# How to calculate bouyant forces of objects submerged in water

To find the force of buoyancy acting on the object when in air, using this particular information, this formula applies: Air's density is very small compared to most solids and liquids. Fluid Dynamics Video transcript Let's say that I have some object, and when it's outside of water, its weight is 10 newtons. When I submerge it in water-- I put it on a weighing machine in water-- its weight is 2 newtons.

What must be going on here? The water must be exerting some type of upward force to counteract at least 8 newtons of the object's original weight.

That difference is the buoyant force. So the way to think about is that once you put the object in the water-- it could be a cube, or it could be anything.

We know that we have a downward weight that is 10 newtons, but we know that once it's in the water, the net weight is 2 newtons, so there must be some force acting upwards on the object of 8 newtons. That's the buoyant force that we learned about in the previous video, in the video about Archimedes' principle.

## What does buoyant force mean?

This is the buoyant force. So the buoyant force is equal to 10 minus 2 is equal to 8. That's how much the water's pushing up. And what does that also equal to?

That equals the weight of the water displaced, so 8 newtons is equal to weight of water displaced. What is the weight of the water displaced? That's the volume of the water displaced times the density of water times gravity.

What is the volume of water displaced? It's just the volume of water, divide 8 newtons by the density of water, which is 1, kilograms per meter cubed.

A newton is 1 kilogram meter per second squared. If we look at all the units, they actually do turn out with you just ending up having just meters cubed, but let's do the math. We get 8 divided by 1, divided by 9. Just knowing the difference in the weight of an object-- the difference when I put it in water-- I can figure out the volume.

This could be a fun game to do next time your friends come over. Weigh yourself outside of water, then get some type of spring or waterproof weighing machine, put it at the bottom of your pool, stand on it, and figure out what your weight is, assuming that you're dense enough to go all the way into the water.

You could figure out somehow your weight in water, and then you would know your volume. You could just figure out how much the surface of the water increases, and take that water away.

Just knowing how much the buoyant force of the water was or how much lighter we are when the object goes into the water, we can figure out the volume of the object.

This might seem like a very small volume, but just keep in mind in a meter cubed, you have 27 square feet. If we multiply that number times 27, it equals 0. So this is actually 34 square inches. The object isn't as small as you may have thought it to be. It's actually maybe a little bit bigger than 3 inches by 3 inches by 3 inches, so it's a reasonably sized object.

Anyway, let's do another problem. Let's say I have some balsa wood, and I know that the density of balsa wood is kilograms per meter cubed. I have some big cube of balsa wood, and what I want to know is if I put that-- let me draw the water. I have some big cube of balsa wood, which I'll do in brown.The formula to calculate buoyant force (FB) states that the upward force exerted on an immersed object is equal to the density (ρ) of the fluid multiplied by both the fluid’s displaced volume (V) and the gravitational acceleration (g), or FB = ρ x V x g.

The name of this upward force exerted on objects submerged in fluids is the buoyant force. So why do fluids exert an upward buoyant force on submerged objects? It has to do with differences in pressure between the bottom of the submerged object and the top. In physics, buoyancy (/ ˈ b ɔɪ. ə n s i, ˈ b uː j ə n-/) or upthrust, is an upward force exerted by a fluid that opposes the weight of an immersed object.

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In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the pressure at the bottom of a column of fluid is greater than at the top of the column. The formula to calculate buoyant force (FB) states that the upward force exerted on an immersed object is equal to the density (ρ) of the fluid multiplied by both the fluid’s displaced volume (V) and the gravitational acceleration (g), or FB = ρ x V x g.

This calculator was created by user's request. He needs to find a weight of body in liquid. Here comes the Archimedes' principle: The buoyant force on a submerged object is equal to the weight of the liquid displaced by the object.

In physics, buoyancy (/ ˈ b ɔɪ. ə n s i, ˈ b uː j ə n-/) or upthrust, is an upward force exerted by a fluid that opposes the weight of an immersed object.

In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the pressure at the bottom of a column of fluid is greater than at the top of the column.

Buoyant force example problems (video) | Khan Academy