Which formula expresses Newton's Second Law?

Which formula expresses Newton's Second Law?

• A. F_net = ma
• B. F = m v
• C. F = mg
• D. Force is proportional to velocity

Answer: (A)

Newton's second law says that motion changes in response to the total force acting on an object: the net force equals the object's mass times its acceleration. In symbols, F_net = m a. The net force is the vector sum of all forces on the object, and the acceleration points in the same direction as that net force. This rule explains why heavier objects need more force to achieve the same acceleration, and it implies that if there’s no net force, the object moves with constant velocity. The given correct formula captures this general relationship: force is linked to acceleration through mass. The other expressions don’t fit because they either mix up physical quantities or describe special cases. For example, F = m v would equate force to momentum, which has the wrong units and describes a different concept. F = m g gives the gravitational force on a mass in a gravity field, but it’s just one force, not the universal relation between force and motion. Saying force is proportional to velocity incorrectly assigns velocity as the cause of force; it’s acceleration that relates to force, not velocity.

Newton's second law says that motion changes in response to the total force acting on an object: the net force equals the object's mass times its acceleration. In symbols, F_net = m a. The net force is the vector sum of all forces on the object, and the acceleration points in the same direction as that net force. This rule explains why heavier objects need more force to achieve the same acceleration, and it implies that if there’s no net force, the object moves with constant velocity.

The given correct formula captures this general relationship: force is linked to acceleration through mass. The other expressions don’t fit because they either mix up physical quantities or describe special cases. For example, F = m v would equate force to momentum, which has the wrong units and describes a different concept. F = m g gives the gravitational force on a mass in a gravity field, but it’s just one force, not the universal relation between force and motion. Saying force is proportional to velocity incorrectly assigns velocity as the cause of force; it’s acceleration that relates to force, not velocity.