This model illustrates the concept of mechanical work. A brick moves on a plane with friction under the influence of a external force, directed at a certain angle to the surface. Changing the parameters of the model (the mass of the brick m, the factor of friction μ, the absolute value and the direction of the acting force F), one can watch the value of the work, done by the external force and by the force of friction, when the brick moves. Determine in a computer experiment, that the sum of these works is equal to the kinetic energy of the brick. Put your attention to the fact that the work of the force of friction A_{fr} is always negative.