# Physics

There are some basic principles governing the motion of objects, some of which are scientifically valid and some of which are merely observations or conjectures of EDGE members.

## Translational Kinetic Energy

The kinetic energy contained in a moving disc is the combination of  its linear kinetic energy and its rotational kinetic energy:

For all practical purposes, the mass (m) and the rotational inertia (I) for a disc is constant for each and every disc.  If the mass of the disc is increased, it takes a greater linear velocity and angular velocity to maintain a given translational kinetic energy.

## Moment of Inertia

The moment of inertia is a rotating object's resistance to rotational acceleration.  For a given torque, the greater the moment of inertia of a body, the less its angular acceleration.

## Gyroscopic Stability

Gyroscopic stability is the tendency of the spin axis of a rotating body to remain in a fixed orientation.  A rapidly spinning disc will have a tendency to maintain the x-y-z orientation it has when released from the hand.  As long as the disc is spinning rapidly, it will maintain its orientation.  As soon as the disc begins slowing down (both its linear and rotational velocities), other forces begin to take over.

## Precession

Precession is motion that results from the application of a torque that tends to displace the action of a rotating object.  The property of Precession represents a natural movement for rotating bodies, where the rotating body doesn’t have a confined axis in any plane. Toy "tops" are good examples of precessing objects. See the diagram below for no reason other than this page looks a lot better with some color added to it and it has the word "precession" in it...

## Air Resistance

The slimmer the profile of a disc, the less air resistance it encounters. The more dense the air, the greater the air resistance.  All other things being equal, the greater the velocity of the disc, the greater the air resistance upon it.

NOTE: It has been scientifically verified by members of the EDGE that there is are such things as "good air" and "bad air".

## Bernoulli Effect

All discs are essentially airfoils, much like airplane wings.  In order for an airfoil to generate lift, the upper surface must be shaped in such a way that when air passes over it, a region of low pressure must be created.  At least, the pressure above the disc must be lower than the pressure below it.  It's the difference in air pressures that keeps the disc in the air.  Ultimately, gravity will have its way.

## Coefficient of Suckage

The coefficient of suckage is a constant that has a direct impact on disc golf performance. The amount of suckage a player tends to exude is directly proportional to his/her frame of mind and increases exponentially with the desire to reduce the coefficient of suckage during any given round of disc golf.

One of the fundamental equations in all of disc golf physics is shown above.

Because the coefficient of suckage is a constant, all attempts to reduce it merely increase the amount of actual suckage in the system.

Basic Physics

Mass is defined as an  object's resistance to change in motion.

Velocity is the rate of change of displacement of an object.

The momentum of an object is a product of its mass and its velocity.

The acceleration of an object is directly proportional to the force imparted to it and inversely proportional to the mass of the object.

The angular acceleration of an object is directory proportional to the torque imparted to it and inversely proporational to the rotational inertia of the object.

The resistance encountered by a body moving through a fluid (such as air) is proportional to the product of the cross-sectional area of the object (A) and the square of the velocity (v).  The constant (C) is basedon the object's shape and the fluid's density.