How the Physics of Cause and Effect Tell a Story, as Illustrated by Buster Keaton

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The application of Cause and Effect on stage is most obvious in slapstick physical comedy – trip, fall. But it extends far beyond that. Cause and effect relationships communicate because they are based on a common experience of the physical world. Everyone has been on a playground swing. Everyone has thrown or kicked some sort of ball. Whether or not it went where they intended is another matter, but even if it didn’t they experienced the effect as the ball soared along the trajectory they initiated, and then again as it shattered a window. And they undoubtedly flinched in response, which you might not think of as having a physical connection but what are they responding to exactly? The sight and sound of the window shattering – carried to their eyes and ears by light and sound waves. I know what you’re thinking. Wait, you mean I get to do theatre AND science?

Sort of. All you need is your innate “feel” for movements you experience daily because of Newtonian physics . And since physics is the same in Bangladesh, New York, or Antarctica, every audience on the face of this planet shares that innate sense with you. Furthermore, in the theatre, we can use this not only to connect actions with objects, but characters, emotions and even our audience.

Newton’s First Law of Motion

Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.

(You may have also heard an object at rest tends to remain at rest until acted upon by an external force. Same thing, just depends where you’re standing in relation to the object and the force. But now we’re getting into Einstein’s relativity and that’s another blog post entirely.)

Let’s see what Buster Keaton can teach us about this. First, the purely physical.


Self explanatory, really. Let’s take it a step further.

Boy meets girl
Here we see the same principle used to communicate a character’s interest. The movement is exactly the same as the first example, except instead of a car the external force is a girl, and even without physical contact you see the connection. No words or emoting necessary.

Of course sometimes a cause will affect an object or person’s momentum gradually rather than abruptly, so sometimes it looks more like this.WomanStops


Newton’s Second Law of Motion

The relationship between an object’s mass, its acceleration, and the applied force is Force = Mass x Acceleration

(Note: Mass is not the same thing as weight, but unless you are pretending to be in a different gravity field from Earth you don’t need to worry about that. For our purposes here mass is weight.)

This one is important. It means that if we indicate to the audience any two of these three things they automatically have an expectation about the third. And whether we fulfill that expectation or break it, we need to respect it. Because if you create an expectation and then unintentionally break or ignore it, you will lose your audience. Break it intentionally and you’re a comic genius. Again, let’s turn to Buster.

Fulfilling the expectation:


Breaking the expectation:

Falling house


If you show an object as having a certain weight and then throw it into the air with a certain amount of force, the audience has a feel for how high it will go and when it will come back down. By the same token, if you are a well-grounded character or in an emotionally heavy state it makes sense that affecting you requires a lot more force.

If you’re in a lighter or off-balance place, or just a generally lightweight character, a gentle “boo!” could make you jump all the way across the stage.

I love how this little moment from Steamboat Bill Jr. communicates so much – we know instantly that no one on either side of this argument respects Jr. in the least, and that Jr. himself lacks self-esteem. Despite his fancy clothes, he is (for the moment) completely powerless, not only physically but also socially and personally. Given his instant acceleration with relatively easy pushes, we surmise that he is a total lightweight.

Newton’s Third Law of Motion

For every action there is an equal and opposite reactionTheLook

The important thing to note here is that “equal” means that there is no loss of energy. The energy has to go somewhere. It does not mean that the cause and effect are the same motion. The exact effect that a transfer of energy causes is dependent on a number of things. We already saw in rule two how the mass (weight) of the effected person or object influences the outcome.

The direction of the effect may in turn be changed by another force – such as more cops.

Or by seeking a socially acceptable outlet.

The force might be applied indirectly.

Railroad Tie
The thing affected might not be solid.

Or stable.

It might be attached at one end.

They might be attached at one end.

Sometimes a force is elastic.

Sometimes it is countered and the effect is mutual.

The possibilities are endless. The point is, your audience understands cause and effect without having to think about it. Without  language. It is visceral. And that makes it a powerful tool for connection. In case you don’t believe me and Buster, check out Harpo Marx and Lucille Ball.


If you would like to learn more about Cause and Effect in practice, I am teaching a workshop on Saturday, April 30th. 2 whole hours of this stuff!

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