# Help identifying a length for this paper edge

Gold Member
Hi PF!

Two years ago my lab launched experiments aboard the ISS. The experiment was simple: place two water droplets on a substrate, set camera above the drops, and watch them coalesce. However, the exact size of the drops is unknown (approximately 1 cm radii, though this number is debated). So I'm analyzing this data and have done A TON of work to try and back out a length scale, but no two metrics agree within 5% of each other, so I'm not overly confident. Now I may have to scrap the entire project, but before I do, this might be the key: does anyone know the size of the corrugated "jagged triangles" at the end of this wipe being used to dry the surface? An astronaut is holding it, and the drop is total about 20 mL volume (few cm long) to give you a guess.

Gold Member
Edit: I just found something and I THINK each triangle base might be 15/37 = 0.405 cm. But let me know what you think.

Mentor
How could we possibly be able to answer this? Ask the astronaut.

But in the future, put a measurement scale in the experiment and record the specs/dimensions of the camera.

Wrichik Basu, robphy and BillTre
Mentor
If that is a standard three panel brown paper towel, then (as far as I know) all use the same number of teeth per inch. It's called a serrated cut, and was the standard cutoff on towel folders up to about 15-20 years ago. Check out the local public restrooms for paper towels. You might get lucky.

The industry got away from serrated cutoffs because newer, tougher towel material is difficult to cut using serrated cutoffs. Much of my engineering career was working with cutoff systems.

joshmccraney
Gold Member
How could we possibly be able to answer this? Ask the astronaut.

But in the future, put a measurement scale in the experiment and record the specs/dimensions of the camera.
I wasn't in the control room. Wasn't even supposed to be my experiment, but my advisor sadly passed away, leaving the project for me to handle.

But regarding how to answer this: I think I found a solution so...

Gold Member
If that is a standard three panel brown paper towel, then (as far as I know) all use the same number of teeth per inch. It's called a serrated cut, and was the standard cutoff on towel folders up to about 15-20 years ago. Check out the local public restrooms for paper towels. You might get lucky.

The industry got away from serrated cutoffs because newer, tougher towel material is difficult to cut using serrated cutoffs. Much of my engineering career was working with cutoff systems.
This is helpful! What do you think of this?

Gold Member
Okay, so I'm pretty sure the triangle bases are 4,5, or 6 mm long. Like, 100% sure, but which...

Staff Emeritus
Gold Member
You said no two methods agree within 5% of each other, but if they all agree within 15% of each other, you can figure it out by process of elimination

Gold Member
Any reason you can't show us any other pics? You've got enough video to do your experiment, so you can get more pics, but maybe we'll see something in them that you've missed.

Mentor
I find it hard to believe NASA doesn't know what exact materials were present on/available on/sent to ISS.

Wrichik Basu and BillTre
Gold Member
I find it hard to believe NASA doesn't know what exact materials were present on/available on/sent to ISS.
These experiments were conducted in late 2020. The wipe they used was not in our payload. I have absolutely no clue how to ask them for this info.

Gold Member
Any reason you can't show us any other pics? You've got enough video to do your experiment, so you can get more pics, but maybe we'll see something in them that you've missed.
Sadly each video was about 1 minute. This is literally the only shot I have (well, a 3 second clip)