Introduction: Hand Pump!
The literal hand pump!
With nothing but a tube and science on your side, you can make water climb skyward. This is a quickie and requires almost no set-up, but is a great introduction to so many fundamentals of motion like adhesion, cohesion, friction, air pressure, and gravity. It's also just plain fun.
Learn the technique and you'll learn pure joy.
- What: A Literal Hand Pump
- Cost: ~$5 for a tube
- Time: ~2 minutes to set up
- Concepts: pressure, friction, inertia, surface tension, adhesion, cohesion
- Firm plastic tube (starting with 1" diameter at 3' is good, then go up and down from there)
- Food coloring (optional)
Let's pump it up!
Step 1: Fill a Bucket
Looking good so far!
Fill up a fairly deep bucket about 3/4 full with water. Special bonus if you tilt the nozzle to the side to make a whirling current to add the food coloring in. Mix it with your hand or a tube to make a colorful pool.
Step 2: Climb, Water, Climb!
Simply place one hand on top of the tube, and one hand on the side. You'll need to be able to cover the diameter of the tube with the palm of your hand. This technique is reliant on a bunch of things including adhesion, cohesion, pressure, and inertia.
It takes a bit to figure it out, but once you get the feel, you won't forget it. Your supporting hand is going to be rocking the tube up and down. Your upper hand is being held somewhat firmly against the top, but you will feel the pump action. Your hand seals the tube when you raise it, pulling water upward and sealed, and then it slightly unseals as you move the tube down to pull more water up.
Mapping the motion is actually pretty amazing, and a challenge to figure out. Take a couple shakes and see if you can raise the water level even just a bit. After not too long, you'll be able to pull it out the top of the tube.
Another thing to notice is how the feeling changes as the water level rises. As you get a larger and larger slug of water moving up and down, the suction becomes more intense.
Step 3: The Release
After a job well done, it's time to let go.
This tube is like a giant version of what happens when you suck water into a straw and hold it. Except with a straw, when your finger goes over the end, the surface tension of the water on bottom plus the seal is great enough to overcome gravity and keep the water from falling.
In this case, the water "splits" apart in the middle and moves along the sides of the tube as a curved bubble moves upward through the column. It's beautiful.
If you take your hand off, the whole plug of water will suddenly drop as air pressure returns to push it down.
Step 4: Try Other Sizes!
Different diameters make for very different results. The skinny tube can be done with a single finger and a the medium sized one allows to pull a large amount of water up really quickly. After you're done with this, go on to try to make a different kind of pump. Neatly, they all fundamentally work in this same way.
Have fun, get soaked, and keep exploring. :)
Let me know when you master the technique!