Air Pressure in a medicine syringe (or a turkey baster)

Use a turkey baster or, even better, a medicine syringe (not the kind with a needle, but like this Oral Medication Syringe , and play around with it.
Pull water up, push it out. What do you have to do first before you can get any water into the syringe? If you pull the syringe up half way before you try to draw in water, can you fill it up? How far can you fill it.
Why do you need to press it all the way down in order to fill it up with liquid? What’s happening when you press the syringe (or squeeze the bulb) all the way?
What makes the liquid fill up the syringe?

Another way to think about air pressure: It really is a good deal like the way mud comes up between your toes when you are barefoot. Your foot is pressing on the mud all around except in the spaces between your toes, and so the mud is forced up into these spaces. The air pressure on the water is like your foot on the mud, and the space in the medicine syringe is like the space between your toes. Since wherever there is air it is pressing hard, the only space into which it can force water or anything else is into a place from which all the air has been removed, like the inside of medicine syringe (or turkey baster).

If you have both a turkey baster (a giant bulb syringe) and a medicine syringe, use them both. What’s different about the way they work?

With the medicine dropper, why doesn’t the water just fall back out when you are not pulling on the plunger?

Is there a difference between the medicine dropper and the bulb syringe that makes the water stay inside of one better than the other?

The medicine syringe has a better seal, so no air is getting in the top at all. Also, with the medicine syringe, the hole in the bottom is too small to let the air squeeze up past the water, and therefore no air can take the place of the water that might otherwise run out. The seal of most turkey basters is just loose enough to allow air to seem in at the top, and the air presses the water down.

(some of the above wording taken from COMMON SCIENCE, NEW-WORLD SCIENCE SERIES Edited by John W. Ritchie)

More in this series at The Common Room Blog

Air Pressure, and Charlotte Mason Science in the early years

Air Pressure: Vacuum Cleaners and Straws

Air Pressure, suction cups, juice cans, and water glasses upside down

Air pressure: eye droppers, canning jars, sea of air, more

syringes, squirt guns, turkey basters

Show that an empty bottle is not truly empty

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