Iron and plumbum (lead) on a balance in air and water

In summary, when the aquarium is filled with water, the balance is still in equilibrium because the weight of the lead is balanced by the buoyant force acting on it, which is equal to the weight of the water displaced. This is due to the principles
  • #1
martijn-arts
5
0
On the flat bottom of an aquarium is an old fashioned balance. On one scale of the balance is a piece of plumbum, on the other side is a piece of iron. The scales are exactly in balance.
Now we let the aquarium fill slowly with water, until the entire balance is under water. What happens now:
A The scale with plumbum drops
B The scale with iron drops
C The scales remain in balance
 
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  • #2
welcome to pf!

hi martijn-arts! welcome to pf! :smile:

(btw, the ancient romans called it "plumbum", but we call it "lead" :wink:)

tell us what you think (and why), and then we'll comment! :smile:​
 
  • #3


Thanks!

I think lead because of the difference in kg/dm^3 of lead and iron and that of water.
Lead => 11.3 kg/dm^3
Iron => 7.86 kg/dm^3

This is both in air. Water is 0.998 kg/dm^3

Am I on the right track?
 
  • #4


By the way, this should be the perfect question for you, looking at your profile picture :)
 
  • #5
hi martijn-arts! :smile:
martijn-arts said:
By the way, this should be the perfect question for you, looking at your profile picture :)

yes, i used to have one of those in my little bowl …

it's one of the reasons i eventually studied fishics! :wink:​
martijn-arts said:
Thanks!

I think lead because of the difference in kg/dm^3 of lead and iron and that of water.
Lead => 11.3 kg/dm^3
Iron => 7.86 kg/dm^3

This is both in air. Water is 0.998 kg/dm^3

Am I on the right track?

yes, it's certainly the density that makes the difference

maybe you're right and maybe you're wrong …

what is your laws-of-physics reason for saying that the greater density should push the scale down more? :smile:​
 
  • #6


That's where I got stuck and my knowledge was too old (it's been 10 years)
 
  • #7
aha! :biggrin:

ok, apply the principles of buoyancy …

what are the forces on the lead (if it isn't moving), and so what is the force the lead exerts on the scale? :smile:​
 
  • #8


To be honest: I do not really understand buoyancy because of my knowledge of English.

Would you please be so kind to give the right answer with the reason
 
  • #9
martijn-arts said:
To be honest: I do not really understand buoyancy because of my knowledge of English.

Would you please be so kind to give the right answer with the reason

sorry, martijn-arts, on this forum we don't just give the answer

look up "bouyancy" (or "bouyant force") in wikipedia or the pf library

the important thing is that there is an extra force on the lead (the bouyant force), which acts through the centre of gravity of the displaced water
 

1. What is the difference between iron and plumbum (lead)?

Iron and plumbum (lead) are both metallic elements on the periodic table. Iron is a transition metal with the symbol Fe and has a grayish-white color. Plumbum, also known as lead, is a post-transition metal with the symbol Pb and has a bluish-white color. They have different properties and uses, but both are commonly found in various industries and products.

2. How does iron and plumbum (lead) react on a balance in air?

When iron and plumbum (lead) are placed on a balance in air, they will have different reactions due to their different properties. Iron is more reactive and will rust when exposed to oxygen, while plumbum is less reactive and will remain unchanged in air. This is because iron has a higher tendency to form compounds, while plumbum is relatively stable.

3. How does water affect the weight of iron and plumbum (lead)?

Water can have a significant impact on the weight of iron and plumbum (lead). Iron will also react with water, forming iron oxide (rust), which will increase its weight. Plumbum, on the other hand, is insoluble in water and will not be affected by it. However, if the water contains other substances that can react with plumbum, its weight may be altered.

4. Can iron and plumbum (lead) be accurately measured on a balance?

Yes, both iron and plumbum (lead) can be accurately measured on a balance. However, it is important to consider the conditions in which they are being measured, such as in air or water. The reaction of iron and plumbum (lead) in these environments can affect their weight, so it is essential to take this into account when measuring them.

5. What are the potential health hazards of working with iron and plumbum (lead)?

Both iron and plumbum (lead) can be hazardous to health if not handled properly. Iron can cause lung irritation and damage if inhaled in large amounts, while plumbum (lead) is toxic and can accumulate in the body over time, leading to various health issues. It is important to follow safety protocols when working with these elements to minimize potential risks.

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