The Energy of Toys
This video explores the chemistry behind simple toys that showcase energy changes. It can be used as a supplement to an investigation, or may stand on its own to introduce a lesson or extend student learning.
What, exactly, is energy? Because we can’t see it, coming up with a formal definition for energy can be tough. However, we can see how energy is transferred from one form to another. For example, put a battery in a flashlight and soon we get light out the other end.
Energy is the ability to do work and make things change.
Best of all, we can understand energy by playing with some classic toys.
Meet my friend Trevor, the amazing drinking bird. The amazing drinking bird is a toy that has been around for over 50 years. It looks like a bird, and will bob up and down as it appears to drink out of a cup of water placed in front of it.
But how does it work?
Well, the amazing drinking bird is made out of glass and contains a red liquid. The head and tail are bulbs connected by a narrow glass tube. The only way for liquid to move between the head and the tail is through this narrow tube. A felt-like fuzzy material covers the head and beak.
The red liquid inside the bird is actually methylene chloride, also known as CH2Cl2. Methylene chloride is a very volatile liquid, which means it evaporates easily—easier than water. Most of the air has been removed from the inside of the bird before the liquid is added, making it even easier for the liquid to vaporize.
Wetting the head of the bird starts the action. After wetting the head, the red liquid inside the bird slowly begins to rise from the bottom bulb up to the head. This changes the center of gravity and the bird begins to tip down into the cup of water. As the bird tips over, the liquid then flows back into the bottom bulb, lowering the center of gravity and the bird stands upright. Then the process repeats.
So, where’s the chemistry here?
Well, when the bird’s beak gets wet, it causes the inside of the head bulb to cool. As the inside of the head cools, the methylene chloride in the head changes from a gas to a liquid, lowering the vapor pressure inside the head. Because the vapor pressure in the tail bulb is now greater than the vapor pressure in the head bulb, the liquid is pushed up into the head bulb.
Another neat toy that can teach us about energy is called a jumping disc.
The disc is about an inch in diameter and made of thin layers of two different types of metals. It is slightly concave. To make it jump, the disc is taken in the hand and rubbed between the thumb and fingers. This warms the disc and makes it click into a convex shape.
When the disc is then placed on the table, it is still for a moment, then it jumps into the air a foot or more.
So where does the energy come from to make the disc jump?
These discs are made from two different types of metal, sandwiched together into a very thin layer. One of the layer tends to expand when its temperature increases while the other layer does not. As the disc is warmed, the temperature sensitive strip of metal grows slightly larger which causes the disc to snap from a concave shape to a convex shape.
When the disc is placed on the slightly cooler countertop, this same layer begins to contract, and the disc snaps back into its original shape. The force of this transformation launches the disc into the air.
So how is energy involved in this toy?
Thermal energy is transferred from your warm hand to the cooler disc. This warms the metal strips in the disc itself. As the temperature increases, the atoms in the metal move faster and spread further apart. The inert layer resists change, due to the way its atoms are arranged.
So, when the warm disc changes its shape, it has a higher potential energy. When it snaps back to its original shape, this potential energy is converted into kinetic energy and the disc jumps.
Although we’re more likely to focus on the batteries in our smart phones, these simple toys are a fun reminder that energy is all around us.
Isn’t that right, Trevor?
Download Video Transcript