Lid Pressure at Sea & Denver

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In summary, the pressure inside a box with a lid can be used to calculate the force required to lift the lid. In a specific example, a box with dimensions 10cm x 20cm x 8cm and inner pressure of 72000 Pa requires a force of 586.5 N to lift the lid at sea level. In Denver, where the atmospheric pressure is 67.5 kPa, the excess pressure inside the box would cause the lid to pop off, requiring no additional force to remove it. Therefore, the force required to lift the lid in Denver would be 0 N.
  • #1
Pressure of a lid!

Homework Statement



A lid is put on a box that is 10cm long, 20cm wide and 8cm tall and the box is then evacuated until its inner pressure is 72000 Pa.

1.How much force is required to lift the lid at sea level?

2. How much force is required to lift the lid in Denver on a day when the atmospheric pressure is 67.5 kPa (2/3 the value at sea level)?

Homework Equations



P=F/A

A=L x W


The Attempt at a Solution



I got #1 where I did the following:

A= L x W= 0.1 x 0.2= 0.02m^2

P=F/A
(101325 - 72000)= F/ 0.02
586.5 N= F

I attempted to do #2 as shown below and got both methods wrong:

so first I did: P=F/A
(67500- 72000)= F/0.02
-90N= F (wrong answer)

so then I did: P=F/A
67500= F/0.02
1350N= F (wrong answer again)

I am unsure how to answer this question, so any help is appreciated! It's online homework so there's no given answer either. thanks!
 
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  • #2


Your first attempt at #2 is along the right lines, you just didn't analyze the result closely enough. Suppose the lid were secured in place with some kind of fastener. If the pressure inside is higher than outside, what would happen when you undid the restraints? If there were no restraints in place when the outside pressure dropped below the inside pressure, what would happen to the excess pressure in the box?
 
  • #3


so if you undid the restraints then the pressure inside would decrease? I'm still confused on how to solve the problem.
 
  • #4


Look at the data: where is the pressure higher, inside or outside? What happens to a lid if the pressure inside the container is higher than the outside pressure? Do you have no kitchen experience with boiling milk in a covered pot? :wink:

ehild
 
  • #5


no kitchen experience at all! but if the pressure inside the container is higher than the outside, wouldn't the lid pop off? I still don't get how this will help me get the question...
 
  • #6


warrior2014 said:
no kitchen experience at all! but if the pressure inside the container is higher than the outside, wouldn't the lid pop off? I still don't get how this will help me get the question...

Think it through. If the lid pops off by itself, how much force is required to remove the lid?
 
  • #7


Oh okay I get it. thank-you for all of your help :)!
 

What is lid pressure?

Lid pressure refers to the pressure exerted on the lids of containers or bottles due to changes in altitude or atmospheric pressure. This can affect the seal of the container and potentially cause leaks or spills.

How does lid pressure change at sea level compared to Denver?

Lid pressure at sea level is higher compared to Denver due to the difference in altitude. At higher altitudes, the atmospheric pressure is lower, resulting in less pressure on the lids of containers. This can cause containers to bulge or deform.

What are the potential risks of lid pressure changes at sea and Denver?

The main risk of lid pressure changes is the potential for leaks or spills. This can be especially problematic for containers that hold liquids or gases, as changes in pressure can cause them to expand or contract. In some cases, this can also affect the shelf life of products.

How can lid pressure be managed at sea and Denver?

To manage lid pressure at different altitudes, it is important to choose containers with sturdy and reliable lids. It is also recommended to release excess pressure before opening containers, especially at higher altitudes. Additionally, keeping containers in a temperature-controlled environment can help mitigate pressure changes.

What other factors can affect lid pressure besides altitude?

Besides altitude, temperature can also affect lid pressure. Changes in temperature can cause the air inside a container to expand or contract, resulting in changes in pressure. Other factors such as humidity and air pressure can also play a role in lid pressure changes.

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