Sounds From Vibrating Rubber Bands

Transcription

1 Sounds From Vibrating Rubber Bands Topic The effect of tension, thickness, and length of a string on the pitch of a tone Introduction In this experiment, you will observe some aspects of vibrating rubber bands. You will see how plucking a rubber band causes it to vibrate as it makes a musical note, and see how the speed of this vibration, and the musical note, can change. This will enable you to observe the connection between the frequency of vibration and the pitch of a note produced by it. You will then observe the different tones made by: a thick and a thin rubber band; a short and a long length of rubber band; and a tightly stretched and a slacker rubber band. Time required 20 minutes for Part A 30 minutes for Part B Materials lid from shoebox 2 pieces of cardboard (2 4 cm) transparent tape pencil 30 cm ruler three rubber bands that go around lid with the dimensions as in the table below: Thickness Length (measured double) Band A 1/ 16 in. (2 mm) 3 1/ 2 4 in. (9 10 cm) Band B 1/ 8 in. (3 mm) 7 7 1/ 2 in. (18 19 cm) Band C 1/ 8 in. (3 mm) 3 1/ 2 4 in. (9 10 cm) Safety note Be careful not to stretch the rubber bands too far because they can snap. Procedure Make sure the rubber bands are stretched evenly around the lid; if they are tighter in one place than another, your results may not be accurate. Part A: Sound and movement from rubber bands 1. With the open side of the lid facing upward, stretch bands A and B evenly around the lid about 10 cm apart (see diagram 1 on the next page).

2 1 band B band A 10 cm lid Bands A and B stretched around lid 2 lid Plucking the rubber bands 2. Pluck band A using the end of a finger as in diagram 2 above. You may need to hold the lid with your other hand so that you don t lift it off the table. Observe the movements of the band and listen to any sound made. Record these and subsequent observations in data table A below. 3. Repeat step 2 with band B. 4. Pick up the lid and place the flat side against one ear. Pluck each band and observe any differences. DATA TABLE A Plucking band A Action Observations Plucking band B Plucking the bands when lid is held against the ear

3 Part B: Factors determining the musical note made by a rubber band (i) Varying the thickness of the band 1. Fold both pieces of cardboard into a shape as in diagram 3 adjacent, and secure with transparent tape. 3 Cardboard folded into a shape 2. With the top of the lid facing upward, use the pencil and ruler to make a series of lines 1 cm apart running parallel with the longer edge of the lid. Stretch bands A and C evenly around the lid about 10 cm apart as shown in diagram 4 below. 4 band A of lid 10 cm Bands A and C stretched around the lid 5 band A 2 cm 2 cm X Y Wedges inserted between the rubber bands and the lid 3. Insert the s between the lid and the bands 2 cm from one long edge (see diagram 5 above). 4. Make a musical note from band A by pulling it with your fingernail and releasing it a few times at a point (X in diagram 5 above) half way between the and the of the lid. 5. Make a musical note from by pulling it with your fingernail and releasing it a few times at a point (Y in diagram 5 above) half way between the and the of the lid.

4 6. Record in data table B below which band produced the higher pitched tone and which the lower pitched tone. Band A is thin and is thick; write THICK or THIN in the appropriate box. (i) Different band thickness DATA TABLE B Higher pitched tone Lower pitched tone (ii) Different band length (iii) Different tension in band (ii) Varying the length of the band 1. Remove band A. Position one of the s under 3 cm from the upper, long edge of the lid as in diagram 6A below. 6A 3 cm 6B Wedge closer to top edge of lid Wedge closer to of lid 2. Make a musical note from the band by pulling it with your fingernail and releasing it a few times at a point half way between the and the lower edge of the lid. 3. Move the until it is about 9 10 cm from the of the lid (see diagram 6B above) and repeat step Record in data table B which length produced a higher pitched tone and which the lower pitched tone the shorter length of rubber band ( close to the of the lid) or the longer length of rubber band ( further away from the of the lid). Write SHORT or LONG in the appropriate box. (iii) Varying the tension of the band 1. Secure the about 3 cm from the upper, long edge of the lid with transparent tape (see diagram 7 on the next page). Stretch evenly over the lid and the. 2. Make a musical note from by pulling it with your fingernail and releasing it a few times at a point half way between the and the lower edge of the lid (point X in diagram 7 on the next page).

5 3. With one hand, increase the tension in the band by pulling it in the direction shown in diagram 7 below while keeping it in contact with the of the lid. Repeat step 2 using your other hand. 4. Record in data table B which case produced a higher pitched tone the band under tension while being pulled (step 3), or the band under less tension while not being pulled (step 2). Write TIGHT or SLACK in the appropriate book. 7 3 cm X pull edge of lid in contact with band Band under tension Analysis Part A: Sound and movement from rubber bands 1. Did band A start to move when it was pulled up and released? 2. Did band A make a sound when it was pulled up and released? 3. Did band B start to move when it was pulled up and released? 4. Did band B make a sound when it was pulled up and released? How does this compare with band A? 5. How did the sensations caused by the two bands differ when you placed the lid against your ear? 6 What do you think is the relationship between the sound produced and the movement of the rubber band? Part B: Factors determining the musical note made by a rubber band 1. Did the thick or the thin rubber band produce a higher pitched tone? 2. Did the long or short rubber band produce a higher pitched tone? 3. Did the slack or tight rubber band produce a higher pitched tone? Want to know more? Click here to view our findings.

6 Part A: Sound and movement from rubber bands 1. Band A began to vibrate quickly from side to side. It kept vibrating for a few seconds. 2. Band A made a musical note when it was pulled up and released. The sound stopped when the movement stopped. 3. Band B began to vibrate quickly when it was pulled up and released. It kept vibrating for a few seconds. 4. The note made by band B had a lower pitch than the note made by band A. It also stopped when the movement stopped. 5. When band A was pulled up and released, a higher pitched note was heard and fast (high frequency) buzzing vibrations were felt. When band B was pulled up and released, a lower pitched note was heard and slower (lower frequency) vibrations were felt. 6. The band vibrates as the musical note is heard. The musical note and the vibrations stop at the same time. The higher note made by band A is associated with higher frequency (faster) vibrations than the lower note made by band B. A band vibrating at high frequency (quickly) makes a higher pitched note than a band vibrating at lower frequency (more slowly). Part B: Factors determining the musical note made by a rubber band 1. The thinner rubber band produced a higher pitched tone than the thicker band. 2. The shorter rubber band produced a higher pitched tone than the longer band. 3. The stretched (tight) rubber band made a higher pitched tone when it was slack.