# Free Fall Modeling Activities

Install Ejs and then right-click on a launch node (green arrow) to copy the Free Fall model from this jar file into the Ejs workspace to do the following activities.

## Friction

The Free Fall model assumes that energy is lost only during the floor collision. Set the coefficient of restitution to 1.0 in the model and modify the differential equation to include energy loss due to friction (fluid drag). This energy loss can be modeled by including a friction force Ffriction that is proportional to the velocity:

Ffriction= - b v .

The drag coefficient b depends on the shape of the object and should be included in the model as an additional variable. A good value for simulation is b/m =0.1 although realistic values for objects in air is lower. What is the significance of the negative sign in the friction formula?

## Energy

Add a plot of total energy E(t) to the simple free fall model. Why is the energy plot similar to a plot of radioactive decay? Plots are described in the Ejs manual but note that the Pendulum model in this package includes a plot and can be used as a template for this activity.