So my friend and I are working on an engineering project to create a better oil dipstick and all of our best designs utilize a tube that is emersed in fluid and the top is capped. In testing, this idea works well and fluid level is maintained for water, but not oil. Motor oil weighs less than water, so why does it escape the vacuum?

Edited November 3, 20169 yr by Keegenmould

What vacuum?

The vacuum that holds the water up in the tube. The vacuum created from sealing the tube.

I think what you are seeing is due to a difference in polarity.

 

Water is polar, Oil is non-polar.

 

The physics are otherwise the same for both, atmospheric pressure counteracting gravity. Liquid wants to fall, air wants to get in.

 

Water is like a group that hangs out together, while oil is more about going out and meeting those nice air molecules across the way.

 

One idea would be to look at utilizing a number of smaller tubes at the end. Possibly higher viscosity(cooler in this case) oil could work as well. May also want to look at roughening up the tube's interior(or using tubes made of a different material).

 

 

It may be a surface tension effect, which I think is related to the polar nature of water Endy mentions. Water tends to bead up. Oil, not as much. There is also surface adhesion to worry about. If the liquid can creep up the sides of the tube it will be able to fill it up.