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176 RIGID BODIES
DYNAMICS
DYNAMICS
RIGID BODIES 177
The spring pulls both spheres
with the same force giving a
higher acceleration to the right
sphere, making it oscillate more.
In the diagram above, two spherical rigid bodies are attached via a spring. Note how
the smaller mass is oscillating over a greater distance. This is because the left sphere
has a large mass, which in turn needs a higher force to give it the same acceleration.
The spring pulls both spheres with the same force giving a higher acceleration to the
right sphere, making it oscillate more.
Two cases of a black sphere
shooting into a white sphere
that is initially at rest.
Above you can see two cases of a black sphere shooting into a white sphere that is
initially at rest. In the rst case, the white sphere has a smaller mass than the incoming
black sphere and hence it is moving rapidly after the collision. In the second case,
however, the white sphere has a larger mass and so the black sphere makes little
impact on the sphere during the collision making it move slowly after the collision.
To summarize these two diagrams:
Forces being equal, a small mass will be accelerated more and tend to move faster
than a larger mass.
The greater the mass, the greater the force required to achieve the same
acceleration.
When two objects of different mass collide, the smaller mass will be affected most.
If, on the other hand, you set the Total Mass to 0, the following will apply:
The dynamics engine will exert no force on the rigid body.
You will be able to animate the rigid body using keyframes in the Timeline, even if
the rigid body is attached to another rigid body via a spring.