'Consider the motion of a car starting from rest, picking up speed and then moving on a smooth straight road with uniform velocity (Fig.). It moves as it accelerates. This must be due to some net external force. It has to be an external force. The acceleration of the car cannot be accounted for by any internal force.' What does these lines mean?
Dear Student,
A body can't move by itself as the internal force cancel out each other when they are applied on different parts of the body.
So a body moves only when the net force on the body is not zero, that is possible only in the case of external force.
So there has to be some external force for a body to move.
This force is friction. Friction forces a body to move in forward direction.
Regards
A body can't move by itself as the internal force cancel out each other when they are applied on different parts of the body.
So a body moves only when the net force on the body is not zero, that is possible only in the case of external force.
So there has to be some external force for a body to move.
This force is friction. Friction forces a body to move in forward direction.
Regards