# Homework Help: Buoyant force question

1. Jul 22, 2004

### akatsafa

If two objects are the same shape and have the same dimensions, but one object has a bigger density, does that affect the buoyant force? Will the object with a bigger density have a greater buoyant force? They're both immersed in water.

I say no because the buoyant force depends on the volume of fluid displaced and the density of the liquid. Since I don't know whether the objects are more or less dense than water, then the density of the objects wouldn't matter, right?

2. Jul 22, 2004

### faust9

If two objects have the same volume but one is made of a more dense substance how does that affect the mass of said object? How does the bouyant force relate to volume displaced? Which body will displace more liquid?

I'd recommend delving into the above questions then when you have an answer go here: http://www.walter-fendt.de/ph11e/buoyforce.htm [Broken] play around with the density only and see how the bouyant force changes.

Good luck.

Last edited by a moderator: May 1, 2017
3. Jul 22, 2004

### akatsafa

I went to the website and changed only the density. It did not affect the buoyant force at all. Thank you. That was a good site!

4. Jul 22, 2004

### faust9

I'm sorry it worked when I first tried it. There seems to be a bug in the applet. It's funny, you can find that applet in dozens of places and each one is broken...

Anywho,

$$F_B=\rho_{water}V_{displaced}g$$

or

$$F_B=m_{object}g$$

Look into archimedes principle. Eurecha!!!

Here: this works a lot better:
http://www.phy.ntnu.edu.tw/java/buoyant/buoyant.html [Broken]

Use the mouse to pick the grey block on the right up and place it in the water. The density is initiall 2. The block sinks. There is a label below the textfields that indicates bouyant force. Now play with the density. If density is made less than 1 the block will float. wath bouyant force. If density is greater than 1 the block sinks. Watch the force. The block will bob up and down a few times but eventually stabilize.

Here's another one. Select different materials (don't change the volume) and watch the change in buoyant force. http://www.xmission.com/~locutus/applets/Buoyancy.html

Hopefully everything will work correctly this time.

Good Luck.

Last edited by a moderator: May 1, 2017
5. Jul 22, 2004

### akatsafa

I used the first site, but I'm still a little confused. If I don't put a density less than one in the space, the buoyant force is the same. I put in 4 and then 10, it showed that the buoyant force was the same, but when I put less than one, it showed a smaller buoyant force. The question that I was asked was just if a bigger density made a larger buoyant force than a smaller density. It never specified if it was less than one, so how should I answer this question?

6. Jul 23, 2004

### faust9

What happend to the block when you had a density greater than 1 (ie greater than the density of the fluid)? Now compare that to what happened to the block when density was less than 1 (ie less than the density of the fluid)? The block behaved differently in both situations.

I presented two equations each of which corresponds to the response of the block. If you think about it (analyze what is happening with the buoyant force for various densities above and below 1).