Bolt Sounds

Introduction

Drop bolts onto stone and listen to them ring.

Material

• Bolts of different lengths (minimum 10 cm long) and different diameters.
• nuts to fit the bolts
• a brick or other stone surface
• Soft material to catch the bolts

Assembly

Mount the stone surface on the edge of a table top so the top surface makes a 45 degree angle with the ground.

Place the soft material to catch bolts bouncing off the stone.(The soft material will dampen the sound of the bolts when they hit the floor.)

To Do and Notice

1.) Drop the bolts onto the middle of the stone surface near the bottom edge so that they bounce outward and land in the soft material. To make the cleanest bounce angle the blot so that it is perpendicular to the brick's top surface when dropped, this will keep the bolt from rotating and hitting the brick a second time.

2.) Drop short bolts and long bolts of the same material and diameter. Notice that the short bolts have a higher pitch than the long ones.

3.) Screw a nut onto a bolt and drop it again, notice that the sound is damped to almost nothing.

4.) Screw two nuts onto a bolt and tighten them together. Drop the bolt and notice that it rings again with a lower frequency.

5.) Drop two bolts of the same length and made of the same material but with different diameters and notice that the larger diameter bolt has a higher frequency.

6.) Arrange a handful of bolts in a row and drop them one at a time to play music.

What's Going On?

1.) The collision of the bolt and the stone sets the bolt into vibration. Resonant frequencies of the bolt ring the longest. The vibrations are longitudinal and transverse. The longitudinal vibrations are ultrasonic. We hear the transverse vibrations. the length, diameter and material of the bolt determine it's resonant frequency.

2.) Longer bolts of the same diameter and material vibrate with lower frequencies.

3.) The rattling vibration of the loose nut turn the organized vibrations of sound into the disorganized motions of heat.

4.) Two nuts turned tightly together do not rattle and do not turn sound into heat. They do lower the frequency of the bolt.

5.) The audible sounds made by the bolts are from transverse vibrations. Bolts with larger diameters are harder to bend and so have higher resonant frequencies all else being the same.

Going Further

Resources

 Scientific Explorations with Paul Doherty © 2009 25 June2009