eloquent logic - dynamics

Legend

F_net	=	net force
m	=	mass
a	=	acceleration
F_g	=	force of gravity

Net Force

A net external force (due to unbalanced forces) acting on an object affects the object's speed and/or direction; it causes an acceleration directly proportional to the amount of force applied and in the direction of that force. This law of acceleration has the equation of F_net = ma.

Example:

Person exerting a horizontal force on a fridge causing it to accelerate sideways

If the only horizontal force acting on a body of mass m is F, then it will accelerate horizontally such that F = ma. This motion is independent of the vertical forces that we'll deal with shortly.

This is a free-body diagram showing the net horizontal force. It allows us to see all the forces add up and determine the net result.

A person on the left and a person on the right of the fridge exert equal opposite forces which cancel meaning the fridge will not accelerate

Two people apply equal, oppositely directed forces to an object. Because force is a vector quantity, these two forces cancel each other and "horizontal" F_net = 0, which means there cannot be any horizontal acceleration.

The free-body diagram shows the blue arrows pushing it up as a reaction force due to gravity.

Dynamics Intro

Vector Dynamics