Newton's Laws of Motion

First law: inertia. Second law: F = ma. Third law: action and reaction are equal and opposite. These laws form the foundation of classical mechanics.

First law (law of inertia)

An object remains at rest or in uniform motion in a straight line unless acted upon by a net external force. In other words, if the net force is zero, the acceleration is zero. This law defines inertia: the tendency of an object to resist changes in its state of motion.

Second law

The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass: F = ma, or a = F/m. So a larger force gives greater acceleration; a larger mass gives smaller acceleration for the same force. The second law allows us to predict motion when forces are known.

Third law (action–reaction)

When one body exerts a force on a second body, the second body exerts an equal and opposite force on the first. These forces act on different bodies, so they do not cancel each other. For example, when you push a wall, the wall pushes you back with the same magnitude of force.

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