Gather your supplies, including an empty container and plastic bottles.

Supplies List

This is one of the least material-intensive experiments you'll find. Find two same-sized bottles, water, and a container to pour the water into (you could even use the bathtub, or your yard in the summer). Anything additional that you want to add is up to you and your kids. Try using food coloring, Monopoly houses or Legos, or duct tape if you want to see how the water goes from one bottle to another. You may also want to have a stopwatch to time how long the water takes to get out of the bottle.

Step 1

Fill both bottles to an equal amount of water. We found it worked best at about 60% full, but you could do more or less depending on how long you want the experiment to last. If using food coloring or other props, such as Legos, add them now, too.

Step 2

See how long it takes to pour the water out of the bottle just by tipping it upright into the empty container. You can use a stopwatch to record the time, or if two (or more kids) are participating, let them race by pouring both bottles at once.

Step 3

Turn the second bottle upside down and swirl it a little to create a vortex. A vortex is created when a fluid (air or water) travels in a spiral around a centerline. When you time the emptying of the second bottle, or race it with the first bottle, testers will find that the water from the second bottle comes out faster. This is because this water vortex makes it easier for air to come continuously into the bottle through the empty space in its center. Without the vortex, the air has to take turns coming through the bottle's opening, creating the glug-glug sound and feel.

Another Variation 

Another option is to try filling one bottle 2/3 to 3/4 full. Next, use duct tape to attach it to the second bottle, so the two bottle mouths are now attached. You can create the same mini tornado, or water vortex and pour it into the second bottle without having to refill the bottle to try the experiment again. 

If your kids like this experiment, consider purchasing a Tornado Tube, which is a little more effective than the duct tape. Or buy some colored lamp oil to put into the bottle with the water. Oil and water don't mix, so the oil will highlight the vortex, making it more visible than the rest of the water.

Photos by the author