How to judge the direction of the elastic force of the spring

The direction of the elastic force of the spring is mainly determined by the deformation direction of the spring. The direction of the elastic force is opposite to the direction of the deformation of the object, and acts on the object that forces the object to deform. Specifically:

The direction of the elastic force at both ends of the spring: coincides with the central axis of the spring and points to the direction in which the spring returns to its original state.
The direction of the elastic force of the light rope on the object: along the rope, pointing to the direction of the rope contraction.
The direction of the elastic force of the surface-to-surface contact: perpendicular to the contact surface and pointing to the object under force.
The direction of the elastic force of the point-to-surface contact: perpendicular to the contact surface (or the tangent of the contact surface) through the contact point, pointing to the object under force.
The direction of the elastic force of the ball-to-surface contact: on the line connecting the contact point and the center of the ball, pointing to the object under force.
The direction of the elastic force of the ball-to-ball contact: perpendicular to the common tangent plane through the contact point, through the centers of the two balls and pointing to the object under force.
Specific judgment method
Judgment based on the direction of deformation of the object: the direction of the elastic force on the object is opposite to the deformation direction of the object applying the force. For example, if a spring is stretched, the direction of the elastic force is opposite to the stretching direction. ‌
‌Judge based on the direction of the external force that causes the object to deform‌: The direction of the elastic force is opposite to the direction of the external force that acts on the object to deform the object. For example, if the spring is stretched by gravity, the direction of the elastic force is opposite to the direction of gravity.
‌Judge based on the movement of the object‌: Use the equilibrium condition (or dynamic law) of the object to judge. For example, if the object is in equilibrium, the direction of the elastic force can be determined by the two-force equilibrium condition. ‌
Example analysis ‌A small ball is hung at the bottom of the hanging spring‌: For the small ball, the elastic force (the pull of the spring on the small ball) is vertically upward; for the spring, the elastic force (the pull of the small ball on the spring) is vertically downward. ‌
‌A spring is placed vertically on the table with an object on it‌: If the length of the spring is greater than the original length, the elastic force of the spring on the object is manifested as a downward pulling force; if the length of the spring is less than the original length, the elastic force of the spring on the object is manifested as an upward supporting force.