2.Unbalanced forces cause changes in velocity. As a basis for understanding this concept:
- a. Students know a force has both direction and magnitude.
- b. Students know when an object is subject to two or more forces at once, the result is the cumulative effect of all the forces.
- c. Students know when the forces on an object are balanced, the motion of the object does not change.
- d. 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.
- e. 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).
- f. Students know the greater the mass of an object, the more force is needed to achieve the same rate of change in motion.
- g. Students know the role of gravity in forming and maintaining the shapes of planets, stars, and the solar system.