I have a physics problem for you...

[Massacure]

A person lifts up a 24 kilogram barbell. How much force would they need to lift up that same barbell under water?

[ChairmanAgnostic]

1. It depends on how much water it displaces.

It will still be close to 24 kgs.

[Massacure]

3. It doesn't give the volume of the dumbell though.

[tridim]

2. Is it a gigantic 25kg styrofoam barbell?

Or a typical 25kg metal barbell?

[Massacure]

4. It doesn't specify.

I can't possibly think about how to only solve the problem knowing only the mass.

[NNadir]

7. One cannot solve this problem with only the mass, one must assume

the composition of the weight.

One must know the volume, and depending on the degree of accuracy one desires, the temperature of the water.

Assume that the weight is made of carbon steel, which has a density of 7.84 grams per milliliter.

http://216.25.30.233/DataSheets/Densities%20of%20Materials%20Sorted%20By%20Category%20Then%20Density.htm

The volume of the weight is thus m/d where d is the density or 24,000 grams/(7.84 grams/ml) = 3065 ml. (I carried one extra significant figure.) If the water is cold, 3.98C, it will have a density of 1.00 gram/ml and thus the weight of the water is 3065 grams or 3.065 kg.

The force is given by Archimedes principle as F = (w - w(H20)) g where g is the gravitational acceleration. Thus the downward force on the weight is now (24.00 - 3.065) kg * 9.81 m/s^2 = 205.4 newtons, where we have carried an extra significant figure, and taken the gravitational acceleration to be that at an altitude and location at which it is 9.81 m/s. Thus, under such circumstances one would experience the weight as being roughly equivalent to a 21 kg mass.

[HysteryDiagnosis]

5. Not much less than 24kg.... remember, there are boats that weigh

24kg.... and boats float, in that case, it requires 0kg to raise a boat until it achieves it's proper waterline.

[unblock]

6. i think it's effective mass is reduced by the mass of displaced water

that is, imagine that the barbell was magically transmogrified into water instead of metal. how much mass is lost?
the metal barbell is 24kg, let's say the water barbell is 1kg.

that means that the 24kg barbell underwater would act feel like a 23kg barbell above water.

i think. high school physics was a long time ago....

[pinkpops]

8. Why would it change at all? It would have no tendency to float.

[ChairmanAgnostic]

9. the lower you go, the higher the water pressure.

the higher the water pressure, the more likely that the water approaches the density of the item. At some point, the density of water exceeds even tool steel densities, and guess what? the barbell floats. translation, the barbell displaces more water at high densities than its own mass.

check out submarines. They are huge, heavy steel beasts that trim themselves on that same principle. heck, they can even float.

[seriousstan]

11. WHAT? Have you learned a way to compress water? Nobody else has.

Actually, that is technically wrong, you can compress anything but because of the scale of force and compression we are discussing it is commonly stated that liquids are incompressible.
A barbell will never float or even rise in deep water. Dishplates sit on the bottom of the ocean. As for subs, they use compressed air and ballast water to trim underwater.

This may be informative... Submarines: How They Work - Introduction
http://www.onr.navy.mil/focus/blowballast/sub/work1.htm

[northzax]

12. and, as I recall

because water spreads pressure evenly around an object, it would take no more effort to move the barbell at the bottom of the Marianas Trench than in the kiddie pool, right?

[Dead_Parrot]

10. Why?

What are you doing over the weekend, that you need this information for? :)

[oneighty]

13. The lifter's arms

hands and so forth would have to overcome the resistance of the water. Likely it would be a draw.

As an experiment take a hammer and a nail and a pine two by four into your swimming pool and while underwater try to drive the nail through the two by four.

Good luck.

Archimedes Principal; an object immersed in water is buoyed up by the weight of the volume of water it displaces.

One cubic foot of anything displaces 64 pounds of sea water 62.4 pounds of fresh water. (Aprox)

180