Purpose:

Recently we have been exploring forces and hanging chains. We looked a variety of settings for this always starting with force pictures. For this lab we are going explore a setting that involves forces due to surface tension sometimes called capillary forces. The core concept is that the water "hanging" below a certain point on the surface is being supported like a chain of some mass. I will be providing a little less guidance in this lab so you can experience the challenge of creating a process that allows us to try to answer a question we're interested in. The question is this: Does the force lifting the water up between the plates change with the changing separation of the glass plates?.

• I) Process Description: Put a little water in the petri dish (don't worry it's clean). Take two glass slides (handle by the edges) and stand them in the water. One pair of vertical edges you will hold firmly together the other you will use a bamboo skewer to hold the slides apart. You have created a gap between the slides that has a "thin" end where they are held together and a "thick" end where the bamboo skewer holds them apart. You will find that the water is "sucked up between the slides" and forms a curved shape between the slides.

• II) Data Generation: When you carefully lift the slides out of the water the shape of the water between the glass plates will not change. You can now trace the shape of the water on the glass with a marker. Remember to also mark the level of the water in the dish on the slide. Now, using a ruler, measure the height that the water was lifted at the thick end, middle, and thin end, as well as how far these points are from the thin end of the gap. You also need to know the thickness of the bamboo skewer.

• III) Force Picture: At the location of the "middle" measurement draw a picture of the column of water that is being supported by unknown forces and sketch the forces acting on that column of water. What shape is that column of water? How is this like the hanging chain problem?

• IV) Mass of Water: The mass of water forms a roughly square column of some height, width and thickness. If we can calculate the volume of that column then we can figure out it's mass using the densit of water as 1.0 gr/cm3. The challenge is figuring out how thick the water is at that point. To do this draw a cross section of the gap between the slides and label the separation between the slides at each end. Using your knowledge of proportional triangles figure out the thickness of the water at the "middle". Once you know this you can calculate the mass and from that the force of gravity which must be the same as the mystery force.

• V) Repeat for thick and thin: If you repeat this calculation for the thick end of the gap and the thin end of the gap (where the water doesn't quite make it to the top of the slide. Now you can answer the question based on your data and analysis.

LAB DELIVERABLES (turn in):

An introduction and 5 (or more) paragraphs describing your data and calculations for each of the steps above. In each section present any actual measurements, explanations and descriptions of the task you are working on, calculations that you make, and comments on the results.