Lesson 2: Energy — The Currency of the Universe
Energy — The Currency of the Universe
Energy is the ability to make things happen. Everything that occurs in the universe involves energy changing from one form to another.
Types of Energy
Kinetic Energy — energy of motion. A moving car, a thrown ball, a flowing river. The faster something moves or the heavier it is, the more kinetic energy it has. Formula: KE = ½mv²
Notice the velocity is squared. Double your speed and you have 4× the kinetic energy. This is why highway crashes are so much more deadly than parking lot fender-benders.
Potential Energy — stored energy waiting to be released. A rock on a cliff has gravitational potential energy. A stretched rubber band has elastic potential energy. A battery has chemical potential energy.
The Big Rule: Energy is Never Created or Destroyed. It only converts from one form to another. This is the Law of Conservation of Energy — one of the most important laws in all of physics.
The Roller Coaster
A roller coaster is a perfect energy converter. At the top of the first hill, you have maximum potential energy and minimum kinetic energy (you're barely moving). As you drop, potential energy converts to kinetic energy — you speed up. At the bottom you're going fastest. As you climb the next hill, kinetic converts back to potential. You slow down.
Why is the first hill always the tallest? Because some energy is lost to friction and air resistance (converted to heat) on every hill. You never have enough energy to get higher than where you started.
Power vs Energy
Energy is how much work gets done. Power is how fast it gets done. A strong person and a weak person climbing the same stairs use the same energy — but the strong person gets there faster, so they use more power.
Power is measured in watts. A 100-watt lightbulb uses 100 joules of energy every second.
Think About It
- A pendulum swings back and forth forever in your imagination but slows down in real life. Where does the energy go?
- Why do electric cars recover energy when braking?
- Food has calories — which type of energy is that?