Question

What do you understand by external and internal forces ?​

Answer 1

Internal forces: The forces that enamate from inside within a system .The system must be defined by you.

External forces:The forces that enamate from outside within a system.

Answer 2

External forces are forces caused by external agent outside of the system. Internal forces are forces exchanged by the objects in the system. To determine what part should be considered external and internal, mechanical system should be clearly defined.