# Bullet Physics: Applying a force at the point of collision

Suppose I want to simulate some kind of gripper with two "fingers" (such as pair of pliers, or two-fingered robot hand), picking up an object from the ground. Both the gripper and the object are dynamic rigid bodies.

I want to start with the object roughly in the centre of the gripper, and then move the two fingers towards the object, to determine the point at which they make contact with the object's surface. Then, I want to apply a certain force from the fingers onto the object, before finally lifting the fingers (and hence the object) upwards.

Is there any simple way to achieve this just by treating the two fingers as two individual rigid bodies? I want to just move the fingers towards the object to find the point of collision -- so can I treat them as kinematic objects (with zero mass so they don't fall under gravity, which is what I want), and move them manually by slowly changing the pose of each finger over time? But how will I know at what point the fingers and object collide, so that I should stop moving the fingers and start applying a force?

Thank you!