weights

[colineilbeck]

if you have a rock outside a container of water and they weigh 50kg.what will the weight do if you put the rock in the water.

[newtron]

Do they have the mass of 50 kg each or together. If they are 50 kg each, the entire system (container, rock and water) will have the mass of 100 kg. If they were 50 kg together, then that would not change once the rock was put in the water. The apparent weight (not mass) of the rock in the water will be slightly less due to bouyant forces, but no mass will be lost or gained.

[ugly_bob]

terminology issue here.

The rock, technically, cannot weigh 50kg. It can have a mass of 50kg, which will not change anywhere. 50kg mass on Earth, in air, at sea level will have a weight of approx 490 Newtons, since weight is a force.

[newtron]

I believe I answered the question in a way that accounted for the terminology issue mentioned by ugly_bob.

[ugly_bob]

sorry, wasn't trying to say you hadn't newtron, just being a bit pedantic that's all.

[cyclone]

Is the container full? i.e. water spills out when you put the rock in?

The question needs some boundaries methinks.

[mibn2cweus]

Weight is a property of mass that is made apparent in the presence of gravity.

Weight is affected by the gravitational attraction present where something is weighed and the angle between the center of gravity in relation to the object and the weighing device; (the scale should be level).

Weight is also affected by buoyancy when measured in air or water. When accuracy is crucial it should be noted whether an object is weighed in air or in a vacuum when buoyancy can affect the weight measured. This can be compensated by using a balance scale with counterweights of the same buoyancy as the object being measured.

The type of weighing device could also be a consideration when weighing similar objects (or the same object) in different locations. A spring scale will indicate different weights depending on the gravitational constant for a given location. A balance scale will counteract for variations in gravity but not for buoyancy (such as changes in air pressure). For example, a balloon will weigh slightly more when inflated due to the compression of the air inside. On the other hand a deflated balloon will exhibit a slight increase in weight in a vacuum since the buoyancy of the material of which the balloon is made is no longer a consideration.

How�s that for pedantry!

So in answer to the question as I understand it; the rock will weigh less in water but will maintain its mass unless these are somehow effected by an interaction with the water such as some liberation of its composition (cleaning), or if it undergoes some type of chemical reaction.

[jenstar]

The rock will displace an equal volume of water (assuming the rock is denser than the water.)