The source of my question can be found via this link:
https://www.youtube.com/watch?v=wwjtuZ5vTvc&index=94&list=PLAD5B880806EBE0A4
There is an object that weight 10N outside of water and 2N inside water. I want to understand the buoyant force acting on it using a free body diagram.
As per the above video, it says that the buoyant force is 8N = 10N – 2N and the free body is drawn as follows
Weight of object 10N downwards and 8N upward buoyant force which gives a net force of 2N. I am confused because if there is a remaining net force of 2N then shouldn't the object be sinking? for it to submerge and not sink the upward force must cancel out the downward force, correct? Can some explain me the forces acting on this object under water? and how to use the weight inside water and outside water to determine buoyant force?
Best Answer
Yes, you are very correct in saying that if there is a non-zero net force, then the object will accelerate.
No. You must have missed that the object is held up by a scale or a string. The same is the case in the water. Without the string to hold it up, it would sink, because - as you rightfully say - the net force is downwards. But the string gives the remaining force to balance it all.