Guitar Straps
When a guitar strap is used, there is tension present in the strap. That tension is able to resist the force of gravity, keeping the guitar from falling to the ground. However, the strap must stay attached to the guitar for it to work properly.
In addition to tension, when a guitarist wears the guitar strap, the guitarist experiences a normal force. This normal force is between the guitar strap and the guitarist, and between the guitar and the guitarist.