Final answer:
Newton's first law, the law of inertia, explains that a vehicle will remain at rest or move at a constant velocity unless acted on by a net external force. This law applies to vehicles either stationary or in motion, where forces such as engine thrust, friction, and air resistance come to play.
Step-by-step explanation:
Newtons's first law, often referred to as the law of inertia, states that a body at rest remains at rest, or if it is in motion, it continues to move at a constant velocity unless acted upon by a net external force. This principle can be observed in everyday life, such as the movement of a vehicle. When a car is parked, the only forces acting upon it are gravitational force pulling down and the contact force from the ground pushing up, resulting in no net force and thus no movement as per Newton's first law.
If the car is moving at a constant velocity, it implies that the driving force of the engine is balanced by friction and air resistance. The car continues to move in a straight line until a force, such as the brakes or a turn of the wheel, causes acceleration or deceleration, changing the car's state of motion in accordance with Newton's first law.
For example, if you're driving at 50 km/hr and there are no external forces like friction or air drag, your car would maintain that speed and direction indefinitely. However, in reality, forces like friction and air resistance are always acting upon the vehicle, necessitating the use of the engine to maintain constant speed.