Sticky Tape Lab

The Set-up

We Left These Hanging

Possible Results REPEL Top Bottom Foil Paper ATTRACT NEUTRAL Plastic (Other)

Possible Results 2

What’s Going On? To explain the source of these charges, we need to expand our model of the atom to have some internal structure. We will assume that each atom contains both positive and negative charges that normally cancel each other.

What’s Going On? J. J. Thomson proposed that in solids, only the negative charges are free to move, and that these charges are much smaller than an atom and carry only a negligible fraction of its mass. We will use the Thomson model of the atom – a massive positive core associated with a small number of mobile, negatively charged particles we call “electrons”

What’s Going On? A visual representation of this model is the “plum pudding” model. I’ll reference this as chocolate chip cookie dough. The positive cores are represented by bowls of “dough”, which attract the negative electrons represented by chocolate chips. The attraction of the chips to some bowls is stronger than to others, and they can move from one bowl to another because of such differences in attraction. However, since “chips” also repel one another, you cannot cram too many “chips” into the same bowl of dough.

Let’s Apply the CCCD Model to our Sticky Tape Lab CCCD? Chocolate Chip Cookie Dough

Tape: Before adhesion Neutral atoms (+ = -) dot = negative electron

Tape: In contact negative can move (positive can’t) top(+) bottom (-)

Tape: Separated top(+) bottom (-) Why is the top now positive and bottom piece now negative? Think about the comparison of positive and new amount of negative charge.

When two objects of different substances come into contact, some electrons move from one substance to the other (some chips creep from one set of bowls into the other). If the objects are then quickly separated, an excess of electrons remains in one object (creating overall negative charge), counterbalanced by a deficiency of electrons in the other (overall positive) I.e.: one set of bowls is now “chip rich”, while the other is “chip deficient”.

This microscopic imbalance of charges translates to an overall macroscopic charge on the object. The T tape becomes positively charged because electrons are transferred to the B tape. The overall number of electrons does not change, just their distribution on the tapes.

Neutral Foil (how do + and – compare?)

T-tape approaches foil Electrons become polarized and move toward the Top Tape (or some other positive object). The macroscopic effect is an attraction of objects

How would B-tape approaching foil look? See the Balloon and Static Electricity simulation on the class site: http://sciencewithhoffman.weebly.com/unit-6-particles-w-internal-structure.html for another look at the polarization of materials causing attraction/repulsion

The attraction between both T and B tapes and the aluminum foil is greater than that observed with the paper. In metals, electrons can be compelled to move from one core to another by the application of an external electric field. The same electric field does not result in movement of electrons in non-metals. We conclude that the attraction of the cores to the electrons is weaker in metals.

T-tape approaches Paper The effect of polarization in an insulator is less pronounced because the electrons are not so free to move about (each chip stays in its own bowl).