Newton's Laws of Motion in Physics

A force is not something a body carries around, it is an interaction, and it only shows itself in what the body does next. The three laws on this page say what that interaction changes and what it can never change. The first fixes the case of no net force, where the velocity is stuck. The second ties net force to mass and acceleration. The third says every push is repaid in full. The blocks then work through where the forces actually come from, weight, the normal reaction, tension and friction, so that a free-body diagram can be written straight into an equation.

Net force on a body at rest or moving at constant velocity

Given

Equilibrium split into components

Given

Net force from the mass and the acceleration

Given

(kg)
(m/s²)

Acceleration from the net force

Given

(N)
(kg)

Mass from the net force and the acceleration

Given

(N)
(m/s²)

Newton's second law split into components

Given

(kg)
(m/s²)

Weight of a body near the Earth

Given

(kg)

Constant used

Gravitational force between two masses

Given

(kg)
(m)

Constant used

Field strength at a distance from a planet

Given

(kg)
(m)

Constant used

Apparent weight when a lift accelerates upward

Given

(kg)
(m/s²)

Constant used

Apparent weight when a lift accelerates downward

Given

(kg)
(m/s²)

Constant used

Force of one body on another and the force back

Given

Normal reaction on a horizontal surface

Given

(kg)

Constant used

Normal reaction when a force pulls upward at an angle

Given

(kg)
(N)
(rad)

Constant used

Normal reaction when a force pushes downward at an angle

Given

(kg)
(N)
(rad)

Constant used

Acceleration on a frictionless level surface with a force at an angle

Given

(N)
(rad)
(kg)

Normal reaction on an incline

Given

(kg)
(rad)

Constant used

Acceleration down a frictionless incline

Given

(rad)

Constant used

Acceleration down a rough incline

Given

(rad)

Constant used

Acceleration of two masses joined over a pulley

Given

(kg)
(kg)

Constant used

Tension in the string joining two masses over a pulley

Given

(kg)
(kg)

Constant used

Acceleration of two joined bodies pulled along a level surface

Given

(N)
(kg)

Greatest static friction before sliding begins

Given

Kinetic friction while a body slides

Given

Smallest horizontal force that starts a body sliding

Given

(kg)

Constant used

Angle of an incline at which a body just begins to slide

Given