A common question I get asked after I perform is how I am able to do what I do. What’s the secret? How am I able to juggle five balls without the arches colliding? How am I able to run up a wall after bouncing on a trampoline? Questions like that. “Practice and no social life,” is usually my answer. But there is a lot more behind many of my antics and circus acts in general that when given enough thought, make the tricks easy to breakdown. The real secret behind so many circus acts: Science.
Next to performing, science is my biggest passion. I read about theoretical particle physics, have conducted research in the chemistry of food science, and tutor science in my school. I also find great joy in explaining circus using the physical laws that dictate why things work, and have given multiple presentations on this very topic. Science is everywhere; a flying trapeze is a pendulum, a human cannonball is a projectile, sway poles operate under the laws of center of mass, and a motorcycle globe is an example of centripetal force, to name a few examples. However, one of my favorite examples of circus science, mostly because it is easy and can be done by almost anyone, is the ol’ pulling a tablecloth out from underneath some dishes trick. The traditional presentation is a table is set with a few plates and glasses of water on top of a tablecloth, the tablecloth is pulled out, and everything is still on the table. Let’s see how it works…
Sir Isaac Newton’s first law of motion states that an object at rest (not moving) will remain at rest until acted upon by an outside force, and an object in motion will remain in motion unless acted upon by an outside force (force is equal to an object’s mass multiplied by its acceleration, Newton’s second law, for all you physics fans). Galileo Galilei stated that objects possess inertia. Inertia is what is responsible for an object’s ability to resist a change in motion. Inertia cannot be measured, it is just relative. The more mass an object has, the more inertia it has. An elephant has more inertia than an ant. In other words, it is harder to change the motion of an elephant than an ant. Get it? Good-let’s move on.
The items placed on the tablecloth, the plates and glasses, have a large inertia so that are less likely to be subject to a change in motion (rest). The performer quickly pulls the tablecloth out and for a small split second there is a force acting on the objects. However, they have enough inertia to resist large movements due to a the force of the tablecloth. The objects move a small amount, but still remain on the table.
Now hopefully you’re not confused, because it’s about to get worse. I mentioned that there is a small force acting on the objects from the tablecloth for a small split second, causing them to move slightly but still stay on the table. We are able to control the strength of this force with the type of tablecloth we use. The force acting on the objects is friction. What’s friction? Friction is the force responsible for surface resistance in regards to motion. Certain times friction is good. For example, you want there to be friction between the tires of a car and the road so the car doesn’t skid. In our case though, friction is bad. We want to make sure that there is as little friction as possible not only between the tablecloth and the objects, but also between the tablecloth and the table itself. In order to reduce this friction, this trick is best performed with cloths made out of thin, smooth fabric (I actually use a bed sheet…Shh! Showbiz secret!). The smoother the tablecloth, the weaker the force of friction and the less likely the objects on the table are to move.
While understanding how a trick works, it is nothing like actually going and doing the trick for yourself. So go get your smoothest fabric, a table, and your most valuable and expensive China (just kidding folks) and get going! Until next time, SCIENCE!
Want to know the science behind YOUR favorite circus trick? Email firstname.lastname@example.org and it may be explained here for everyone to see!