Q: How do we know what type of energy the problem is talking about? I don’t really understand the difference between Kinetic, Mechanical, Conservative, Potential Energy’s difference other than they have different equations. I’m confused about how to determine the differences in the types of energy and how to know which one to solve for in a problem.
A: In general, Energy is an ability to do Work! Different types of energy are associated with different ways to do work. Kinetic energy is associated with motion and can drive forces, like contact force, gravity force, to do work (transform to other types of energy). Potential energy is associated with a specific conservative force, like gravity. Mechanical energy is just the sum of the above two. In a problem, analyze the process and identify the forces or work done by forces. Then find the energy associated and pick appropriate equations to solve it.
Q: Can an object that is in motion have zero potential energy and zero kinetic energy? If so then how can it be moving.
A: The short answer is “Yes”. Kinetic energy is an “absolute” energy which can only be positive or zero, but potential energy is a “relative” energy which could be positive, zero, or negative. If in a motion with mechanical energy conserved, it is possible that at a position the object has zero potential energy and zero kinetic energy. It will then move toward another position where potential energy is negative and kinetic energy is positive. For example, a rock is dropped from rest from a height. Define the potential energy is zero at the initial position.
Q: Relating Mechanical Energy (Potential and Kinetic Energy) to Chemistry Regarding bonding chemistry between molecules, what is true of the potential energy and kinetic energy of the bonding electrons when the bond between 2 molecules breaks?
A: As far as I know, the Chemical bond is a type of binding associated with electric potential energy of microscopic particles with charges (covered in E&M). A steady bond has negative potential energy usually. To break the bond, some other types of energy are supplied or work is done to increase the potential energy from negative to zero. When potential energy becomes zero, two particles are considered having no influence on each other, in other words, no bond!
Q: How often are collisions considered completely elastic? What are some common real-world examples of inelastic and elastic collisions? Do we see one happen more than the other? Why is that?
A: Most collisions are actually something else between Completely Elastic and Perfectly Inelastic. Completely Elastic collision requires both Momentum conservation and Mechanical Energy conservation, so it is even less popular than Perfectly Inelastic. A typical example of Completely Elastic collision is collisions between Billiard/Pool balls. Perfectly Inelastic collision is more common, for example, collisions of cars in an accident.
