Game Development Reference
In-Depth Information
The presence of wind changes the apparent velocity seen by a projectile. In Figure 5-10, a
projectile travels with a velocity,
v
. There is a wind present with a velocity,
v
w
. The apparent
velocity,
v
a
, seen by the projectile is the vector sum of the projectile and wind velocities. The
directional components of apparent velocity are found by subtracting the wind velocity compo-
nents from the translational velocity components.
v
=−
v
v
(5.23a)
ax
x
wx
v
=−
v
v
(5.23b)
ay
y
wy
v
=−
v
v
(5.23c)
az
z
wz
Figure 5-10.
Apparent velocity is the vector sum of the projectile velocity and wind velocity.
The wind velocities are subtracted from the projectile velocities in Equation (5.23) because
a positive wind velocity in the x- or y-direction will decrease the apparent velocity in the x- or
y-direction.
The presence of wind alters the aerodynamic drag experienced by the projectile. In the
presence of wind, the total drag force and directional drag force components are computed
using the apparent velocities experienced by the projectile.
1
---
rAC
D
v
2
F
D
=
(5.24)
v
F
=−
F
xa
(5.25a)
Dx
D
v
a
v
ya
F
=−
F
(5.25b)
Dy
D
v
a
v
F
=−
F
za
(5.25c)
Dz
D
v
a
v
=++
v
2
v
2
v
2
(5.26)
a
xa
ya
za
The equations of motion when wind effects are included are solved in exactly the same
way as when only drag was included. The only difference is that the apparent velocity is used to
compute the drag force. The acceleration components would be equal to the force components
