Aristotle ’ s fallacy :
Aristotle , the Greek Scientist held the view that an external force is required to keep a body in uniform motion .
His concept is obsolete now , because he considered only one side of motion and fails to explain the other i . e . if body is in motion then how does it come to rest ? There came the concept of the opposing external force of Friction .
For example , a ball rolled on the floor comes to rest after some time due to opposing force of friction .
Conclusion :
An external force is required to keep a body in motion , only if resistive forces ( like frictional & viscous forces ) are present .