# Relationship between upthrust and density of iron

### density - What property of objects allow them to float? - Physics Stack Exchange

Thus, a ship, even if it is made out of high-density iron it is full of air. An object floats if its upthrust (buoyancy) is in equilibrium with its downwards More specifically, it is the relationship between the two; the density of the. Upthrust is proportional to the density of the fluid. arkofnoah, Aug 9, Hence find the ratio of Pseawater/Pfreshwater in terms of y and z. 1 a body of volume cm 3 is immersed completely in water calculate the upthrust on the body density of water 10 3kg m 3 g 98m s 2 2a piece of iron o g8fl7ss.

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.

## Floating and sinking

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. 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?

**How Do Ships Float?**

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.

## Archimedes' principle

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. So I have a big cube of balsa wood and the water should go on top of it, just so that you see it's submerged in the water.

When increasing speed or driving in a curve, the air moves in the opposite direction to the car's acceleration. However, due to buoyancy, the balloon is pushed "out of the way" by the air, and will actually drift in the same direction as the car's acceleration.

### Resources for Teaching Science | Floating and sinking

When an object is immersed in a liquid, the liquid exerts an upward force, which is known as the buoyant force, that is proportional to the weight of the displaced liquid. The sum force acting on the object, then, is equal to the difference between the weight of the object 'down' force and the weight of displaced liquid 'up' force. Equilibrium, or neutral buoyancy, is achieved when these two weights and thus forces are equal.

Refinements[ edit ] Archimedes' principle does not consider the surface tension capillarity acting on the body. However, the concept of Archimedes' principle can be applied when considering why objects float.

Proposition 5 of Archimedes' treatise On Floating Bodies states that: Any floating object displaces its own weight of fluid. Thus, only in the special case of floating does the buoyant force acting on an object equal the objects weight.

Consider a 1-ton block of solid iron. Suppose the same iron block is reshaped into a bowl. It still weighs 1 ton, but when it is put in water, it displaces a greater volume of water than when it was a block.

The deeper the iron bowl is immersed, the more water it displaces, and the greater the buoyant force acting on it. When the buoyant force equals 1 ton, it will sink no farther.