The science standards that are specifically addressed through this lesson are: 8.1 Motion and 8.2 Forces.

1. The velocity of an object is the rate of change of its position. As a
basis for understanding this concept, students know: 

a. position is defined relative to some choice of standard reference point and a set of reference directions. 

b. average speed is the total distance traveled divided by the total time elapsed. The speed of an object along the path traveled can vary. 

c. how to solve problems involving distance, time, and average speed. 

d. to describe the velocity of an object one must specify both direction and speed. 

e. changes in velocity can be changes in speed, direction, or both. 

f. how to interpret graphs of position versus time and speed versus time for motion in a single direction. 


2. Unbalanced forces cause changes in velocity. As a basis for understanding this concept, students know: 

a. a force has both direction and magnitude. 

b. when an object is subject to two or more forces at once, the effect is the cumulative effect of all the forces. 

c. when the forces on an object are balanced, the motion of the object does not change. 

d. how to identify separately two or more forces acting on a single static object, including gravity, elastic forces due to tension or compression in matter, and friction. 

e. when the forces on an object are unbalanced the object will change its motion (that is, it will speed up, slow down, or change direction). 

f. the greater the mass of an object the more force is needed to achieve the same change in motion. 

g. the role of gravity in forming and maintaining planets, stars and the solar system.

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