ꜱᴄɪᴇɴᴄᴇᴠᴇʀꜱᴇ🚀 on Instagram: "Inertia (Newton's First Law) means an object keeps moving at the same speed and direction unless a force acts on it. So, here, the ball initially wants to keep moving forward with the car's speed. But then, the ball is thrown backward at the same speed as the car's forward motion so the speeds cancel out (relative to the ground). 40km/h- 40km/h = 0 km/h Now, this canceling of speeds happens because you give the ball a backward velocity equal to the car's forward vel