# I need help

1. Feb 26, 2009

### coffeekwok

I need help!!...

Hi all, I'm new to this forum. I just joined the forum and I hope that you guys could help me out.

I'm in the trading business of cookware. I'm currently studying the European standards for these items and there's a point in the standard that I don't understand at all.

It says:
The design of the lid shall be such that it shall be possible to remove it from the body using a force equal to the weight of the lid +2N in any position at a temperature of 23C +/=5C.

It may sounds stupid to you but I'm not a scentist and certainly not very good at Maths. I believe that N stands for Newton but I do not have a clue of what it means be "using a force equal to the weight of the lid +2N."

I have a meeting coming up next week and your help would be highly appreciated. Thank you so much for your help!

2. Feb 26, 2009

### alxm

Re: I need help!!...

Newtons (N) is the standard unit of force. When forces are given as weights (pounds is often used in the US), then they mean the force of gravity exerted by something with that weight.

The conversion factor here is g (9.8). So the (mass in kg) x 9.8 = force in Newtons.
So in total, m x 9.8 + 2 Newtons.
Or you could convert the two the other way, and it'd be the equivalent of lifting the lid + 204 grams

3. Feb 26, 2009

### coffeekwok

Re: I need help!!...

Thanks Alxm! But sorry may be I'm too stupid, I still don't quite understand... do you mean that the lid of the cookware cannot heavier than 204 gram according to the standard?

4. Feb 26, 2009

### alxm

Re: I need help!!...

Sorry if I was unclear. No I divided the added value (2 Newtons) by 9.8 so I got the force-equivalent weight in kilograms (2/9.8 = 0.204).

So, if you express that additional force of 2N in terms of weight, then the force required to lift the lid needs to be the force equivalent of putting 204 grams of weight on top of the lid. (obviously the force needed to lift the lid has to be _at least_ the weight of the lid. Or it won't lift!)

5. Feb 26, 2009

### CompuChip

Re: I need help!!...

If you want to lift any object with some mass (m), then you need to exert a force equal to it's weight (at the very minimum), which is 9.81 x m Newtons. This is simply a consequence of the laws of physics (you need to act against gravity, so your force must be equal or greater to the force with which the earth pulls on it to lift it).

However, I suppose that in the case of a lid, you may need extra force. For example, there may be friction; if the metal lid expands due to heat, it might be harder to lift it; when the lid closes off the pan completely, a pressure difference may arise between the air inside and outside the pan which makes it harder to lift, etc.
I suspect that what the standard is saying, is that the lid should be designed such that due to all these possible effects, one shouldn't have to exert an extra force (on top of the force needed to overcome gravity) of more than 2N to lift the lid.

Yet in other words, if your lid weighs 500 grammes on a scale, and you try to pull it of with a force meter while cooking, you should be able to lift the lid with less than (500 x 9,81 + 2) = 4907 N.

6. Feb 26, 2009

### coffeekwok

Re: I need help!!...

Thanks CompuChip and Alxm! I'm getting there now.

The weight of the lid is 350gram, so in other words I would assume the calculation would be (350 x 9.81 +2) = 3,435.5N.

My next question would be how could I measure that and how do I know whether the design of the lid is correct or not. Thanks!

7. Feb 26, 2009

### Phrak

Re: I need help!!...

You want your answer in pounds, I'm sure. You have to lift the weight of the lid itself plus 9 pounds of force or less, that's all.

Since things get stickier or looser depending on temperature, they want this to happen when tested at 73 degrees F.

8. Feb 26, 2009

### alxm

Re: I need help!!...

No, the weight has to be in kilograms, so 0.35*9.81 = 3.43 add 2 to that = 5.43.
Makes more sense doesn't it? If it took 3500 Newtons to lift the lid, 2 N wouldn't make much difference now would it?

Well, you could buy a force gauge. But a cheap one is really just the same thing as a scale, since I just explained how weight in kg relates to forces. So as I said, 2 Newtons is equivalent to the weight of 204 grams. So the total force (in terms of weight) would be 350+204 = 554 grams. So what you can do, is borrow a fishing scale (a good kind, the cheap ones are rubbish), attach the hook to the lid with a string or directly, and check that the scale doesn't go above 554 grams before the lid pops off.

9. Feb 26, 2009

### alxm

Re: I need help!!...

How did you arrive at 9 pounds for 2 newtons?

10. Feb 26, 2009

### Mastertje

Re: I need help!!...

I think the best thing for you to do is, find a company nearby that has a universal testing machine; http://en.wikipedia.org/wiki/Universal_Testing_Machine

This machine can measure force and displacement extremely accurately, and if it has a temperature control box installed you can also measure at the temperature required for the standard!

11. Feb 26, 2009

### timmay

Re: I need help!!...

If you can find a local company who will do the testing it's pretty trivial, assuming they have a set of grips that will fit and a load cell accurate enough to measure that small a force. You might even be able to find a local university where a kind lab manager might do the tests for you on the cheap. And 23 +/- 5C is pretty universal room temperature in most of northern Europe (funnily enough where most of these standards are contributed from, either DIN or BSI!) so you probably won't even need the temperature chamber.

12. Feb 26, 2009

### Phrak

Re: I need help!!...

By making an error? I multiplied by 4.5 instead of dividing.

13. Feb 26, 2009

### zoobyshoe

Re: I need help!!...

A force of one Newton is about the same as the weight of an average apple.

Spooky.

14. Feb 27, 2009

### coffeekwok

Re: I need help!!...

Thanks Alxm and all!

I got it ... I think I will get a spring scale to test the lid... I saw one on the web it could measure up to 10N....