MCAT Translational Motion, Forces, Work, and Energy
MCAT Motion and Energy covers classical mechanics — the physics of things moving, being pushed, colliding, and oscillating. This is the single largest MCAT physics topic, accounting for roughly a third of the physics questions on the Chem/Phys section. Expect it in both standalone problems and inside biology passages where a syringe, a contracting muscle, or a beating heart follows the same rules as a block on a ramp.
Most MCAT mechanics questions are application-based, not recall. You will be given a scenario — a car braking, a pendulum swinging, two carts colliding — and asked to extract a quantity or identify a principle. The exam routinely hides what it is actually testing: a question framed as "how far does the block travel" is often really testing whether you will incorrectly use conservation of energy in the presence of friction.
The misconceptions that cost students the most points here are consistent: swapping vectors for scalars (displacement versus distance, momentum versus speed), adding fictitious forces like centrifugal force to free-body diagrams, and dropping the cos-theta factor from work calculations. Newton's third law action-reaction pairs placed on the same object is another classic MCAT physics trap. If your MCAT physics review does not drill free-body diagrams and energy conservation with friction, this area will hurt you.
One-Dimensional Kinematics
The four kinematic equations, plus how graphs of position and velocity encode slope and area differently.
- Confuses displacement (vector, net change) with distance (scalar, total path)
- Assumes average speed always equals the magnitude of average velocity
Two-Dimensional Kinematics and Projectile Motion
Horizontal and vertical motion are independent — range, flight time, and apex behavior follow from that separation.
- Fails to treat x and y axes as independent in projectile motion
- Thinks total velocity is zero at the peak of projectile motion
Newton's Three Laws of Motion
Three laws form the backbone of all force problems; action-reaction pairs and F = ma are the most-tested applications.
- Places action-reaction pair on the same object, incorrectly canceling them
- Confuses Newton's first and second laws by thinking force is needed to sustain motion
Friction (Static and Kinetic)
Static friction varies up to a maximum; kinetic friction is fixed — and neither simply opposes the applied force direction.
- Treats static friction as a fixed value μsN rather than a variable up to that maximum
- Believes kinetic friction exceeds static friction, reversing the μk < μs relationship
Inclined Planes and Free-Body Diagrams
Gravity splits into mg sinθ along the slope and mg cosθ into the surface — swapping them is the classic error.
- Swaps sinθ and cosθ for the parallel and perpendicular gravity components on an incline
- Uses mg instead of mg cosθ for the normal force on an inclined surface
Uniform Circular Motion and Centripetal Force
Centripetal acceleration always points inward; some real force in the problem must be supplying it.
- Treats centrifugal force as a real outward force rather than a non-inertial pseudoforce
- Adds centripetal force as an extra force on the FBD rather than identifying which real force provides it
Torque and Static Equilibrium
Static equilibrium demands both force and torque balance — picking a smart pivot eliminates unknowns instantly.
- Ignores lever arm distance and angle when comparing torques from different forces
- Applies only the force condition for equilibrium, neglecting the torque condition
Work and the Work-Energy Theorem
Work equals force times displacement times cosθ; only net work changes kinetic energy.
- Assumes all forces on a moving object do work, ignoring the cosθ factor
- Treats work as always positive, not recognizing negative work removes kinetic energy
Kinetic and Potential Energy; Conservation of Energy
Energy conservation holds only when friction is absent; spring PE is quadratic, not linear, in displacement.
- Treats gravitational PE as having an absolute value tied to the ground rather than a chosen reference
- Applies conservation of mechanical energy to systems with friction
Power
Rate of doing work — P = Fv is a general instantaneous relationship, not limited to constant-speed situations.
- Conflates total work done with power, ignoring the time component
- Restricts P = Fv to accelerating objects rather than recognizing it as a general instantaneous power formula
Linear Momentum and Impulse
Vector quantity conserved when no net external force acts; impulse equals the change in momentum, not just force.
- Confuses impulse with force magnitude, ignoring the time component
- Treats momentum as a scalar, ignoring its vector nature
Elastic and Inelastic Collisions
Momentum is conserved in every collision; kinetic energy is conserved only in elastic ones.
- Assumes KE conservation applies to all collisions, not just elastic ones
- Thinks perfectly inelastic means all KE is destroyed and objects stop
Simple Machines and Mechanical Advantage
Trade force for distance at constant energy — mechanical advantage and efficiency are not the same quantity.
- Thinks machines can increase both force and displacement simultaneously, violating energy conservation
- Conflates mechanical advantage with efficiency
Universal Gravitation
Gravitational force falls off as 1/r², and orbital mechanics follow directly from setting that force equal to centripetal force.
- Treats gravitational force as inversely proportional to r rather than r²
- Conflates weight (a force dependent on g) with mass (an intrinsic property)
Simple Harmonic Motion (Springs, Pendulums)
Period of a spring depends on mass and stiffness, not amplitude; pendulum period depends on length, not bob mass.
- Thinks larger amplitude means longer period for a spring oscillator
- Incorrectly includes bob mass as a factor in pendulum period
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