Inertia Ring

Inertia can be a bit confusing until you see it revealed by a falling hex nut

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The object of this activity is to get the hex nut to drop into the plastic bottle. Simple enough but there will be something in the way. To accomplish the drop, you’ll need a combination of careful setup, Isaac Newton’s smarts, inertia, and gravity. Balance a plastic ring on the mouth of an empty soda bottle and place the hex nut (or similar heavy, small object) on top of the ring.  Correctly remove the ring and the hex nut drops straight into the bottle.

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Here's What You'll Need

  • Hex nut (more is even better)
  • Plastic ring
  • Empty soda bottle
  • Adult supervision

Let's Try It

  1. Vertically balance the ring on the mouth of the empty bottle. The ring needs to be as round as possible and not mooshed on one side.

  2. Set a single hex nut vertically on the ring at the highest point on the ring. Make sure the hex nut is directly centered over the opening of the bottle.

  3. There’s a way to smack the ring so the nut drops straight down through the mouth of the bottle and falls to the bottom.

    Consider some possibilities and then test them. Hit the ring so it moves to the side and allows the nut to drop straight down. HINT: Remember that plastic flexes when you hit it.

    When you have a technique that works, pile on the hex nuts and go for a world record!

How Does It Work

One of the three Laws of Motion that Sir Isaac Newton identified (the First Law in this case) states an object at rest will remain at rest unless something smacks it and makes it move (OK, maybe those aren’t his exact words). By hitting the ring on its outside, you overcome its stationary inertia, it moves all right, but the plastic flexes upward at the same time. That upward flex overcomes the hex nut’s stationary inertia and pushes it up and away from the bottle until gravity curves it back down to the table. No “plunk” sound with that one.

However, when you hit the ring on its inside, the plastic flexes downward. The plastic actually drops out from under the hex nut and zips off sideways. Obviously the hex nut has lost its support but, because it’s not moving due its stationary inertia, it doesn’t do anything… for a few nanoseconds that is. Gravity overcomes the hex nut’s stationary inertia and moves the nut straight down into the bottle.  It may take a little practice to get the nut to drop into the bottle but once you get it, you’ll love the sound it makes!

By the way, once it’s moving, the hex nut won’t stop moving, speed up, slow down, or change directions either (due to its moving inertia) unless something (like the bottle, your hand, the floor, or the ground) gets in the way and causes any of those options to occur.

Take It Further

You can guess that increasing the number of hex nuts doesn’t change the outcome as long as they’re stacked carefully. Stack them so they lay on their sides horizontally. They all need to fall in as a stack so keep them lined up.

Stack the hex nuts vertically instead of horizontally. This gets tricky the more hex nuts you use. You’ll want to do this on a day you don’t have caffeine.

You can use other objects for this activity like a stack of pennies, a new, unsharpened pencil, or a marker with a flat end on it. What else can show inertia using this drop method?

Using a phone feature or a video camera, take slow motion videos of your tests. Capturing your tests in slow motion will reveal some very interesting details you just can’t detect with your eyes.

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