Fuerza Normal
Calcula la fuerza normal N = mg o N = mg cos θ en rampas. Incluye casos con fuerzas aplicadas verticales.
Fórmula principal
N = mg or N = mgcos(theta)
How do you calculate normal force?
On a horizontal surface with no other vertical forces, N = mg. On an incline with no extra perpendicular forces, N = mg cosθ. If something pushes down on a floor, N = mg + F_down; if something lifts, N = mg − F_up (and N cannot go below zero while contact lasts).
Sobre esta herramienta
La fuerza normal equilibra componentes perpendiculares al contacto (N = mg en horizontal, N = mg cos θ en planos inclinados). Ideal para diagramas de cuerpo libre introductorios.
Cómo usar esta calculadora
- Elige la variable que quieres despejar y confirma qué valores ya conoces.
- Introduce los datos en unidades coherentes antes de calcular.
- Comprueba si el resultado es físicamente razonable comparándolo con las entradas.
- Usa el desglose paso a paso para ver cómo se aplicó la fórmula.
Ejemplos resueltos
Example 1: 5.0 kg on a flat floor
With g = 9.8 m/s² and no extra vertical force, N = mg = (5.0)(9.8) = 49 N upward. The floor pushes up with 49 N; the block pushes down on the floor with 49 N.
Example 2: same mass on a 30° ramp
N = mg cosθ = (5.0)(9.8) cos(30°) = 49 × 0.866 ≈ 42.4 N. Check: at 0° this would be 49 N; at 60° it would be 24.5 N.
Example 3: 20 N downward push on a floor
A 2.0 kg box sits on a table while you push down with 20 N. N = mg + 20 = 19.6 + 20 = 39.6 N. A 20 N upward lift would give N = 19.6 − 20, which is not possible while contact remains — the box would leave the table.
Preguntas frecuentes
What is the formula for normal force?
The default school cases are N = mg on a horizontal surface and N = mg cosθ on an incline, with θ measured from the horizontal. Extra perpendicular forces add or subtract from that support.
Is normal force always equal to weight?
No. N equals weight only on a flat surface with no other vertical forces. On a ramp, in an elevator, or when you push down on a box, N is different from mg.
Why is it mg cosθ on an incline?
Weight still points straight down. The surface can only push perpendicular to itself, so the component of mg into the ramp is mg cosθ. The remaining mg sinθ is parallel to the ramp.
How does normal force relate to friction?
Kinetic or maximum static friction is Ff = μN. If you use mg instead of mg cosθ on a ramp, both N and friction will be wrong.
Can normal force be zero?
Yes, at the instant contact is lost — a jump off the floor, or an upward force larger than weight. While the object stays in contact, N ≥ 0.