Motion
1. The velocity of an object is the rate of change of its position. As a basis
for under-standing this concept:
a. Students know position is defined in relation to some choice of a standard
reference point and a set of reference directions.
b. Students know that average speed is the total distance traveled divided by
the total time elapsed and that the speed of an object along the path traveled
can vary.
c. Students know how to solve problems involving distance, time, and average
speed.
d. Students know the velocity of an object must be described by specifying
both the direction and the speed of the object.
e. Students know changes in velocity may be due to changes in speed,
direction, or both.
f. Students know how to interpret graphs of position versus time and graphs of
speed versus time for motion in a single direction.
Forces
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.
