NSES Content Standard B 
Physical Science: Motions and forces
Grades 5-8, page 154

An object that is not being subjected to a force will continue to move at a constant speed and in a straight line.

Benchmark 4F The Physical Setting: Motion
Grades 6-8, page 90
An unbalanced force acting on an object changes its speed or path of motion, or both. If the force acts toward a single center, the object's path may curve into an orbit around the center.