# Effective forces on an object for grasping

For example, a robot or a humankind is grasping an object such as a bottle.

Which forces are effective on that bottle ?

This is my opinion:

When we grasp a bottle, we exert a force on contact point. This force can be decomposed into "normal force" and "tangent force". The tangent force points in z-axis. The normal force is perpendicular to the bottle itself.

Normal force creates a friction force on contact point. We can think like there are 3 forces applied on the object in z-axis: Friction force, tangent force, and weight of the object.

<-------- Tangent force . Weight -------->

If weight is bigger than Tangent force, friction force points to right (-->)

If tangent force is bigger than weight, friction force points to left (<--)

<-----------------------------------------------> z-axis

• You can use Newtons method to find a pretty good model...I would suggest just starting with a steel cylinder or square block and reduce down to two contact points of a specific force F like a robot gripper...don't forget decide where your coordinate system is or adding gravity..... See if your methods apply still. – morbo Aug 7 at 17:39