Mechanical vs. Nonmechanical Energy Explained in 2 Physics Videos

Credit: Public Domain

By Andrew Bennett

Energy Conservation in the Real World

We learn early in physics about the Law of Conservation of Energy. Check out my previous post on the topic for a quick refresher on its definition and equations. We also solve a lot of problems that ignore things like friction and air resistance, so our sleds keep sliding and our pendulums keep swinging. Imaginary objects seem to follow the Law of Conservation of Energy quite nicely. However, what about real objects?

When we observe the world around us, we see things slow and stop. A car driving on a flat road can't keep the same speed without more energy from gasoline, diesel, etc. Balls don't bounce as high the second time. A child on a swing slows down without being pushed or pumping their legs.

Do these examples violate the Law of Conservation of Energy? Of course not!

Mechanical and Nonmechanical Energy Video

In this video, we review various energy types. Mechanical energy usually is pretty obvious – the ball is up high, the bullet is moving fast, etc. Nonmechanical energy often is invisible. We can't see the thermal energy that friction generates or the gasoline's chemical energy that becomes the car's kinetic energy.

This video reviews the types of energy. Then, it discusses the energy transformations that occur as a person sleds down a hill. By focusing on both mechanical and nonmechanical energy, we see that this motion doesn't violate any physics laws.

How Are Friction and Thermal Energy Related?

What Is Friction?

Friction is a force that resists the sliding of two surfaces past each other. But what causes it?  Simply put: Everything is bumpy. When one surface slides past another, the bumps on the two surfaces catch on each other.

What Is Thermal Energy?

Thermal energy is the energy in a system related to temperature. More basically, it is the kinetic energy of individual atoms. Atoms are always moving, and how much they move (how much kinetic energy they have) is experienced as the temperature of the object. Almost every time energy transfers from one form to another, it results in some thermal energy. 

Friction causes the conversion of a portion of mechanical energy into thermal energy (heat) because whenever those bumps on the surfaces catch, there is a tiny collision that causes the atoms of the bumps to jiggle a bit more than before. This means more energy is thermal energy and less energy is in other forms.

How Friction Affects Stopping Distance 

In this video, we combine what we know about friction, work, and energy conservation to solve a physics problem about how far a child on a sled will go on a flat area after a hill of known height given a certain amount of friction.

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