Newton’s Laws and the Physics of Motion
Isaac Newton published his three laws of motion in 1687, in a work titled Philosophiæ Naturalis Principia Mathematica, and MCAT physics questions on force, motion, and equilibrium still trace directly back to that text more than three centuries later. The first law — an object at rest stays at rest, and an object in motion stays in motion, unless acted on by an unbalanced force — formalized an idea Galileo Galilei had already begun exploring decades earlier through inclined-plane experiments, overturning the ancient Aristotelian assumption that objects naturally came to rest without a force keeping them moving. Newton’s second law, force equals mass times acceleration, gave that intuition a precise mathematical relationship, while the third law — for every action there is an equal and opposite reaction — explains everything from how a swimmer pushes off a pool wall to how a rocket generates thrust by expelling exhaust in the opposite direction.
Torque, equilibrium, and center of mass — concepts the MCAT tests through problems involving levers, joints, and rotating systems — are direct extensions of those same three laws applied to rotational rather than linear motion. A system is in translational equilibrium when the net force acting on it is zero, and in rotational equilibrium when the net torque is zero; both conditions can hold simultaneously, which is exactly the physics underlying how the human forearm functions as a lever system around the elbow joint, a favorite MCAT passage topic that connects Newtonian mechanics directly to anatomy.
Fluids, Circuits, and the Physics Hidden in the Body
Fluid mechanics on the MCAT draws heavily on two 18th- and 19th-century principles. Blaise Pascal’s 1653 principle — pressure applied to an enclosed fluid transmits equally in all directions — explains hydraulic systems and underlies how blood pressure propagates through a closed circulatory system. Daniel Bernoulli’s 1738 work established that within a flowing fluid, pressure decreases as velocity increases, a relationship that explains why blood flow speeds up and pressure drops as it moves through a narrowed blood vessel, and why measuring blood pressure at different points in the circulatory system yields different readings depending on vessel diameter and flow rate.
Electric circuits round out the physics section, with German physicist Georg Ohm’s 1827 law — voltage equals current times resistance — providing the mathematical foundation for every series and parallel circuit problem the exam includes. Ohm’s law wasn’t well received initially; it contradicted a prevailing, more philosophical German approach to physics at the time, and Ohm was passed over for academic positions for years before the law’s practical usefulness became undeniable. The same current-voltage-resistance relationship Ohm formalized also underlies how nerve cells generate and propagate electrical signals, connecting the MCAT’s physics content directly back to the biology and physiology tested elsewhere on the exam — a reminder that the exam’s four sections were never meant to be studied in complete isolation from one another.
Sound and wave behavior round out the section’s remaining core topics, built on nineteenth-century work by physicist Christian Doppler, who described in 1842 how a wave’s observed frequency shifts depending on the relative motion between its source and an observer — the same Doppler effect that lets modern ultrasound equipment measure blood flow velocity by detecting the frequency shift in sound waves reflecting off moving red blood cells, a direct, centuries-later application of a principle Doppler originally developed to explain the color of binary stars.
Source: National Institutes of Health (NIH) and Encyclopaedia Britannica.