Physics

Collaboration diagram for Physics:

Topics
	2D Physics

Macros
#define	BJ_GRAVITATIONAL_CONSTANT_SI   BJ_F(6.67430e-11)

Functions
static bj_real	bj_galileo_position (bj_real position, bj_real velocity, bj_real acceleration, bj_real time)
static bj_real	bj_galileo_velocity (bj_real velocity, bj_real acceleration, bj_real time)
static bj_real	bj_newton_gravitation (bj_real m1, bj_real m2, bj_real r, bj_real g)
static bj_real	bj_newton_plummer_gravitation (bj_real m1, bj_real m2, bj_real r, bj_real g, bj_real eps)

Detailed Description

Basic physics utilities (constant-acceleration kinematics, etc.)

This header provides small helpers for common physics operations. By default, quantities are interpreted in SI units (meters, seconds), but formulas are dimensionally homogeneous: results are correct for any consistent unit system (e.g., km and s; cm and s), provided all inputs use the same system.

Dimensionality uses the base dimensions L (length) and T (time). For example:

• position: [L]
• velocity: [L T^-1]
• acceleration: [L T^-2]
• time: [T]

Macro Definition Documentation

BJ_GRAVITATIONAL_CONSTANT_SI

#define BJ_GRAVITATIONAL_CONSTANT_SI   BJ_F(6.67430e-11)

Newtonian constant of gravitation in SI units.

Defines the physical constant G = 6.67430 × 10⁻¹¹ m³·kg⁻¹·s⁻², expressed in the active bj_real precision type.

Note

Use only when working in SI units (meters, kilograms, seconds).

Function Documentation

bj_galileo_position()

bj_real bj_galileo_position ( bj_real position, bj_real velocity, bj_real acceleration, bj_real time )

inlinestatic

Galileo’s uniformly accelerated motion — position at time t.

Uses: x(t) = x0 + v0 * t + 0.5 * a * t^2

Parameters

position	Initial position [L]
velocity	Initial velocity [L T^-1]
acceleration	Constant acceleration [L T^-2]
time	Elapsed time [T]

Returns

Position at time t, in [L].

bj_galileo_velocity()

bj_real bj_galileo_velocity ( bj_real velocity, bj_real acceleration, bj_real time )

inlinestatic

Galileo’s uniformly accelerated motion — velocity at time t.

Uses: v(t) = v0 + a * t

Parameters

velocity	Initial velocity [L T^-1]
acceleration	Constant acceleration [L T^-2]
time	Elapsed time [T]

Returns

Velocity at time t, in [L T^-1].

bj_newton_gravitation()

bj_real bj_newton_gravitation ( bj_real m1, bj_real m2, bj_real r, bj_real g )

inlinestatic

Newton’s law of universal gravitation — force magnitude.

Parameters

m1	Mass of first body [M]
m2	Mass of second body [M]
r	Separation distance [L]
g	Gravitational constant G [L^3 M^-1 T^-2]

Returns

Force magnitude [M L T^-2].

bj_newton_plummer_gravitation()

bj_real bj_newton_plummer_gravitation ( bj_real m1, bj_real m2, bj_real r, bj_real g, bj_real eps )

inlinestatic

Newtonian gravitation with Plummer softening — force magnitude.

Parameters

m1	Mass of first body [M]
m2	Mass of second body [M]
r	Separation distance [L]
g	Gravitational constant G [L^3 M^-1 T^-2]
eps	Softening length ε [L]

Returns

Softened force magnitude [M L T^-2].