Question

When a dog starts moving, it applies an INTERNAL or mascular force to change its state of rest to motion.But by the first law of motion an EXTERNAL force is necessary to change the state. Explain.

Answer 1

Dear Student ,
When the muscles of the dog applies force on the ground , the ground also gives same external force(normal force)in the opposite direction on the dog which acts as the external force here .Resultantly the dog begins to move .
Hope you understand this .
Regards