Why are things lighter(as in weigh less) in water?

Answer 1

Things seem lighter because of buoyancy.

Buoyancy works because to push something into a fluid, you have to displace some of the fluid to do it. The fluid wants to get back in, so it's essentially trying to force the object out again. The amount of force this applies depends on the volume of the object, and the density of the fluid.

For example, if you push a two-liter bottle under water, there's two liters of water you're going to be pushing out of the way. Those two liters of water typically weigh about two kilograms, or roughly five pounds, so you'll feel five pounds of pressure pushing back up. OR whatever's in the bottle seems to weigh five pounds less...

This also explains why boats can float (their weight is much less than the water they displace) and how changing the volume of something can make it float or sink (like if you hold a lot of air in your lungs instead of making them empty).

This works in the atmosphere too. By walking around on the ground, you're displacing some air that wants to be where you are. Air is a lot less dense than water, but it still provides you with a little buoyancy, if only a few grams' worth. But this also explains how helium and hot-air balloon float, for example.

How that helps!

Answer 2

Weight is the magnitude of the normal force a scale exerts on an object when the object is stationary relative to the scale.

Buoyancy force acts opposite the gravitational force reducing the net acceleration on the object and consequently the normal force needed to be exerted by the scale to keep it from accelerating falls.

Buoyancy originates by displacing a volume of water equivalent to the volume of the submerged object. This object actually feels the pressure gradient of the water; the pressure is higher on the bottom surface of the object than it is on the top surface of the object resulting in a net upwards force.

Definition of Weight

Submerged objects do in fact weigh less. Weight is the net gravitational plus buoyant force times the mass of the object. While the mass does not change in water, the measured weight does. Put a scale in the water and place an object on it. The object will weigh less, even though it still masses the same.

An object in free fall with a scale has 0 weight, but it still masses the same. What is the weight of a 1kg block of lead in the microgravity of the space shuttle? It still masses 1kg but it weighs less.

Answer 3

The pressure gradient in the water exerts an upward force, called buoyancy, that counteracts the force of gravity. The object's weight doesn't actually change, as you can tell if you weigh the object and the water together.

But if you weigh an object in water, part or all of it's weight is canceled by buoyancy, so you will get a lower number. If the object's density is less than water's it will float, and if you weigh it under water its "weight" will be negative.

Answer 4

Well, think of gravity as a vector pulling down on an object. The magnitude of the vector would be the weight. When you put an object underwater, the water's buoyancy creates an upward 'lift,' or an upward vector. The upward vector cancels out some of the downward vector, and therefore decreases the magnitude ( weight ) of the downward vector ( gravity )

Answer 5

they weigh the same, unless I'm confused by the question.

Weight is simply the force you exert determined by the strength of gravity. Eg, your weight on the moon is would be much less than that say on Jupiter - simply because gravity is stronger on Jupiter.

Maybe you're talking about buoyancy - which is something very different

Answer 6

Buoyancy. When you are in water your body dispaces water equal to the volume of your body that is submerged. In order to do this the water that would have occupied this space must be pushed away; the perceived weight loss is due to push back that the water exerts on the body.

Answer 7

Things are not lighter or heavier, buoyancy is dependent on molecular structure, none-the-less, its mass remains the same in water.

Answer 8

Things don't weigh less in water, they just move slower. Water is denser than air, so it takes more time for something to move through it, than air.

Answer 9

there is less gravity in water. just like in space.
should've listened in class today.

Answer 10

i think cause you have a pressure from the water