The best replacement for projectile motion is free fall.

The best alternatives to projectile motion are rated as following:
★★★★★  free fall
★  freefall
★  inclined plane

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Speaking about projectile motion, one probably shouldn't forget about air resistance.

Other search terms related to projectile motion and their ratings are:
★★★★★ air resistance
★★ air drag
★ wind resistance
★ initial velocity
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Google Trends

Scale is based on the average worldwide traffic of projectile motion in all years. Click on graph for more.
projectile motion
free fall
freefall