the rim of the glass by washing with dish detergent and rinsing well. Dry your hands and the stemmed glass thoroughly.2 Place the glass on a table.
3 Hold the base of the glass against the table with your hand.
4 Wet the index finger of your free hand with water and move your wet finger in one direction around the rim of the glass pressing gently.
FIG 1
What Happened?
The glass starts to “sing.” Washing your hands removes any oil that might act as a slippery lubricant. Rubbing a wet finger around the rim causes the glass to vibrate. Due to friction, your finger skips and pulls at the glass as it moves around the rim. Just in the way a tuning fork begins vibrating when struck, this irregular touching on the glass rim actually acts like tiny taps that cause the glass to begin vibrating. In turn, the air inside and outside the bowl of the glass is struck by these vibrations and begins to move back and forth in a wavelike pattern. These sound waves spread out in all directions from the vibrating glass. A musical tone can be heard. The pitch of the sound you hear is due to the natural frequency of the glass.
10 Neutral Atom
A neutral atom has no electric charge. Atoms are the building blocks of matter. Think of it as the stuff of which everything in the Universe is made. The center of an atom, called the nucleus, holds both protons, which are positively charged particles, and neutrons, which are particles with no charge. Electrons are negatively charged particles that spin around the nucleus at different distances called energy levels.
A neutral atom has an equal number of protons and electrons; thus, it has an overall net charge of zero. Much like the addition of +1 and −1 equals 0, the sum of one positive charge from one proton and one negative charge from one electron also equals zero.
The Bohr model of an atom looks much like a model of planets orbiting the Sun at different distances. Comparatively, in the Bohr model, negatively charged electrons orbit a positively charged nucleus in different energy levels. The Bohr model of an atom can be demonstrated with a paper model.
See for Yourself
Materials
blank paper
pencil
scissors
tape
What to Do
1 Fold the paper in half three times, once from top to bottom, and then from side to side, and last fold along a diagonal line so that the top folded edge meets the side fold as shown in Figure 1.FIG 1
2 Draw five curved lines on the top layer of the folded paper.
3 Cut along each of the five curved lines. Keep the three indicated sections as shown in Figure 2.FIG 2
4 Unfold the three sections; write “6p+” and “6n” in the circle, which represents the six protons and six neutrons in the nucleus of the atom.
5 In the smaller ring, draw two electrons (e−) on opposite sides, and in the largest ring, draw four electrons (e−) randomly spaced and as far apart as possible.
6 Connect the three parts by taping the string to each as shown in Figure 3. Secure the end of the string to a surface so that the atom model can hang freely.
What Happened?
This Bohr model is of the element carbon (C). The carbon atom model is neutral because it has six positively charged protons (p+) in its nucleus and six negatively charged electrons (e−) in the rings, which represent energy levels. In the Bohr model, atoms may hold up to two electrons in the first ring and up to eight electrons in the second ring. Since there are only a total of six electrons in a neutral atom of carbon, two electrons are in the first energy level and the remaining four electrons spread out in the second energy level, which is the outer ring. The electrons in the outer energy level of an atom are called valence electrons. The atom model of carbon has an overall charge of zero; thus, it is a neutral atom.
11 Electric Current
An electric current is the movement of electrons. The faster the electrons move, the more kinetic energy they have. Kinetic energy of moving electrons can be called electrical energy. The strength of the current, or flow rate, is a measurement of the number of electrons moving past a point each second and is measured in amperes (A). One ampere is equal to 6.24 quintillion (=6.24 million million million) electrons each second. You can model the flow rate of current electricity using grains of sand. Just as the flow rate of an electric current is measured in electrons per second, the flow rate of sand can be measured in the number of ounces of sand that flows per second.
See for Yourself
Materials
pencil
paper cup, 7 oz (210 mL)
masking tape
small grain sand
ruler
small bowl
timer
helper
What to Do
Note: This experiment works best on a dry day, because moist sand tends to stick together when the weather is humid.
1 Use the pencil to punch a hole in the center of the paper cup's bottom. The hole should equal the circumference of the pencil
