5 Stick your index fingers in your ears and lean forward so the hanging spoon dangles freely. Check to make sure the string is not touching any object.
6 Again, ask your helper to tap the spoon as before. Compare the two sounds.
What Happened?
Everything that vibrates sends out sound waves through the air in all directions. The frequency or pitch of the sound was the same each time the spoon was tapped. But, the amplitude, or loudness, of the sound was greater with your fingers and the string pressed into your ears. This is because when traveling through air, the sound waves move slower than when they travel through a solid. Thus, more sound waves reached your ears when they traveled up the string to your ears. Also, the string provided a direct route for the sound from the vibrating spoon to your ears.
8 The Effect of Mass on Sound
Mass is a measure of the amount of matter in an object. For example, some drinking glasses are thicker than others, thus they are more massive. In reference to sound, the more massive a vibrating object, the lower the frequency, and hence the pitch. The reverse is true if the mass decreases with a result of a higher frequency and higher pitch.
In this activity, water will be added to glasses to change their mass. Tapping on a glass with water will produce a sound with a certain frequency. It will be seen that increasing the mass of a glass and then tapping on it will produce a sound with a lower frequency. Altering the amount of water in the glass can produce different musical notes.
See for Yourself
Materials
6 drinking glasses of equal size and shape (the thinner the glass walls, the better)
water
food coloring
pencil
What to Do
1 Pour different amounts of water in five of the glasses. Leave one glass empty.
2 Using food coloring, make the water in each glass a different color. Note: The coloring doesn't change the sound that will be produced. It merely helps to associate each glass with the sound it produces.
3 Gently tap each glass with the wooden end of a pencil.
4 Compare the sounds made by each glass with water to the sound produced by the empty glass. Determine which produces the highest and the lowest frequency.
FIG 1
An experimental challenge is to alter the amount of water in each glass to produce the notes to play a simple song.
What Happened?
The sound produced by tapping each glass was different depending on the amount of water it contained. The sound heard also depended on the sound produced by the glass; thus, an empty glass was used that vibrated the fastest when tapped, so it had the highest frequency and the note was high. A glass with water in it vibrated slower when tapped because the glass and water together had a greater mass. The greater the mass, the slower the vibrations of the glass when tapped. Slower vibrations mean a lower frequency of sound waves. The high and low musical notes produced are related to frequency. High notes are produced by high frequencies and low notes by low frequencies. Adjusting the level of water in a glass can result in notes that go up or down the musical scale.
9 Natural Frequency
Natural frequency is the frequency at which a material vibrates when hit, plucked, strummed, or somehow set into motion. When a tuning fork is struck, it vibrates at a specific frequency: its natural frequency. As a tuning fork vibrates, it causes the air around itself to vibrate, which produces the sound waves you hear. A simple motion, such as rubbing the rim of a glass, can cause it to vibrate at its natural frequency and produce sound.
See for Yourself
Materials
stemmed glass (this will work best if the glass is thin)
dish detergent
small bowl of water
What to Do
1 Remove excess oil from your hands and clean 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