First law

• If the resultant force on a stationary object is zero, the object will remain stationary.
• If the resultant force on a moving object is zero, it'll just carry on moving at the same velocity.
• Newton's first law is basically just saying a resultant force is required to change the motion of an object!
• When a train/bus/car is moving at a constant velocity, the resistive and driving forces on it must be balanced. The velocity will only change if there is a non-zero resultant force.
• The tendency of an object to continue in its current state (at rest or in uniform motion) is called inertia.