1- Select and play the visual in the following situations:

Blue object: F = 10 N,  GREEN object: F = 10 N, angle = 0º, Ice.

Blue object: F = 10 N,  GREEN object: F = 10 N, angle = 0º, Clay.

BLUE object: F = 10 N,  GREEN object: F = 10 N, angle = 0º, Sand.

Does the friction (Fr) do any work?

What is the meaning of the work assigned to friction in the visual (W_Fr), then?

2- Find a force F applied to the GREEN object on Sand that is able to do the same work,

W, as the force F = 5 N applied to the BLUE object, in the same time. 

How does friction influence the effectivity of work?

3- Find out the distance covered by the GREEN object (clay surface) when a force of 8 N is applied to it in such a way that it will do the same work as the BLUE object subjected to a force of 8N   with the distance set to 5 m.