Physics Classroom
The Physics Classroom: Newton's First Law of Motion
A clear explanation of Newton's First Law of Motion, the law of inertia, with diagrams and real-world examples. Useful for both students and teachers. Written by a high school physics teacher.
Khan Academy
Khan Academy: Applying Gravity to a Particle
Next, let's apply all these ideas to the case where a particle is being acted on by both gravity and air resistance using this 5-question quiz/practice. The gravity force vector points downward, and the air resistance force opposes it.