Which equation expresses Newton's Second Law?

Which equation expresses Newton's Second Law?

• A. p = mv
• B. F = m a
• C. E = m c^2
• D. a = F m

Answer: (B)

Newton's second law says that the force acting on an object produces an acceleration that is proportional to the force and inversely proportional to the object's mass. This is captured by the equation F = m a. Think about what that means: if you push harder (larger force) on the same object, it speeds up more, so acceleration goes up in proportion to the force. If the object is heavier (larger mass) while you push with the same force, it doesn’t accelerate as much, so acceleration goes down as mass goes up. The equation encodes exactly this relationship because force is the product of mass and acceleration. Units reinforce this: a Newton (the unit of force) is kg·m/s^2, which matches the right-hand side m a. A rearranged form, a = F/m, expresses the same idea and is equivalent to F = m a, but the specific form with a multiplied by mass would not have the correct units and meaning. Other familiar equations aren’t about forces causing motion: p = mv describes momentum, and E = m c^2 describes energy of mass.

Newton's second law says that the force acting on an object produces an acceleration that is proportional to the force and inversely proportional to the object's mass. This is captured by the equation F = m a.

Think about what that means: if you push harder (larger force) on the same object, it speeds up more, so acceleration goes up in proportion to the force. If the object is heavier (larger mass) while you push with the same force, it doesn’t accelerate as much, so acceleration goes down as mass goes up. The equation encodes exactly this relationship because force is the product of mass and acceleration.

Units reinforce this: a Newton (the unit of force) is kg·m/s^2, which matches the right-hand side m a. A rearranged form, a = F/m, expresses the same idea and is equivalent to F = m a, but the specific form with a multiplied by mass would not have the correct units and meaning.

Other familiar equations aren’t about forces causing motion: p = mv describes momentum, and E = m c^2 describes energy of mass.