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Newton's second law

Newton's second law says that the sum of the forces on a body equals the mass times the acceleration. Force and acceleration point the same way. If the sum is zero, the acceleration is zero and the velocity is constant. That is the content of the first law. Mass is in kilograms and force in newtons. Draw the forces first, find the sum along the motion, and divide by the mass.

\sum F = ma

Newton's second law

Symbols

$\sum F$	sum of the forces	N
$m$	mass	kg
$a$	acceleration	m/s²

Example

The sum of the forces on a box is 40 N, and the mass is 8 kg.

$a = 40/8 = 5$ m/s² in the direction of the force.

Forces that act against the motion are entered with a negative sign when the positive direction is the direction of motion.

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Part of Physics 1: Forces and Newton's laws.