MCAT kinematics and forces describe how objects move and why. Kinematics is the bookkeeping of motion — position, velocity, and acceleration — while Newton’s laws explain the forces behind it. Together they are the foundation of the physics section, and the free-body-diagram habit you build here carries into fluids, circuits, and beyond.
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update Updated October 2026
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bolt The 60-second version
check_circleKinematics relates displacement, velocity, acceleration, and time; the four equations assume constant acceleration.
check_circleIn projectile motion, horizontal and vertical components are independent; vₓ is constant and v_y changes with g.
check_circleNewton’s second law, F = ma, is the workhorse — always start from a free-body diagram.
check_circleOn an incline, weight splits into mg·sinθ (down the ramp) and mg·cosθ (into the ramp).
check_circleNormal force is not always equal to weight — it depends on the other vertical forces.
check_circleStatic friction can vary up to a maximum; kinetic friction is roughly constant while sliding.
target What you'll be able to do · aligned to AAMC content category 4A
4AApply the kinematic equations to one-dimensional and projectile motion.
4AState and use Newton’s three laws to relate force, mass, and acceleration.
4ADraw free-body diagrams and resolve forces into components on inclined planes.
4AAnalyze friction, tension, and normal forces in equilibrium and accelerating systems.
How the MCAT tests kinematics and forces
This material anchors AAMC content category 4A — translational motion, forces, work, and energy in living systems. The MCAT emphasizes setting up problems correctly: choosing the right kinematic equation, drawing a clean free-body diagram, and resolving vectors. Careful setup beats memorized formulas.
workspace_premium The universal first step
Almost every mechanics problem starts the same way: draw the free-body diagram, pick axes, and apply F = ma along each axis. Set that up correctly and the algebra follows.
The kinematic equations
For constant acceleration, four equations connect displacement (x), initial and final velocity (v₀, v), acceleration (a), and time (t). Pick the one that omits the variable you neither know nor want.
v = v₀ + atNo displacementRelates velocity and time directly through acceleration.
x = v₀t + ½at²No final velocityGives displacement from initial velocity, acceleration, and time.
v² = v₀² + 2axNo timeThe go-to when time is neither given nor asked for.
Projectile motion
A projectile moves under gravity alone. The key insight is that the horizontal and vertical motions are completely independent and share only the time.
Projectile motion. Horizontal velocity vₓ stays constant; vertical velocity v_y decreases going up, is zero at the apex, and increases coming down.
Horizontal: no acceleration, so x = vₓt (constant velocity).
Vertical: acceleration = −g, so treat it as free fall.
At the peak, v_y = 0 but vₓ is unchanged, so the object is still moving horizontally.
Newton’s laws of motion
Newton’s three laws connect force to motion and are the backbone of every mechanics problem.
First law (inertia): an object keeps its velocity unless a net force acts on it.
Second law: F_net = ma — net force produces acceleration in the same direction.
Third law: forces come in equal and opposite pairs acting on different objects.
F_net = maNewton’s second lawSum the forces along each axis and set equal to mass times acceleration. In equilibrium, a = 0 and forces balance.
Free-body diagrams and inclined planes
A free-body diagram isolates one object and draws every force acting on it. On an inclined plane, tilt your axes to align with the ramp so gravity is the only force you have to resolve.
Block on an incline. Weight (mg) points straight down; the normal force (N) is perpendicular to the surface; friction (f) acts along it. Gravity resolves into mg·sinθ down the ramp and mg·cosθ into it.
functions Worked example — acceleration down a frictionless incline
A block slides down a frictionless 30° incline. What is its acceleration? (g = 10 m/s²)
Along the ramp, the only force is the gravity component mg·sinθ.
Newton’s second law along the ramp: ma = mg·sinθ, so a = g·sinθ.
a = 10 · sin30° = 10 · 0.5 = 5 m/s².
Answer. a = 5 m/s² down the ramp — mass cancels, so it does not matter.
Friction, tension, and the normal force
Three contact forces recur constantly. Getting their directions and magnitudes right is most of the battle.
Reading motion graphs. On a velocity–time graph, the slope is acceleration and the area under the curve is displacement.
Normal force (N) is perpendicular to the surface and adjusts to prevent objects from passing through it — it is not always equal to mg.
Friction (f = μN) opposes relative motion; static friction can range up to μₛN, while kinetic friction stays about μₖN.
Tension pulls equally along a massless rope and is the same throughout an ideal string over a frictionless pulley.
How to study it — and the traps to avoid
Mechanics rewards disciplined setup. Practice the same routine on every problem until it is reflexive.
Draw a free-body diagram before writing any equation.
Separate motion into independent x and y components (especially for projectiles).
On inclines, rotate axes to align with the ramp.
Check whether the system is in equilibrium (a = 0) or accelerating.
error Highest-yield trap
The normal force does not always equal mg. On an incline it is mg·cosθ, and in an accelerating elevator it changes — that is exactly why you feel heavier or lighter. Always get N from the free-body diagram, not by assuming N = mg.
Straight from the Progress Note question bank, each with a cited explanation. No account needed.
123
A community with strong social ties and shared norms experiences lower crime rates. Which sociological concept best explains this?
Answer: A. Social capital refers to the value of social networks, shared norms, and trust that support cooperation and collective efficacy. These features are associated with improved community-level outcomes, including reduced crime rates.
Source: Putnam, R. D. (2000). Bowling alone: The collapse and revival of American community. Simon & Schuster.
A newborn receives antibodies through breast milk, gaining temporary protection against infections. What type of immunity is this?
Answer: B. Passive immunity is the transfer of preformed antibodies from another source — here, maternal antibodies via breast milk (and the placenta) — which gives immediate but temporary protection because the infant's own immune system did not make them and no memory cells form. Active immunity (A, E) develops when a person's OWN immune system responds to an antigen (through infection or vaccination) and generates lasting memory, innate immunity (C) refers to nonspecific barriers, and autoimmunity (D) is an immune attack on self. Receiving ready-made antibodies is passive immunity.
Which catalytic design principle is exemplified by conformational changes that sequester reactive intermediates from solvent, as in many metabolic enzymes?
Answer: B. Flexible loops in enzymes such as triosephosphate isomerase close over the active site, stabilizing intermediates and accelerating catalysis.
What are the four kinematic equations used for?expand_more
They relate displacement, initial and final velocity, acceleration, and time for motion with constant acceleration. Each equation omits one variable, so you choose the one that leaves out the quantity you neither know nor need — for example, v² = v₀² + 2ax when time is not involved.
Why are horizontal and vertical projectile motions independent?expand_more
Gravity acts only vertically, so it changes the vertical velocity but not the horizontal one. The horizontal motion is constant-velocity while the vertical motion is free fall; the two are linked only by sharing the same time of flight.
Does the normal force always equal the weight?expand_more
No. The normal force is whatever is needed, perpendicular to the surface, to keep an object from passing through it. On a flat surface with no other vertical forces it equals mg, but on an incline it is mg·cosθ, and in an accelerating elevator it is larger or smaller than mg.
What is the difference between static and kinetic friction?expand_more
Static friction acts on a stationary object and can take any value up to a maximum of μₛN, matching the applied force until motion begins. Kinetic friction acts on a sliding object and is approximately constant at μₖN. Static friction’s maximum is usually larger than kinetic friction.
How do I find acceleration on a frictionless incline?expand_more
Resolve gravity along the ramp: the component pulling the block down the incline is mg·sinθ. Newton’s second law gives ma = mg·sinθ, so a = g·sinθ. The mass cancels, so acceleration depends only on the angle and g.