What is the diference between a force and a stress?

A force is the amount of load applied, eg 120 lbs

Stress is the area over which the load is applied.

High heeled shoes may dent wooden floors because the load is applied over a small area.  If the heels measure .25sq." (.5 sq." for both combined), then the  force of 120lbs. creates a stress of 120 / (.5 sq. inches) = 250 lbs. per square inch, enough to dent floors!

‚ÄčNails do not puncture the skin because the body weight is evenly distributed over a large surface area.
Do not sit up.