Newton's three laws of motion, the F = m × a relationship between force, mass, and acceleration, and why weight is that same formula with acceleration fixed at gravity, the mechanics the HESI A2 physics subtest tests through both scenario and calculation questions.
ObjectiveP.2.1Read4 minExam weightForces and Newton’s Laws ≈ 20% of Physics
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State Newton's three laws of motion and recognise which one a given scenario is demonstrating
Calculate force, mass, or acceleration from F = m × a when the other two values are given
Explain why weight is a special case of F = m × a, using W = m × g, and why mass and weight are not the same quantity
What the lesson concludes
Newton's first law: an object keeps its current motion, at rest or moving at a constant speed and direction, unless a net force acts on it. This resistance to change is inertia, and it scales with mass.
Newton's second law: F = m × a. Force equals mass times acceleration, so a fixed force produces less acceleration on a larger mass.
Newton's third law: every force one object applies to another is met by an equal, opposite force acting back on the first object, not cancelled out on the same object.
A newton (N) is the SI unit of force. One newton accelerates a 1 kilogram mass at 1 metre per second squared, so 1 N = 1 kg·m/s².
Weight is the force of gravity on a mass, W = m × g. With g = 9.8 m/s² on Earth, a 70 kg patient weighs 686 N, even though a change in gravity would change that weight without changing the 70 kg mass at all.