As the smell of holiday food favorites wafts through the house and the littlest guests become restless, you can entertain and learn a bit about physics at the dinner table. Most of these experiments can be done with the tools at the table, but a couple take a little preparation.
The Two-Fork Balance
Use a little physics to wow the cousins and get two forks to balance on a toothpick off the rim of a glass. Find out how to do it and build upon the theory with additional challenges listed below.
Gather: Two forks that are the same size, a toothpick, and a glass.
Intertwine the tines of the forks so they are snug. You should be able to pick up one fork without the other falling off. This is going to be tricky for the youngest engineers, but worth getting right. Now, stick the toothpick about halfway between the two forks right through the tines. It is important to get this as close to the center as possible, but if it is not perfect, this will still work.
Carefully place the toothpick on the edge of the glass. You will need to move it back and forth a bit to find just the right spot before letting go. Once you find the sweet spot and let go, the two forks, which are relatively heavy compared to the toothpick, will balance off the edge of the glass.
For an extra challenge, and only with adult supervision, you can take a match or lighter to the toothpick and light it. Yes, light the toothpick. It will burn down, but only to the edge of the glass.
Science Moment: This demonstration is about finding an object’s center of mass. The object here is the two-fork contraption, but it could be anything. You could do it with a knife or a serving spoon, however finding the center of mass and sticking those on a toothpick is fairly tricky. The toothpick stuck in the tines simply adjusts the center of mass of the forks so you can balance outside them. With the littlest guests, try balancing a spoon on their finger. By moving the spoon around, they can find the spot that is the center of mass for a single utensil.
The Density Test
The density of liquids is fun to play with and very accessible even for young children. Most folks understand that oil floats on top of water, but what happens if you add other liquids? Do they float on the water or sink beneath?
Gather: A clear glass (or a clear glass jar with a lid for extra fun), a few drops of food coloring, and various liquids, such as cooking oil, water, honey, dish soap, corn syrup, or milk.
Add some water to your container and a few drops of food coloring. It will help everyone easily identify the water during the experiment. Slowly add the cooking oil. What happened? The oil is less dense than the water, so it floated on top. Now try milk. What happened? Make as many layers as you have liquids.
For an extra challenge, carefully drop in a button, cork, or a small plastic toy brick.
Science Moment: Different liquids have different density. Density is about mass and volume, or about how much of something is in a given amount of it. One way to think about density is the old joke about which weighs more: a pound of feathers or a pound of rocks? They both weigh the same, so they would have the same mass but the space the feathers take up is far greater. Feathers are less dense than rocks.
The Marshmallow Catapult
Before even thinking about this demonstration, get Grandma’s permission! Catapults are a super fun way to explore fulcrums and levers — and to fling things at each other.
Gather: Plastic spoons, craft sticks, rubber bands, corks, and mini-marshmallows
Rubber-band your spoon to a craft stick. Attach it under the bowl of the spoon. Next, attach a second craft stick to the bottom of the first stick near the handle end of the spoon. Now you have a spoon attached to one craft stick and that stick attached to another stick. Carefully slide the cork between the two sticks, so from the side you see the round ends of the cork. Now you have a catapult.
Starting at one end of the table, see how far you can launch a marshmallow. Put the marshmallow in the bowl of the spoon and gently pull the bowl back with your finger. Let go and the marshmallow will launch. How can you adjust the catapult to help the marshmallow go farther? [Hint: the cork has a sweet spot that will help the projectile achieve maximum distance.] Can you improve your accuracy and try to get the marshmallow into a cup?
Science Moment: Catapults are very simple machines that demonstrate a huge amount of physics, math, and history. First, the easy part: The stick with the spoon is a lever and the cork is a fulcrum. These are two of the six simple machines that also include the wheel/axle, incline plane, wedge, pulley, and screw. Another example of the lever-and-fulcrum team is a teeter totter. Now for the harder part: potential and kinetic energy. The lever has loads of potential energy when it is pulled back, which will turn into kinetic energy at the point of release.
Bonus Food Science Ideas
Put cranberries in water or see if cranberries bounce. Another cool thing to try with cranberries is to toss a dried cranberry and a fresh cranberry into a carbonated beverage. What happens to them?
Science is best served to kids with a curious adult on the side. Kids always respond to an adult who is excited and willing to take the journey with them.