Hey Ray! Understanding Static Equilibrium
PITTSBURGH (KDKA) -- Sometimes, seemingly real things on the internet turn out to be fake, and sometimes seemingly fake things on the internet turn out to be true.
We recreated a "trick" you may have seen online where a bottle is hanging from a string, and the only thing holding it up is a toothpick.
This probably looks very odd to you, considering the toothpick is much lighter than the bottle, and you don't see anything holding the toothpick to the table. When I saw this online, many of the comments said they believed it was fake.
This is one of those things that look fake but is real. This is actually a really cool demonstration in physics. Let's break it down.
If the bottle were just hanging from a string and the toothpick on the table, the results would be as expected. The bottle, the string and the toothpick would fall. However, the magic....or physics, happens when you add in two more toothpicks. While it does not look like much, these two additional toothpicks are what make this whole thing stay put.
Remember when we mentioned "upward force" before? It is a subtle thing mentioned in several of our experiments. If something is being held up by something else, there is an upward force. Here, we have the table providing an upward force to the toothpick. The bottle hanging from the string is providing a downward force. Normally, that would pull the toothpick off the table. However, when you add in the other two toothpicks, we are creating a system that basically cancels out the forces.
It is called "static equilibrium". Static equilibrium is a physical state in which all the components of a system are at rest and net force is equal zero throughout that system. Sort of like 2 people who weigh the same on a teeter totter.
In this physics demonstration, the table has an upward force to hold the toothpick.
There is a downward tension on the string.
The toothpick between the two strings creates torque, or a twisting force that tends to cause rotation.
That rotation pushes up on the third toothpick, which returns that to the original toothpick, cancelling everything out, or leaving us with a net force of zero and the toothpicks at rest.
If you try to recreate this yourself, I learned safety glasses should be worn. The forces that this experiment can provide can cause the toothpicks to pop outward. Learn from my mistake, and wear eye protection! It is a good thing there were no injuries while performing this experiment!
To set this up, you need 3 toothpicks, and bottle of water and some string or thin rope. It is best to hang a toothpick over a tables edge. Make sure the table has a sharp edge and is not rounded. Place something with weight on the toothpick. If it is heavier than the water bottle, it will work. We used a brick, and the original post used a gallon of milk.
Hang the water bottle from the string and hang that string on the toothpick.
Now, place a horizontal toothpick between the two sides of the string, finally place a third toothpick that goes from the horizonal toothpick to the original toothpick (this can be difficult).
Lift the brick and see the physics in action!
