Gravity and Conservative Forces

What makes gravity special?

From the perspective of the universe, gravity is extremely weak, but also its sculptor. From the perspective of a cyclist, gravity is not weak and is important to riding.

In Physics, Gravity is one of a select group of forces called Conservative. As a cyclist, it is important to understand what this means.

What makes a force conservative?

Gravity is what is called a field. It has a value and direction at every point in space.This is different from a force such as rolling resistance where it is applied at a specific point.  When we are cycling, we are moving through the field effectively “experiencing” its value at each point along our path.

Conservative Vector Fields are important because they have three key features critical to cyclists:

  • What goes up, must come down.
  • Don’t care how you get here, just get here
  • You have potential to do great things

What goes up, must come down.

Throw a ball straight up, and it comes back to you. Ride to the top of hill, and you can coast back down. Conservative forces are such if you move an object against it, the force will then return the favor and pull it back to you.

For cyclists, this is a key process to ascents and descents, and results from gravity always pulling in the same direction.  When you are going up, you are working against gravity. Once you are up, gravity is working for you.

Just Get Here

We know that effort is quantified as work and measured by multiplying force times distance. In climbing, we know various stretches have different slopes so that some are harder than others.

But when you are dealing with gravity, the number of segments and different ways to get to the top do not make any difference in the final result. The total effort against gravity to get from the bottom to the top will be the same and is equal to the CyclistCycle Weight times the Elevation Gain.

You have potential

The more you work against gravity, the greater your potential to get back. In Physics, this is quantified as potential energy and it is created when an object is moved from one location to a higher location. At any given point, we can use it, or not to meaning we have the potential to use it later.

In cycling, we say that we have stored energy in the cyclist-cycle in moving it to a higher location. How much energy is easily calculated:

Potential Energy = Weight * Elevation Change

But this is also important for another reason. In order to move an object from one location to another, you must perform work to do so. Work performed against gravity is conserved in the sense that it increases potential energy by an equal amount. So when you reach your final location, the total work performed against gravity is exactly equal the increase in the potential. What this means is that if you are making a climb with a given elevation gain, the total work you need to perform is the difference between the potential energy at the start and at the finish is equal to the total work effort that must be performed.

Next Topic:   Slopes and Gradients


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