Homopolar motor. Photo Credit: leventsakar.net
Electric motors are used in many applications from robotics to children’s toys. Although many of these motors are DC motors, Homopolar motors are the simplest of motors and are easy to show students in a classroom setting. All it takes to build your first simple motor are three common materials you can probably find around the house: copper wire, a AA battery, and neodymium magnets.
Common heart shaped approach. Photo Credit: electronics-micros.com
Constructing the motor is simple but getting it to work can take trial and error as well as a bit of patience. Here’s how to do it:
1) Attach the magnet to the negative side of the battery.
2) Strip the copper wire completely or for safety, in the middle and at the two ends.
3) Bend the wire so that one end touches the positive terminal and the other end touches the magnet. A common approach is a heart shaped wire for better stability.
4) Watch: As the copper wire touches the magnet, the wire will begin to spin.
Current (blue) flows from the positive terminal to the magnet at the negative terminal. The current flows in the presence of a magnetic field (red). This causes a force perpendicular to those directions (in the page on the left of the battery and out of the page to the right of the battery). This force causes the wire to spin. Photo Credit: Physics Central
How does it work? Well the theory can get as detailed as you want it to be but to keeps things simple, I will explain the homopolar motor briefly. The copper wire connects the positive terminal to the magnet at the negative terminal. This completes the circuit, allowing current to flow through the circuit (and the wire). Due to the magnet, the current is flowing in the presence of a magnetic field around the battery. When current flows in a magnetic field, it will experience a force called the Lorentz force. This force acts perpendicular to the magnetic field and the flow of the current (and the wire). Consequently, the perpendicular force pushes the wire around the battery.
Once you get a working motor, you can change the shape of the wire to any shape you want! Have fun!
Until next time…
We’ve all been taught that water freezes at 32F (0C) but in actuality water can remain liquid below this temperature, under special conditions. Imagine you’re sitting on your couch after a long day, you’re tired and you’re starting to feel a bit hungry, but the fridge is so far away. Eventually you get hungry enough to get up, go to the fridge, and satisfy your hunger. Water can relate. When the temperature of the water drops below 32F it would prefer to be a solid, but it takes energy to change from a liquid to a solid. As the temperature gets lower the water gets “hungrier”, it wants to be a solid even more, eventually it wants to be a solid enough to overcome the energy barrier, the “walk to the fridge”.
When water wants to become a solid there are two ways it can go. It can either grow on a surface, like condensation on a cool drink or around a dust particle like rain, or, if it has enough energy, it can grow little spheres of solid within the liquid, without the help of a surface. The amount of energy required for this phase transformation is directly related to the amount of surface created. When the transformation is happening on, say the inside surface of a water bottle, the liquid only has to support the area of a dome, the bottle takes care of the rest. When there is no bottle to work with, or the liquid is far from the surface of the bottle, it has to have enough energy to support the surface area of a whole sphere.
If you’re trying to replicate the video above it’s crucial to have very clean water. This means there are no little particles that the water can use to lower the amount of energy required to freeze, it has to save up enough to grow the spheres without any help. The water also needs to be cooled slowly and handled gently because any significant energy changes, thermal or kinetic, can give the water enough energy to start freezing. This is why hitting the bottle will start the reaction. When the bottle is hit, it finally gets the “oomph” it needs to get to the fridge (freeze).
These phenomena (heterogeneous and homogenous nucleation) are also responsible for the famous Mentos and Coke experiment, why bubbles in carbonated drinks seem to come from specific points in the glass, and how engineers make aircraft aluminum strong enough to keep planes in the sky.
Olive trees. Photo Credit: bymovement.com
Note: Due to miscommunication, this post was submitted late and thus scheduled late; rest assured, regular scheduling will resume on Sunday.
Back at my parent’s house in North County San Diego we have a lot of olive trees and every year they drop their fruit on the ground and make quite a mess. There is no sense in letting all of these olives go to waste so I looked into ways to turn them into a usable oil. It was surprisingly simple, just follow a few steps.
First the harvest. The olives are pretty small and there are a lot of them all over the tree making it way too labor intensive to pick by hand. The simplest way to do it is to lay a tarp on the ground, get a ladder and comb the branches with a garden fork or rake. Let the olives and leaves fall on the tarp then collect them all and pick the olives out.
Now that you’ve got a good amount of olives you’ve got to get the oil out of them. This is where industrial manufacturers use massive hammer mills and centrifuges. That’s a bit of an overkill for home production. First you need to crush the olives, to do this you can just get a strong bag, fill it with olives and go at it with a hammer. I tried a meat grinder and it worked OK but the pits jammed up the machine, a bag and hammer wont have that problem!
Once you have a pretty good pulp of olives you’ve got to mix them so that the oil can form large enough droplets to be pressed out. Don’t mix for much longer than 15 min because you’re adding oxygen to the oil and that will give it an undesirable flavor and color, but if you mix much less than that the oil won’t form large enough droplets.
Now for the pressing. It takes quite a lot of pressure to get the most out of this olive paste so I got a 20 ton bottle jack for a car, built a frame with a two plates and used the jack to press the olives. First spread the paste on burlap or cheese cloth, really any porous fabric that will allow the solids to stay in place and the liquids to flow. Then fold up the cloth, put it in the press and press. Collect all the liquid that comes out and pour it into bottles.
The liquid in the bottles will be about 90% water and 10% olive oil. Leave these bottles in a cool dark place for several weeks to give the oil plenty of time to settle out then pour off the oil on top and store for later, or enjoy now. It will taste very different from store bought oil, in a great way!