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
If you imagine that the block is wrung to the bottom of the water container similar to gauge blocks and there is no water between the surfaces, or any avenue for it to enter… then I don’t think there would be a buoyant force.
This is because buoyant force is a pressure difference exerted by a fluid and if there isn’t a fluid under the block it can’t exert said force from that direction. Of course in any normal situation there would be some tiny amount of water intrusion under the block and the fluid on the sides would be responsible for applying this difference in force. This is because if we imagine a column of water with a cross-section of our block going straight up compared to a similar column of pure water, if our block is less dense than an equivalent volume of water then the pure water column will have more weight and pressure. Higher pressure under the pure water column compared to lower pressure on the column with the block would result in water pushing under it, forcing the block upwards.
But in this case without any water under the block and no avenue for it to enter without the block rising from the bottom surface, I don’t see any way for there to be any water pressure under the block at all, much less the pressure difference which is the buoyant force. Of course this isn’t what the exercise is looking for so don’t put that on a test or anything.
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