Which law is best described by the equation F= ka (where F is force measured in N, a is acceleration in m/s², and k is the proportionality constant in kg)

Question

Quizplus · Accepted Answer

Newton's First Law states that a body at rest tends to remain at rest, while a body in motion tends to remain in motion unless other forces are acting on the body.
Another way of saying this is that the motion of the object will remain the same unless something changes it.
This is easy to imagine. If you toss a hockey puck on a frictionless surface like ice it will travel forever (ice is never frictionless in real life though because there are small bumps on the surface). On the other hand, if you put a ball on a flat surface, it will not move until the wind blows it or you hit it.
This can be seen in the equation F=ka. Unless there is a force on an object it will not accelerate. If it does not accelerate it will not change velocity, thus it will stay at rest if at rest and stay in motion (at the same velocity) unless there is a force on the object. This logic can be reversed as well. If the object is changing velocity, then there is a Force acting on the object. Typically this force (on Earth) is gravity and friction so many scenarios are difficult to imagine (because most people have not experienced an environment that is frictionless and devoid of gravity).
Newton's Laws of Motion:
First law: The velocity of a body remains constant unless the body is acted upon by an external force.
Second law: The acceleration (a) of a body is parallel and directly proportional to the net force (F) and inversely proportional to the mass m, i.e., F = ma.
Third law: The mutual forces of action and reaction between two bodies are equal, opposite and collinear

Which Law Is Best Described by the Equation F= Ka