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>What is the apparent weight of a 70 kg person in water?
I think we're getting closer to an answer...but the question is still vague.
Salinity of the water affects buoyancy. More salt = more flotation. People can float better in the Salton Sea.
Body volume affects buoyancy. More volume = more flotation. (That's where body fat comes into play...lower density.)
Air in your lungs (obviously) will increase buoyancy.
Any SCUBA divers here? They need to factor buoyancy and carry extra lead weights for deep dives.
fat density = 0.92 g/ml
fresh water density = 1 g/ml
salt water density = 1.025 g/ml
muscle density = 1.06 g/ml
Without dissecting your body, or making fancy guesses, you could just measure your displacement volume. Not easy...but more accurate.
Find a large enough container and a helper:
Fill with water. Get in. Submerge yourself completely. Mark the water level. Get out (don't splash water out). Mark the level.
With a known volume containers (5 gal bucket & 1 gal jug), refill until you reach the high mark.
1 gallon = 3,785 ml
1 pound = 454 g
So, the density of a 150# person displacing 17-3/4 gallons:
body density = 68,039g / 67,183ml
subtract 1.00 g/ml for fresh water density
multiply again by your volume of 67,183 ml
= 856 g = 1.9 pounds.
So, if you hold the same amount of air in your lungs, you'll have negative buoyancy of 1.9 pounds in fresh water. You'd sink slowly. Flapping your hands would be enough to keep you afloat.
In salt water:
body density = 68,039g / 67,183ml
subtract 1.06 g/ml for fresh water density
multiply again by your volume of 67,183 ml
= -3175 g = - 7.0 pounds.
Your sinkability is negative 7 pounds...meaning you'd float without any assitance.
My life vest provides positive buoyancy of around 15-20 pounds. Enough to keep you afloat in fresh or salt water. If you're a freakishly muscular person with low body fat, you might consider a larger vest.
I think we're getting closer to an answer...but the question is still vague.
Salinity of the water affects buoyancy. More salt = more flotation. People can float better in the Salton Sea.
Body volume affects buoyancy. More volume = more flotation. (That's where body fat comes into play...lower density.)
Air in your lungs (obviously) will increase buoyancy.
Any SCUBA divers here? They need to factor buoyancy and carry extra lead weights for deep dives.
fat density = 0.92 g/ml
fresh water density = 1 g/ml
salt water density = 1.025 g/ml
muscle density = 1.06 g/ml
Without dissecting your body, or making fancy guesses, you could just measure your displacement volume. Not easy...but more accurate.
Find a large enough container and a helper:
Fill with water. Get in. Submerge yourself completely. Mark the water level. Get out (don't splash water out). Mark the level.
With a known volume containers (5 gal bucket & 1 gal jug), refill until you reach the high mark.
1 gallon = 3,785 ml
1 pound = 454 g
So, the density of a 150# person displacing 17-3/4 gallons:
body density = 68,039g / 67,183ml
subtract 1.00 g/ml for fresh water density
multiply again by your volume of 67,183 ml
= 856 g = 1.9 pounds.
So, if you hold the same amount of air in your lungs, you'll have negative buoyancy of 1.9 pounds in fresh water. You'd sink slowly. Flapping your hands would be enough to keep you afloat.
In salt water:
body density = 68,039g / 67,183ml
subtract 1.06 g/ml for fresh water density
multiply again by your volume of 67,183 ml
= -3175 g = - 7.0 pounds.
Your sinkability is negative 7 pounds...meaning you'd float without any assitance.
My life vest provides positive buoyancy of around 15-20 pounds. Enough to keep you afloat in fresh or salt water. If you're a freakishly muscular person with low body fat, you might consider a larger vest.
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According to Archimedes' Principle you weigh the same its just that your body moves the water out of the way, and the water pushes upward as your body pushes downward. Making it seem that you are lighter. Its not that your weight changes its just that displacement and buoyancy are added to the equation.
source(s):
Own knowledge.
Own knowledge.
You weight is the same in the water or on land. Your body fat has no bearing on on your weight in either case.
To answer this question, it's necessary to differentiate between mass, weight and apparent mass.
When you say 70 kg, you're obviously referring to mass when you use the unit kg. Since mass is amount of matter an object contains, it doesn't vary with the location of an object.
When talking about weight, it means the force of gravitational pull on an object. On Earth, the force varies with the distance of the object from the centre of the Earth. Submerging an object in water doesn't change this distance much, so the weight can be said to remain the same.
Mentioning apparent weight, then upthrust (the force exerted by water) has to be taken into account.
Apparent weight = Weight - Upthrust
The upthrust depends on the density of an object. In the human body, more body fat means a lower density and a higher upthrust, hence lower apparent weight.
When you say 70 kg, you're obviously referring to mass when you use the unit kg. Since mass is amount of matter an object contains, it doesn't vary with the location of an object.
When talking about weight, it means the force of gravitational pull on an object. On Earth, the force varies with the distance of the object from the centre of the Earth. Submerging an object in water doesn't change this distance much, so the weight can be said to remain the same.
Mentioning apparent weight, then upthrust (the force exerted by water) has to be taken into account.
Apparent weight = Weight - Upthrust
The upthrust depends on the density of an object. In the human body, more body fat means a lower density and a higher upthrust, hence lower apparent weight.
What is the apparent weight of a 70 kg person in water?
Well there is no exact answer, because it depends on the size of the person and the amount of fat in his body, which is necessary to find his density. Two 70 kg persons may have the same weight, but due to their different density, have different apparent weight.
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(body density - water density) * volume displace = weight in water
Is this the formula?
Basically,
body density - water density * body volume