) direction as the velocity either make it speed up or slow down. Forces that are perpendicular to the motion (sideways forces) make the object change direction. But you already knew that: When you swing a ball around on a string, it mostly moves at a constant speed but the sideways force from the string causes it to change direction and move in a circle.


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