I learn that inertia means the tendency an object will remain from changes. Heavier object has higher inertia, which means higher tendency to resist change. So, here is an example from my teacher. A car accelerates, the driver is pulled backward and hit the rear of his seat. This is due to inertia of the driver-- he tends to remain in rest rather than accelerating. My problem is, the car is definitely heavier than the driver, which means the car should have higher inertia than the driver. Why the car moves, but the driver tends to remain in rest?