![]() ![]() This was for a larger machine in a slightly faster flow, but I thought my values had to be in this ball park. You are exactly correct, in that I was looking at a hand calc example from my predecessor, and I was taking it as gospel, when in fact he was confusing specific weight and density. I hope this Thank You very much for your input, and sorry for the delay - I'm just super busy, trying to get this report completed for a project submittal. Yes - I wish the US would just drop this terrible unit system once and for all! The correct drag force should be about 30 lbf. Recall the numeric value of 1 pound of mass weighs (has a force of) 1 pound and is only valid in earth's gravity. The mass density of water is 62.4 pounds mass/ft^2. If you simply change the gamma unit tag in example #2 from "lbf" to "lb", you will get the correct result. Update - the equation you used for the drag force requires a mass density, not weight density.the Mathcad Prime result supports this. I've used this approach many times with great success. Rumor has it Prime 7 will have some controls.maybe a simple drop-down like we have in v15. You will need to standardize on a "density" unit and account for gravity, or not, in your equation.Īlternatively, if you use Mathcad 15, you could create a drop-down unit choice and use an "If" statement to set the equation up to handle the units based on user selection. So a balloon filled with helium is less dense than one filled with air, because helium atoms are lighter than the atoms in air.As you know, a "slug" is a different unit from a "lbf", so you can't use the same equation for both and expect consistent units for a result. Solid ice is less dense than liquid water, because the particles must pack together more closely in the liquid.īut even substances in the same state can have different densities, depending on the mass of the atoms that make them up. Interestingly, water is an exception to this rule. In gases the particles are far apart, moving quickly in random directions with a lot of empty space between them. Liquids typically have a lower density than solids. In liquids, the particles can move around more freely, so they slide over each other with some gaps between them. In a solid, the particles are tightly packed, so you can get a lot in a given space. The difference is mostly due to the fact that air is a gas and the water is a liquid, because density depends a lot on the state of matter. So density is mass divided by volume, five hundred grams divided by five hundred cubic centimetres, giving one gram per cubic centimetre.īut this air-filled balloon has a much lower density of about zero point zero zero one gram per cubic centimetre. ![]() This has gone up by five hundred cubic centimetres, so that’s the volume. You can find the volume of an irregular shaped object by submerging it in water and measuring how much this level changes. You can think of density as how heavy something is for its size.And you can calculate it by taking the mass - this is five hundred grams - and dividing it by the volume. I know which I’d prefer to try and catch! And that’s because water and air have different densities. These balloons are the same size, but this one is filled with water instead of air and is much heavier.
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