Surface Tension, find number of stitches to be made

[Ishraq Begum]

Homework Statement

The tension in the skin of the left ventricle of heart is 4.90 N/m. A cut is made on the left ventricle during surgery. How many stitches must be used to repair the cut? Each stitch will safely support a tension of 0.4 N.

Homework Equations

Surface tension = force/length

The Attempt at a Solution

Total surface tension = 4.90 N/m
Length = 2 x 4 x 10^-2 m
n = number of stitches
n = 4.90 x 0.08/0.4
I'm sure that's not correct

 

[haruspex]

Length = 2 x 4 x 10-2 m

Where does this come from?

 

[Ishraq Begum]

Where does this come from?

I don't really know, I'm confused. I thought when force due to surface tension acts on an object, it acts on both the sides of it.

 

[haruspex]

I don't really know, I'm confused. I thought when force due to surface tension acts on an object, it acts on both the sides of it.

No, I mean where does your length information come from. I do not see any in the problem statement. Is it a 4cm cut?
Are you sure your other data are correct? They imply you only need a stitch every 8cm, which is much too far. Perhaps only 0.04N per stitch?

 

[Ishraq Begum]

No, I mean where does your length information come from. I do not see any in the problem statement. Is it a 4cm cut?
Are you sure your other data are correct? They imply you only need a stitch every 8cm, which is much too far. Perhaps only 0.04N per stitch?

I'm pretty sure the question is correct.

 

[haruspex]

I'm pretty sure the question is correct.

You still have not answered my question about how you got this equation.

Length = 2 x 4 x 10-2 m

It looks like you have information that something is 8cm long, but there is nothing matching that in your problem statement. Did you leave something out?

 

[Ishraq Begum]

You still have not answered my question about how you got this equation.

It looks like you have information that something is 8cm long, but there is nothing matching that in your problem statement. Did you leave something out?

The length equation, I'm not sure if its correct. I was taught that when surface tension acts on a object, it acts on both the sides of an object. Therefore I multiplied 2 with the length of the cut.

Oh, I'm so sorry. I forgot to mention the length of the cut. Here's the complete question:

The tension in the skin of the left ventricle of heart is 4.90 N/m. A 4 cm cut is made on the left ventricle during surgery. How many stitches must be used to repair the cut? Each stitch will safely support a tension of 0.4 N.

 

[haruspex]

Therefore I multiplied 2 with the length of the cut.

The tension in the stitch also acts on both sides, so no need to multiply by two.

 

[Ishraq Begum]

The tension in the stitch also acts on both sides, so no need to multiply by two.

Okay. How do I proceed after that?

 

[haruspex]

Okay. How do I proceed after that?

I'm not at all sure. It depends on how advanced the question is supposed to be.
Taken at a very simple level, I do your calculation, but without the x2, and find one stitch to be just enough. But intuitively that is wrong, which is why I queried the data.
A typical stitch spacing would be only a few mm.

It is intuitively wrong, not because the stitch would give way, perhaps, but because it would not do a very good job of closing the wound. Given the surface tension, you may be able to calculate how wide the gap between the wound edge would be between two stitches at a given separation. But you would need info on how wide the gap is allowed to be.

Can you relate this to anything you have been taught?

 

[George Cosmas]

The Answer here is 29 stitches but I have no idea how to go through it...

 

[haruspex]

The Answer here is 29 stitches but I have no idea how to go through it...

Please clarify.
Are you saying you have been given the identical question and are told the answer is 29?
Or do you have some formula by which you calculate 29, but cannot explain the basis of the formula?
Or... what?