Final answer:
Newton's first law, the law of inertia, states that an object at rest will stay at rest unless acted upon by a net external force, which applies to parked cars. The parking brake should typically be engaged when parked to prevent unintentional movement, though there might be cases where it's not necessary depending on the situation.
Step-by-step explanation:
Application of Newton's First Law to a Parked Car
When considering if Newton's first law applies to a vehicle that is parked, it's important to understand that this law, also known as the law of inertia, states that an object will remain at rest or in uniform motion in a straight line unless acted upon by a net external force.
In the case of a parked car, even though the car is not in motion, Newton's first law still applies. This is because the car will remain parked (at rest) until forces such as the engine starting (providing force to move the car) or an external force such as another car hitting it (which would change its state of rest) act upon it. The act of engaging the parking brake is a preventive measure to ensure that no unintentional forces will cause the car to move, thereby ensuring that Newton's first law maintains the car in its state of rest.
Regarding the use of the parking brake, it is generally advisable to engage it whenever the vehicle is parked. This adds a layer of safety to prevent the car from rolling away due to a mechanical failure or on slopes due to gravity. However, there might be certain conditions, such as specific maintenance or repair situations, or certain flat and secure parking environments, where not applying it could be considered acceptable. The primary concern is the vehicle's safety and preventing any unwanted motion.