what's going on?
This trick reminds me of that motorbike stunt inside a huge spherical cage. When the riders get up enough speed they can ride around sideways or even upside down. The force that keeps these daredevils and your marble stuck to the glass is called the centripetal force and it results from the marble's circular path and the shape of the glass. You experience the centripetal force pushing you 'sideways' inside a car every time you go around a corner. Inside a car, the physics is very intuitive: the faster you go or the sharper the corner, the greater the 'sideways' force. And you'd rather be sitting next to a little sister than a big uncle because the heavier an object, the greater the sideways force. The reason you experience this force is because any object in motion tends to stay in motion in a straight line unless something gets in the way. Once moving, the marble wants to keep moving in a straight line but the curved walls of the glass make it change direction. As a result, the marble pushes against the glass. From the marble's perspective, your upside down glass has walls which bank up and outward, so it rises up. As long as you keep the marble racing, it keeps climbing the glass and stays put.
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