Pages 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 11844 result(s) returned

Acknowledgements

Except for third party materials and otherwise stated (see terms and conditions), this content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 Licence

Grateful acknowledgement is made to the following sources for permission to reproduce materia
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

6 Radiation

All the primary vibrators we discussed in the previous section can to some extent communicate vibrations to the surrounding air and hence radiate sound. However, some radiate sound better than others. Air columns, for example, radiate sound quite well. Even though only around 1% of the energy possessed by a vibrating air column is radiated away, this is enough to produce a clearly audible note.

Similarly, circular membranes and circular plates are also good sound radiators. They have a
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

5.14 Response and damping

You have learned so far in this chapter that when a musician plays an instrument, they force the primary vibrator to vibrate. If the primary vibrator is driven at one of its resonance frequencies, the normal mode of vibration corresponding to that resonance frequency will be excited. Now, in practice it is also true to say that even if the primary vibrator is driven at a frequency close to the resonance frequency, the normal mode will still be excited, but just to a lesser degree. In other wo
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

5.13 Other primary vibrators

You saw in the previous two sections that stringed instruments and wind instruments possess primary vibrators that have harmonically related natural frequencies. As a result, these two classes of instruments produce notes that have a well-defined sense of pitch.

In this section, I want to briefly introduce you to some primary vibrators that don't have harmonically related natural frequencies. Specifically we shall take a look at a rectangular bar, a circular membrane and a circular plat
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

5.12 Vibrating air column: pitches of notes produced by wind instruments

In a wind instrument, the air column is the primary vibrator. To excite the air column, a musician either blows across it (e.g. flute) or blows down it via a mouthpiece (e.g. trumpet) or reed (e.g. oboe). This supplies energy, which starts the air column vibrating. The air column isn't just forced to vibrate in one single mode; as with the string, it vibrates in a combination of several modes.

To a good approximation, the air column of a flute is cylindrical with two open ends and, as a
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

5.11 Vibrating air column: standing waves in a conical tube

The third configuration of air column that we shall consider is that enclosed by a conical tube. Figure 17 shows the normal modes of vibration for a conical tube plotted in terms of pressure. As you would expect, there is a pressure antinode at the closed tip of the cone and a pressure node at the open en
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

5.10 Vibrating air column: end effects

In the previous two sections on standing waves in cylindrical tubes, we assumed that at an open end there must be a pressure node. In fact, the pressure node (and the corresponding displacement antinode) actually lies a small distance outside the tube. The effect is that the air column behaves as though it were a little longer than it really is by an amount called the end correction. Because of this end correction, the resonance frequencies will be a little lower than originally expect
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

5.9 Vibrating air column: standing waves in a cylindrical tube closed at one end

We'll now turn our attention to the setting up of standing waves in an air column contained within a cylindrical tube that is open at one end but closed at the other. Straight away we can say that the closed end must be a displacement node since the air molecules can't move at this boundary. That means it must be a pressure antinode. The open end, as we saw previously, will be a displacement antinode (that is, a pressure node).

Now, you may recall that the distance between a node and a
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

5.2 Vibrating string: speed of wave propagation

If standing waves are set up when two travelling waves moving in opposite directions interact, then how are standing waves set up on a string and why are they set up only at certain frequencies?

To help answer these questions, I want you first to imagine a length of string that is fixed at one end and held in someone's hand at the other. Suppose the person holding the string flicks their end of the string in such a way that an upward pulse is sent along the string.

As the pulse pa
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

2 What is a musical instrument?

Figure 1

3.5.4 Fungi

Fungi (e.g. species such as Penicillium which are used for manufacture of antibiotics, and yeast) are generally unicellular non-photosynthetic organisms which can tolerate acid conditions. They are capable of degrading highly complex organic compounds. They utilise much the same food sources as bacteria but they require less nitrogen since their protein content is lower. Fungi play an important role in sewage treatment.

In polluted water, particularly near to a se
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

3.5.3 Protozoa

Protozoa are microscopic single cell animals. They utilise solid substances and bacteria as a food source. They can only function aerobically, and in a stream which contains little organic degradable matter they can become a predominant microbial type. They play an important part in sewage treatment where they remove free-swimming bacteria and help to produce a clear effluent.

In an aquatic environment, there are three main types of protozoa:

    Author(s): The Open University

    License information
    Related content

    Copyright © 2016 The Open University

3.5.2 Bacteria

Bacteria are organisms of special significance to the study of clean and polluted waters because they break down organic matter. While most of them are not harmful to humans, some bacteria (e.g. Clostridium) are pathogenic. Most bacteria are retained on a filter of pore size 0.45 μm and all bacteria are trapped on a filter of 0.22 μm. They are important in sewage treatment, and in solid waste disposal. They are extremely abundant in almost all parts of the aquatic env
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

3.5.1 Algae

Algae are photosynthetic organisms that are generally aquatic; they are primary producers. Many freshwater algae are of microscopic size, but when amassed can be seen as a green, brown or blue-green scum. Blue-green algae are capable of producing toxins and these have caused the death of wild animals, farm livestock and domestic pets which have consumed the contaminated water. The toxins can produce a painful rash on human skin. The extract below shows what happened off the west coast
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

3.3 The experiential model of learning

The main proponent of this approach to learning, David Kolb, put forward a theory which he intended to be sufficiently general to account for all forms of learning (Kolb, 1984). He argued that there are four distinctive kinds of knowledge and that each is associated with a distinctive kind of learning. The four kinds of learning are:

  • concrete experiencing

  • reflective observation

  • abstract analysis

  • activ
    Author(s): The Open University

    License information
    Related content

    Copyright © 2016 The Open University

1.6 Building on strengths

Activity 1

A self-review exercise for your learning file

The aim of this activity is to encourage you to take a problem-solving approach to your own learning, and to be proactive. The first part asks you to refle
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

1.2 Learning beyond course study

Learning how to learn has become an important goal in higher education. There is a national context in which an emphasis on ability to learn has come to prominence. It is now widely asserted that an ability to learn is as important an outcome of university study as knowledge of a discipline. This is a view put forward strongly by employers, for example, who have an interest in the employability of graduates and the skills they bring into the work place. It is a view which has been reiterated
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

3.3.4 Examining the parts

Brittle fractures were discovered quickly in the mass of debris hauled from the river. Such samples became the focus of increasing effort as time went by, simply because they were unexpected. So the possible failure mechanisms were immediately narrowed down when brittle fractures of critical components started to emerge from the river.

Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

3.3.2 Planning the investigation

A plan was needed to determine the chain of events leading up to and during the collapse. That sequence would necessarily depend on which parts had broken first, and a fault tree would enable a plan of action in isolating the cause (or causes) of the disaster. Such a systematic approach is known as fault-tree analysis or FTA, and is part of the armoury of methods used by accident investigators. With large-scale and devastating accidents, all possibilities, however remote, need evaluation in t
Author(s): The Open University

License information
Related content

Copyright © 2016 The Open University

The Graeco-Roman city of Paestum
What can archaeological remains tell us about early cities and the people who lived in them? This album examines the important remains of one city, Poseidonia in Italy, founded towards the end of the 7th century BCE by colonists from the Greek city of Sybaris. Although only twenty-five per cent of the site has been excavated to date, much of its history and culture can be traced through its buildings, inscriptions, and decoration. After it became a colony of Rome in 273 BCE, it became known a
Author(s): The OpenLearn team

License information
Related content

Except for third party materials and otherwise stated (see http://www.open.ac.uk/conditions terms and conditions), this content is made available under a http://creativecommons.org/licenses/by-nc-sa/2

Pages 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593