California State Science Standards Grade 8 - Forces
Standard 2: Unbalanced forces cause changes in velocity.
2b: Students know when an object is subject to two or more forces at once, the result is the cumulative effect of all the forces.
2c: Students know when the forces on an object are balanced, the motion of the object does not change.
2d: Students know how to identify separately the two or more forces that are acting on a single static object, including gravity, elastic forces due to tension or compression in matter, and friction.
2e: Students know that when the forces on an object are unbalanced, the object will change its velocity (that is, it will speed up, slow down, or change direction).
2f: Students know the greater the mass of an object, the more force is needed to achieve the same rate of change in motion.