Which of the following is/are true about the frictional force?
1. It acts between all moving objects.
2. It always opposes relative motion between two objects.
3. It is a contact force.
4. It is a non- contact force.
2, 3 and 4
Friction is a force that opposes the relative motion between two objects. Since two surfaces need to be in contact, for friction to come into action, it is a contact force. It depends on the nature of surfaces in contact. It is more for rough surfaces.