An electric motor is a device used to convert electrical energy to mechanical energy. Electric motors are extremely important in modern-day life. They are used in vacuum cleaners, dishwashers, computer printers, machine tools, cars, subway systems, sewage treatment plants, etc, and you can make your own at home! Here’s how:
Coil the wire around a battery about 30 times. Wrap the extended ends of the wire through the coil, securing the coils in place.
Carefully file the enamel off of the bottom half of the extended portion of the wire.
Secure one wire post to each end of the battery, creating a small U-shape to cradle the coil.
Slide a magnet onto the battery.
Place the coil onto the posts and give it an initial spin!
Electricity will flow from the battery through the coil of wire. Moving electricity induces a magnetic field in the coil, which opposes the magnet half of the time, and is attracted the other half. Give it a flick and watch the electrical energy from the battery be converted into the mechanical spinning you see!
Elementary school students the world over are familiar with potato batteries or lemon batteries, but did you know you can make a battery from soda? With just some wire, two different kinds of metals, and your favorite soda, you can build your own battery!
All you need to do is connect your metal plates to one another with a wire (or connect them to a multimeter as well to measure the battery’s voltage like we did) and place your plates into the soda. Make sure your plates aren’t touching during this experiment because if they touch, the electrons won’t flow through the wire and you won’t see a voltage register on the multimeter.
With our battery, the two metals we’re using are zinc and copper, as zinc is more reactive with the soda than the copper is; leading to a more significant voltage produced by the battery. You could also use the aluminum of the soda can, but you would need to remove the coating from the can with steel wool, as it is designed to prevent the aluminum and soda from reacting with one another. You need two different metals because if both plates are reacting with the soda the same amount, there’s no need for electrons to flow between them and therefor very little voltage produced like you see below when we try making a battery with two copper bars.
To understand how the voltage is generated, let’s take a look at the soda itself for a second. Within the soda is phosphoric acid; the key ingredient to this whole process. That phosphoric acid is breaking up into positive hydrogen ions and negative phosphate ions. Those phosphate ions are attracting the positive nuclei of the zinc and copper atoms, but copper holds its atoms together a little better than the zinc. As a result, a lot of electrons from the now separated zinc atoms are left over in the bar, some of which flow through the wire into the copper bar and establish an equilibrium.
The zinc bar is now fairly close to neutral, but the copper is more negative, so it attracts the positive hydrogen ions which remove some of the excess electrons and combine to form hydrogen gas. That gas floats up through the soda and out of the system. This process is happening in a continuous, rapid cycle so electrons are always flowing from the zinc to the copper.
Over time, the copper bar will start to become slightly positive and will repel some of its positive ions into the soda, some of which will encounter the excess electrons on the zinc bar and form a black coating of copper and copper oxide around the zinc. When that has gone on long enough, the zinc in the soda will be completely coated in copper and the voltage will look like our attempt with two copper plates above, eventually killing the battery. When we tried with a different soda, Sprite, the voltage produced was roughly the same, but the battery lasted a lot longer because of the stronger acid in the Sprite. Grab your favorite soda and see how much voltage you can generate!
To start a fire, you need three ingredients: fuel, oxygen, and heat. Friction is a good source of heat (think striking a match, or rubbing two sticks together). Heat can also come from flowing electricity! Have you ever noticed that electronic devices get warm after they’ve been running for a while? This is the result of resistance.
Resistance acts like friction between electrons and the medium they move through. It keeps electricity from moving freely and infinitely, and generates heat as a byproduct. Some substances have lower resistance than others (these are called conductors), but all everyday materials have some resistance.
We can use household supplies to explore this property! On a fireproof surface, hold the business end of a 9v battery up to a pad of steel wool. When a strand of wire touches both terminals, it completes a circuit. Electrons flow through the loop created by the battery and the steel. The wire resists the electrons’ movement and warms up dramatically. We have our heat source, and there’s plenty of oxygen around– but what about fuel?
Steel is mostly made of iron. We know that iron interacts with oxygen. When water is involved, it rusts. When heat is applied, it has the potential to burn. Iron doesn’t catch fire under normal circumstances because its inner molecules are shielded from the surrounding oxygen, but the tiny filaments in steel wool have an enormous surface area per volume. So much iron is exposed to the air that a combustion reaction can start!
So, we have fuel. We have oxygen. We have a heat source. Electrical resistance can start a fire just as well as friction, and with less effort on our part! The spark is easy to create, and it travels quickly along the tiny wires.
An infrared camera shows heat propagating through the steel wool.
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