What the ASVAB is testing
Force questions test whether you can apply Newton's laws and pressure formulas to real scenarios: a vehicle accelerating, a piston in a hydraulic system, a box being pushed across a floor. The math is straightforward — the trap is picking the wrong formula or forgetting about direction.
Newton's laws in plain terms
First law (inertia): An object keeps doing what it's doing — moving or stationary — until a net force acts on it. This is why a vehicle skids when brakes lock: the wheels stop turning, but the car's inertia keeps it moving forward.
Second law: F = ma. Force equals mass times acceleration. If you double the force on the same mass, you double the acceleration. If you double the mass with the same force, you halve the acceleration. This is the workhorse formula for MC force problems.
Third law: Every action has an equal and opposite reaction. When a rifle fires, the bullet goes forward and the gun recoils backward. When a rocket engine pushes exhaust down, the rocket goes up.
Friction
Friction always opposes the direction of motion. Two types matter here:
Static friction keeps an object from moving when a force is applied. It matches the applied force up to a maximum (μs × N). Once that maximum is exceeded, the object starts moving.
Kinetic friction acts while the object is in motion and is lower than static friction. This is why it's easier to keep a box sliding than to get it started.
The normal force N is perpendicular to the surface — on a flat floor it equals the object's weight. On an incline, it's reduced by the angle.
Pressure and Pascal's law
Pressure = Force ÷ Area. Concentrate the same force over a smaller area and pressure goes up (sharp knife cuts better than a dull one). Spread it over a larger area and pressure drops (snowshoes prevent sinking).
Pascal's law: pressure applied to an enclosed fluid is transmitted equally in all directions. This is the basis of hydraulic systems. A small piston with high pressure can drive a large piston with large force.
Net force
When multiple forces act on an object, find the net force before applying F = ma. Forces in the same direction add; forces in opposite directions subtract. If a 50 N push meets 20 N of friction, the net force is 30 N — not 70 N.