Newton's third law of motion states: "An object that is at rest
will remain at rest, or an object that is moving will continue to
move in a straight line with constant velocity, if and only if the
net force acting on the object is zero" (Knight 128). Ballroom
dancing is an excellent demonstration of inertia.
When a couple join and create a frame for dancing they are not
yet in motion, they are at rest. The dance does not start when the
music starts, the dance starts when the Lead creates a net force
greater than zero. Without this initial force the couple does not
dance.
Once dancing, the couple continues moving in a straight line with a constant velocity (directly related to the tempo of the music) until the Lead creates another force. Follows are taught to take no action and make no changes in their movements until lead. Admittedly, some exceptions are made for the presence of walls, abrupt drop offs, and other dancing couples but the rule for inertia still applies. The couple will not change course until a net force greater than zero is applied.
Even in spins and turns the rule is upheld. To initiate a turn or
spin the lead applies a new force and then maintains it until the
completion of the movement. The net force returns to zero and the
couple continues in a straight line at a constant velocity.
 Glossary of Terms |
Spins |
Turns |
Frame |