### Why are Energy Models Important?

Energy Models shift the focus from the cyclist to the cycle. In some scenarios, it is easier to track the cycle energy changes than it is to work through all of the equations. These scenarios include descents, speed changes, and coasting.

### Speed Changes

We have already discussed Cycle Energy. So what we will do is increase your speed to 18 mph. Your combined CyclistCycle Weight is 186 lbs. How much work must you do in Joules to make the change in inertial motion?

Work = KEFinal – KineticEnergyInitial

Work = ½mVf ² – ½mVi ² = ½m(Vf ² – Vi ²)

Since we want our answer in Joules, we convert to metric values

m = 84.368 kgs

Vi= 6.7056 mps Vf= 8.046 mps

This tells us the change in speed requires 834.6 Joules. Now suppose I want to make the speed change in 15 seconds, what must my power output be?

P = 834.60/15 = 55.64 Watts

Next Topic: Longitudinal Dynamics