Motion and Collision - Beginning Android 3D Game Development - page 136

Figure 5-3. Instantaneous velocity definition
The average acceleration of an object is the change in velocity divided by the change in time.
(See Figure 5-4 .)
Figure 5-4. Average acceleration definition
The instantaneous acceleration is the change in velocity divided by the change in time as the time
interval goes to 0. (See Figure 5-5 .)
Figure 5-5. Instantaneous acceleration definition
Newton's Laws of Motion
In order for an object to change its velocity, an external force must be applied to that object.
Newton's laws of motion are used to describe this force in terms of the object's mass and
acceleration. There are three laws of motion, and they are described as follows:
Newton's first law: Consider a body on which no net force acts. If the body is
at rest, it will remain at rest. If the body is moving with a constant velocity, it will
continue to do so.
Newton's second law: The sum of the external forces acting on an object are equal
to that object's mass, multiplied by its acceleration. Figure 5-6 shows the vector
form of this law. Figure 5-7 shows the scalar version of this law, with forces grouped
along the x, y, and z axes.
Figure 5-6. Newton's second law vector equation