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Suppose there is a weighing balance.In one hand of weighing balance there is weight of 1 KG which is perfectly balancing flask full of water which is on the other hand. Now if i immerse finger in water, will the equillibrium be disturbed?
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Stercus- Member Since Dec-2007 | Aug 18th, 2009
Akash, your FBD won’t work if you leave off external contacts – they need to be converted to force arrows. The buoyed object provides one such force: the buoyant reaction force.
You seem to agree that there is a force acting upwards on the test tube, appearing on the spring balance acting against the weight. As the test tube and the bowl of water are stationary, not accelerating, there must be an equivalent reaction force acting downwards on the body of water, imparted by the object. To go into more detail, the surface of the object experiences a pressure distribution from the water, gradated downwards due to increasing pressure within the water body. The net result from the pressure distribution is that the water pushes up on the object (buoyant force). To avoid being crushed, the object pushes back against this pressure in all directions – so again you get net a reaction force in the opposite direction, downwards.
So the FBD of the water body needs a reaction force to account for buoyancy. This reaction force acts downwards, from the centre of the displaced volume and is equal to the weight of the water displaced. The weight of the object immersed doesn’t need to be considered as this is supported but the weight of the displaced volume of water does.PRASHANT
- Oct 16th, 2011
It will not change the reading..... Lets take a simple case... A water flask is putted on a weight balance and a rod is immersed in it which is tied to ceiling with help of a rope. The tension in the...
