Given:
Someone is lying on the bed.
To find:
A) the internal forces on the mattress
B) The external forces on the mattress
Explanation:
A) The internal forces acting on the mattress are:
1. When someone lies on the mattress, there is tension inside the mattress.
2. There is compression on the mattress.
3. Also there are torsion and shear
B) The external force:
The external forces are the
1. The force of gravity or the weight of the person on the mattress
2. The normal reaction on the mattress
3. The friction between the mattress and the person
