Why Does Ladder Slipping Depend on the Ground's Surface?

[brad sue]

Hi,
I need some explanation about a problem:

A heavy man stands on a ladder that is leaning against a rough-surfaced wall and rests on the ground. Dranw the free-body diagram for the system of the man and the ladder. If the ground is very smooth, the ladder may stast to slip. Why.

I need some explantions for the WHY question .

Thanks

 

[HallsofIvy]

Explanation of WHAT? Do you know what a "free-body" diagram is? Can you determine the various forces acting here? What are the forces on the man? What are the forces on the ladder?

 

[brad sue]

Explanation of WHAT? Do you know what a "free-body" diagram is? Can you determine the various forces acting here? What are the forces on the man? What are the forces on the ladder?

Yes, I found the forces on the man and on the ladder.
On the man there is only the gravity.

On the ladder, on the botton I have the reaction with the ground and a friction force directed toward the wall. On the top of the ladder, there are a reaction force coming out the wall and a vertical friction force.

I need explantion why the ladder starts to slip if the ground is very smooth.