Hey guys, so my question basically boils down to, in the linked image below, **why is buoyant force exerted by the fluid** ***surrounding*** **the block instead of just the fluid** ***underneath*** **the block**, when buoyant force direction is straight upwards only? Like what property of the fluid molecules on the sides and top of the block is causing them to pull the block upwards?
Or in other words, there’s no water below the block, so what is pushing it upwards apart from the normal force? Thanks.
[https://prnt.sc/r9oh1o](https://prnt.sc/r9oh1o)
In: Physics
Think of the water being divided into really thin horizontal strips.
The topmost strip of water is just kinda… there. It wants to spread out across its container. And if the block encounters it, the water will squeeze the block a little bit as it wants to spread.
The next strip below does the same thing, except now it has the top strip of water on top of it, weighing down on it. The weight of the water above makes it squeeze on the block just a little bit harder.
Each subsequent strip down increases this squeezing effect due to the weight of water above it. This is why water pressure increases only as a function of depth, no matter how much water you actually have. A big, deep pool will have the exact same pressure at the bottom as a tall, narrow column of the same height.
Buoyancy arises (ha) because when you put any 3D object into water (or any fluid, for that matter) the part of the object that is deepest submerged is being squeezed slightly harder than it is at the top. A higher pressure at the bottom an a lower pressure at the top results in a net force that causes the object to feel an upward force. If that force is greater than the object’s weight, it will float upwards until this buoyant effect balances its weight force exactly.
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