### 7. Ohm's law

Let's imagine the ball again. If you have a small ball travelling at a very high speed, it could potentially have as much or more power as a large ball travelling at a very low speed. In this way, you could say there is a direct relationship between the speed a ball is travelling, the size of the ball, and the potential power of the ball.

Of course though, we are actually not really talking about balls, but electricity. When dealing with electricity, voltage and current are in a direct relationship with power. In a circuit, power is expressed in terms of Watts. The symbol for this is a W.

Watts = Voltage * Current

There is also another factor we have yet to talk about that also plays a role, and that is resistance. In our analogy, resistance is the headwind that the ball must fight against to move forwards. On a calm day, there might be little resistance to its flight, but on a windy day, it might have to fight against the wind pretty hard. Again, we are actually talking about electrical resistance in a circuit and not throwing a ball.

Resistance pushes against the flow of electricity. As such, it is also in direct relationship with Watts, Voltage and Current. Resistance is expressed in Ohms (after it's discoverer). This mathematical relationship between Watts, Voltage, Current and Resistance is unsurprisingly called Ohm's Law.

Ohm's Law is not something you must memorize, but it will play an important role later when determining how much resistance a circuit must have. Thanks to this law, a circuit having a minimum amount of resistance is not optional, but necessary. The energy in the circuit must encounter resistance in order to expend itself. The thing in the circuit which uses energy is considered the Load. If an electrical supply is connected to ground without a load to use up the energy, bad things will happen.

##### You should NEVER connect your positive voltage source directly to ground.

One of the other fundamental concepts of Ohm's Law is that electricity must encounter a minimum amount of resistance in a circuit and be able to expend itself. If you connect power and ground directly together, there will be a lot of energy that has no way of expending itself. Your circuit will then try to release this unused energy in highly antisocial ways. Basically, the energy will turn into heat. However, having nothing in particular to warm, either your power source or wire will start to dramatically heat up. This can potentially result in a damaged power supply, melted wire, a fire, or potentially an explosion.

Another name of this phenomena is a "short circuit." You likely have heard this term before.