Jenga Kebab! The Magic of Static FrictionRaj GadgeAward: Top 100
School: john p. stevens high school My uncle's family had recently visited us for spring break, which was exciting since they had a 4 year old toddler who I loved spending time with. At some point I attempted to teach my cousin how to play Jenga, which to nobody's surprise ended up wildly unsuccessful. Despite this, I noticed something interesting: toddlers seemed to have a strange affinity for Jenga blocks, beyond just trying to eat them. Seeing how enamored she was, I decided to blow her little mind with a "magic trick, " where I lifted a bunch of blocks in front of her without actually touching the blocks themselves. How, you ask? With what I call a Jenga Kebab! The trick works by sandwiching a group of blocks (the "kebab") between two end blocks and then pushing on the ends. This creates an equilibrium of forces that prevents the system from moving. Internal forces between the kebab blocks within the system cancel out, so only the external forces matter. Horizontally it's balanced because the end blocks push on the system in equal magnitudes and opposite directions; and vertically it's balanced as the forces of gravity and friction are also equal and opposite. This is because the force of the end blocks provides the normal force that creates static friction. But, if the frictional force was weaker than the weight, that would cause the system to slip, meaning you need to push harder when there are more blocks because the weight of the system is bigger. 
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