Lab #1 Invisible Tension – Part 3 (for formal lab write-up)
Introduction: (this is a continuation of our exploration of the invisible field of tension around rods rubbed with various materials, and your introduction will appropriately introduce this part (part 3) with some relevant observations and background from what we have done so far)
Materials: Plastic and glass rods, cloths of wool, silk, polyester, and rabbit fur, as well as four pieces of scotch tape and an object on which to stick the tape so it hangs freely.
- Take four pieces of scotch tape, approximately four finger-widths in length each, and hang them from the side of your desk (for temporary safe-keeping).
- Take one of the pieces of tape, and fold about ¼ of an inch of one end (sticky-side to sticky-side) back on itself so it forms a ‘blunt’ (square) tab on one end. This is simply done so that we can identify this particular piece of tape as a ‘blunt’ piece.
- Next, take another piece of tape, and fold both the corners of one end in (sticky-side to sticky-side), so that it forms a ‘pointy’ tab on one end, again just so we can identify this particular piece of tape as a ‘pointy’ piece.
- Take the pointy tape and stick its sticky-side to the non-sticky side of the blunt tape, making sure they are well-stuck together, with the tabs at the same end.
- Holding the pointy and blunt tabs firmly, quickly separate the two pieces of tape.
- Rotate your hand that is holding the pointy piece of tape so that you can bring the non-sticky sides of the tape near each other. Observe what happens. (Make sure to record your observations, but after you are done with the rest of the procedures.)
- Now stick the pointy and blunt ended pieces of tape you have in your hands to the straw on your tin-can monster, so that the tapes are hanging with their tab-ends pointing away from the straw. Leave them there.
- Repeat steps 2 – 6.
- Bring the non-sticky side of the second pointy tape near the non-sticky side of the first blunt tape that is hanging from the straw, and then near the non-sticky side of the first pointy tape that is hanging from the straw. Observe what happens in each case, and then stick the second pointy tape to the straw next to the other tapes.
- Repeat step #9 with the blunt tape, bringing it near the already hanging pieces. Observe what happens in each case.
- Now rub a glass rod vigorously with silk, and bring it near the non-sticky sides of all four of the hanging tapes at once, making sure that the tapes do not actually touch the rod. Observe.
- Rub a plastic rod with rabbit fur or wool and repeat step #11. Observe.
- See what happens if you then bring both the ‘charged’ rods near the tapes from a) the same side of the tape at the same time (as if the rods were one single rod) and b) from opposite sides of the tape at the same time.
- Record all your observations.
Analysis: Use information from our class discussion, and think about how you could answer the following questions:
- What does this experiment show us?
- Why do the tapes react differently in various cases?
- What can we assume about the nature of the force at work here that lets us explain our observations?
Conclusion: A short-and-sweet summary of the major conclusion of this lab, i.e. ‘what we learned’ – from our class discussion.