# Terminology

Cool words but i have no idea what they all mean

Terminology

Acceleration (a) - meter per second squared (m/s^2).

The rate at which the velocity of a body change over time.

Buoyancy

Upward force exerted by a fluid of an immersed object. The magnitude of that force is the same as the weight of the displaced fluid.

Center of mass

The center of mass is the balance point of the body where all the mass even out on all sides.

Constraint

A constraint connect two rigid bodies and apply limits on how they can move or what forces can affect them.

Damping

Linear and angular dampening can be used on a body. It will slow down the movement of the body so it comes to a halt if no other forces keep acting on it.

Density (p)

How much mass a substance has per unit volume (p = m / V). The SI-unit is kg/m^3. Water have a density of 1000.

Force (F) - newtons (N)

Friction

When surfaces in objects slide against each other a force is created between the two surfaces. Static friction and kinetic friction.

Inertia

A objects resistance to a change in rotation.

Integrator

k-DOP

A k-DOP is a bounding volume that is created by taking k planes around the object at infinity and pushing them in until the touch the object. Common k values are 6, 10, 18 and 26. The final number of faces on the bounding box can be less then k as a edge or a vertex can become degenerate.

Kinematic body

Not moved by physics, it is updated by the game. But it can make other things move.

Mass (m) - kilogram (kg)

A physical body's resistance to being accelerated by a force.

Meter - meter (m)

Unit of length

Ragdoll

This is a group of rigid body's that are constrained to each other.

Restitution

A normalized value that describe how bouncy a body is. If 0.75 the body will keep 75% of its speed after the collision

Rigid Body

A physic object that can be any form but the the parts always stay in the same position relative to each other.

Shape

For speed the simplest possible geometric primitives should be used to describe the form of a body. A lamp post can use a box as a bounding volume to make it more easy for the collision system to handle. For better detail one can use more then one shape so a table can be one box for the surface and then one box for each leg. Shapes for 2D is circle, rectangles and polygons. Common in 3d are boxes, capsules, cylinder, spheres or k-DOP's.

Sleeping

Body's that does not move or are affected by any force are put to sleep so they do not need to be updated by the physics system. They will wake up again if they collide with any body that is awake or is given a force.

Static Body

A static body never moves so it needs no mass.

Time (s) - seconds (s)

Timestep

The physics world is updated by stepping it forward in time. By always using the same stepsize it make the physics more predictable.

Velocity - meters per second (m/s)

How fast the position of a body change. It's a vector with both a magnitude and a direction. The magnitude is called speed.

Reference