In this lesson our instructor talks about gravitational potential energy. First, he discusses why it is called potential energy. Then he gives an introduction to gravitational potential energy. Lastly, he talks about conservation of energy. Four complete example problems round up this lesson.
We can think of potential energy as energy stored for future use. This isn't perfectly rigorous, but it gives us a good understanding for now.
The amount of gravitational potential energy is based off of the mass of the object, the gravity involved, and the height of the object:
Egravity = mgh.
We have to set the "base" height. Remember, as usual, we're the ones who have to impose a coordinate system, so it's up to us to determine what we consider the starting height.
Because of this, the important thing isn't the "absolute" height, but instead the relative height between the start and end heights: ∆h.
This formula relies on the fact that g is a constant near the surface of Earth (or whatever gravitational body we're dealing with). If g were to vary over the height traveled, we would need a different formula.
By the conservation of energy, we can look at the entire energy of the system at the start and end:
Esys, start + W = Esys, end.
[Remember, positive work puts energy into the system, while negative work takes it out.]
It's up to decide when we want to take our start and end "snapshots." Carefully choosing what moments we want to compare is key to solving problems.
Energy: Gravitational Potential
Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.
This book includes a set of features such as Analyzing-Multiple-Concept Problems, Check Your Understanding, Concepts & Calculations, and Concepts at a Glance. This helps the reader to first identify the physics concepts, then associate the appropriate mathematical equations, and finally to work out an algebraic solution.