Newton's Third Law meets Platform Nine and Three Quarters

(end 0:08) We are all familiar with the “Platform Nine and Three Quarters” scene from Harry Potter and the Sorcerer’s Stone. Now, lets analyze the physics behind it… When Harry first tries to enter the platform, he hits the brick wall with his cart head on. Which do you think experienced the greater force during the collision; Harry’s cart, or the brick wall? Many people would assume that the brick wall would have more force since it has more mass. However, this is not the case… Newton’s Third Law states that every action has an equal and opposite reaction. That being said, the cart and the platform actually exert equal forces on each other. Which object experiences a greater acceleration? Think back to Newton’s second law… The force is the same, and mass and acceleration are inversely proportional. This means that since the mass of the platform is greater than that of the cart, the acceleration will be smaller. And similarly, since the mass of the cart is smaller, it’s acceleration will be greater. It’s magical, isn’t it?