EarthSurfaceGravAccel
Near Earth's surface, the magnitude of the gravitational acceleration, $g$, is approximately $9.8 \, \mathrm{m/s}^2$.
EarthSurfaceGravDir
Over a sufficiently small area of Earth's surface, the direction of Earth's gravitational acceleration can be approximated as constant, and defines "down".
KinEqn2_dvt
One-dimensional motion with constant acceleration is described by the equation $x_\text{2}=x_\text{1} + \frac{1}{2} (v_\text{1}+v_\text{2}) (t_\text{2}-t_\text{1})$, where $x_\text{2}$ is the position at time $t_\text{2}$, $x_\text{1}$ is the position at time $t_\text{1}$, $v_\text{2}$ is the velocity at time $t_\text{2}$, and $v_\text{1}$ is the velocity at time $t_\text{1}$.
KinEqn3_dv_plus_at^2
One-dimensional motion with constant acceleration is described by the equation $x_2=x_1 + v_1 (t_2-t_1)+\frac{1}{2} a (t_2-t_1)^2$, where $x_2$ is the position at time $t_2$, $x_1$ is the position at time $t_1$, $v_1$ is the velocity at time $t_1$, and $a$ is the acceleration.
TopOfFlight
At the highest point of an object's trajectory, the vertical component of the object's velocity is zero.
