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Make a Spitting Monster Toy
In this science experiment, kids explore gravity and air pressure while making a spitting monster toy that is perfect for Halloween!
The forces of gravity and air pressure act on the water inside the bottle. Gravity is a force that pulls everything down toward the earth. It is pulling downward on the water inside the bottle (and the bottle itself) -- but gravity's pull on the water is the same whether or not the cap is on the bottle, so this not what is controlling the "spitting." It's changes in air pressure make the water squirt out: when the cap is loosened, air can get inside the bottle, and the air pressure begins to force the water down and out. When the cap is tightened, the air pressure stabilizes (meaning, it becomes the same both inside and outside of the bottle) and so it stops pushing the water out of the bottle.
Safety Notes
Only an adult should make the hole in the water bottle. As always, be careful when using force with a sharp object.
Materials
- Plastic water bottle with lid - green preferred - 1 of this item per student
- Craft materials
- Water
- Sharp object to make a small hole
- Sink, bucket or similar
Instructions
Be sure the bottle is at room temperature. If it is cold, it will "sweat" and you won't be able to decorate. Peel off any labels. (Note: if you are doing this with a water bottle that has never been opened, there is no need to empty the bottle first; just be sure to leave the lid on. This is a great way to do this activity with a large group of kids, as you can skip the later step of filling the bottles with water.)
ADULT SUPERVISION: Poke a small hole in the bottle about 2" up from the bottom using an awl, sharp knife tip or similar. This will be the "mouth." (Note that when we made the model in the video, the knife made an uneven hole, which made it look like water is spitting out of two sides of the mouth. Also note that it is OK to do this with a bottle that is already full of water, provided the cap is on tightly. Water should only come out when you squeeze the bottle.)
Holding your thumb over the hole, fill the bottle with water and screw on the cap tightly. Once the cap is on, no water should come out of the hole on the side unless you squeeze the bottle.
Now decorate the bottle to look like a monster. Be sure to put the "mouth" around the hole in the side.
To experiment, hold the bottle over something to contain the pouring water and slowly unscrew the cap. Water will “magically” spit out of the mouth. Now screw the cap back on -- the bottle stops spitting! Repeat until the water is gone; refill as many times as you'd like. (Note that any pressure on the sides of the bottle will make a little water come out, so to create the illusion of a magically spitting bottle, be careful not to squeeze the sides.)
