Game Development Reference
In-Depth Information
Rotational Forces
A change in angular velocity of an object is caused by a force that, when applied to the object,
changes its rate of rotation around its rotation axis. This force that causes a change in the rotation
of the object is called torque. Torque can be measured as the product of the force that causes the
torque and the perpendicular distance of the force to the rotational axis. (See Figure
5-13
.)
Rotational Axis
r
Force
τ =
Force * r
Figure 5-13.
Torque
There is also an angular equivalent of Newton's second law, which is that the torque force applied
to the object is equal to the inertia of the object being rotated, times the angular acceleration of the
object. (See Figure
5-14
.)
Figure 5-14.
Torque equation
The inertia of the object depends on the shape of the object and how exactly the rotation axis is
oriented. For example, Figure
5-15
shows the rotational inertia for a hoop for a rotation axis that
goes through the center of the hoop.
R
I = MR
2
Figure 5-15.
Inertia of a hoop
