A 5 kg box has a 30 N push force and 10 N friction. What is the acceleration?

Net F = 30 - 10 = 20 N. a = F/m = 20/5 = 4 m/s².

Why doesn't a book sitting on a table fall? What forces act on it?

Two forces: gravity pulls it down (W=mg), the table pushes it up (normal force N). These are balanced (N=W), so net force = 0, acceleration = 0 — the book stays at rest (Law 1).

Why does a car accelerate more slowly when fully loaded vs empty?

F=ma → a=F/m. With more mass (loaded car), the same engine force (F) produces smaller acceleration. To get the same acceleration with more mass, you need more force.

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Newton's Laws on an Incline

Inertia, net force, friction, and F=ma

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How it works

Newton's First Law describes motion when the net force is zero: an object stays at rest or continues at constant velocity. Newton's Second Law connects the net force to acceleration through F=ma. On an incline, gravity contributes a component parallel to the ramp while friction opposes the direction of motion. Changing the ramp angle, mass, applied force, or friction changes the net force and therefore the acceleration.

Step-by-step

Choose a preset or adjust the ramp angle, applied force, object mass, and friction coefficient.
Compare the force arrows with the net-force and acceleration readouts.
Set the ramp angle and applied force to zero to inspect a balanced-force case, then introduce a net force to test F=ma.

Key formulas

$\text{1st: } \sum F=0 \Rightarrow a=0 \quad \text{(inertia)}$ Law 1: An object at rest/motion stays that way unless acted on by net force
$\text{2nd: } \sum F = ma \quad a = \frac{F_{net}}{m}$ Law 2: Net force equals mass times acceleration

Frequently asked questions

A 5 kg box has a 30 N push force and 10 N friction. What is the acceleration?: Net F = 30 - 10 = 20 N. a = F/m = 20/5 = 4 m/s².
Why doesn't a book sitting on a table fall? What forces act on it?: Two forces: gravity pulls it down (W=mg), the table pushes it up (normal force N). These are balanced (N=W), so net force = 0, acceleration = 0 — the book stays at rest (Law 1).
Why does a car accelerate more slowly when fully loaded vs empty?: F=ma → a=F/m. With more mass (loaded car), the same engine force (F) produces smaller acceleration. To get the same acceleration with more mass, you need more force.