In a hydroelectric power plant, energy changes happen in a few important steps:

1. From Potential Energy to Kinetic Energy:

   • Water stored in a reservoir has potential energy because it is high up. For example, if a reservoir is 100 meters above ground, it has a lot of energy. We can figure out potential energy ($PE$) using this formula:
   $$PE = mgh$$

   Here, $m$ is the weight of the water, $g$ is the force of gravity (which is about $9.81 \, \text{m/s}^2$), and $h$ is the height.

2. From Kinetic Energy to Mechanical Energy:

   • When the water flows down, its potential energy changes into kinetic energy ($KE$). This moving water spins the blades of a turbine, turning the flow of water into energy that makes the turbine rotate.

3. From Mechanical Energy to Electrical Energy:

   • The turbine is linked to a generator. As the turbine spins, it makes the generator work. This process changes the mechanical energy into electrical energy using something called electromagnetic induction. A hydroelectric power station can produce between 100 megawatts (MW) and over 10,000 MW of electrical power.

4. From Electricity to Use:

   • The electrical energy created is sent through power lines to homes and businesses, allowing people to use the energy.

In summary, hydroelectric power plants use the energy from gravity and turn it into electrical energy. They do this very well, with around 90% efficiency!