Video narration
Why do you lean forward when a bus suddenly brakes? The bus isn't pushing you forward. It slows; your body keeps moving. That resistance to a change in motion is inertia: Newton's First Law. The Second Law connects net force to acceleration: for constant mass, F = ma. The Third Law is action-reaction: equal, opposite forces act on different bodies. So when the bus stops, your body tends to keep moving forward-that's inertia, explained by the First Law.