1. antinodes (max. vibration)
Review
Longitudinal Standing Waves
nodes (no vibration)
antinodes (max. vibration)

2. 2018 class effort
Tf-Ti= s
Tube length L = 2.42 m
V sound =325 m/s
Main error in L value?
Quick activity: in groups of 4, determine the speed of sound can you do better?

3. G) Use Vernier Microphones (& logger pro) to determine the speed of sound for a long PVC tube with:
one with a closed end (reflected wave)
both pipe ends open - see pictures below for closed end.
Which method is more accurate?
Explain in detail the Physics relating to why there is a reflected wave at an open end! See

4. Wind instruments create sound through standing waves in a column of air.

6. vibrating air molecules
When air is blown over a bottle, it creates a standing longitudinal (sound) wave
Use rugby balls (or lemons) to visualize the standing wave shape being formed.
The rugby balls are describing vibrating or moving air molecules.
The molecules of air are less constrained where the bottle (or tube) is open to the surroundings, so an antinodes (locations of maximum displacement) occurs at open ends. A node point (zero displacement) occurs at closed ends.
open end: antinode
(rarefaction)
vibrating air molecules
closed end: node
(compression)

7. Strike the end of the PVC tube with your finger, as shown in Figure 1
Strike the end of the PVC tube with your finger, as shown in Figure 1. If done correctly, a sharp hollow sound will be produced. Now strike the tube against your palm, as shown in Figure 2. How does the tone of this sound compare to that produced earlier?
Enquiry…
Which ‘strike’ has
a higher pitch?
Determine the pitch using the Vernier microphone
and logger pro software…
Later you will determine your answer using
or ?

9. Air pressure Nodes verse air displacement Nodes…
Air pressure Nodes verse air displacement Nodes…??? This is complex but worth understanding!
Can you see lemons or rugby balls

10. Air pressure Nodes verse air displacement Nodes…
Air pressure Nodes verse air displacement Nodes…??? This is complex but worth understanding!
Can you see lemons or rugby balls

11. F) Solve the mystery of the flame pipe  
Confirm whether flame peaks are a pressure node or an anti-node? (supervision required for this activity)
Possible enquiry aspects: does the pipe represent two closed ends? Effect of warming pipe temperatures on speed of sound and harmonics generated...
Wave & Sound unit - Enquiry Investigation lab info: Option F

12. T) Make a Kundt's tube
Kundt's demonstration, first described in 1866, gives a visual record of the nodes and antinodes of a standing wave set up in a tube. It can be used to determine the speed of sound within the tube, but here you are only asked to show standing wave behaviour.
Mr Anderson & Mr Tonks tried to make this but failed… students turn?
See
And video -
Or without a speaker see
Wave & Sound unit - Enquiry Investigation lab info: Option T

13. Stable high gas pressure point is a Node…?

14. Lemons
This one …

15. Displacement and pressure variation are complementary pictures
Displacement and pressure variation are complementary pictures.  When particles are free to move you have a displacement anti-node, like the open end of a tube, and the variation in pressure is zero, hence a pressure node.  When particles are constrained by a wall you have a displacement node and the pressure variation at that wall is maximized hence a pressure anti-node.
At the right side where the tube end is closed, you can see that particles don't move through the end (there's a wall there). So, all of the particles that hit bounce back elastically (ideally) experiencing maximum change in velocity and therefore, causing maximum pressure while they are bouncing. After they've bounced there's a momentary lull in bounces and you get a minimum of pressure. So, the fact that the particles CANNOT move through the closed end (a displacement node) means you must get a pressure maximum variation (antinode). It's less obvious or intuitive other than by analogy that where there's an opening there is a displacement antinode (maximum in and out) there has to be a pressure node (no change).
Web based Physics teacher discussion board comments…

16. Don’t stress – can you cope with this MCQ?

17. You can also ring a tuning fork over a bottle or tube, and if it creates wavelengths of just the right length, you’ll get a standing wave (loud sound).

18. ? How is a sound wave reflected back in an open end pipe?
Consider a low pressure region travelling along the tube towards the open end. The air outside is at atmospheric pressure, so when the low pressure region hits the end of the tube air from the atmosphere rushes in and creates a compression wave heading back down the tube. The opposite happens when a high pressure region hits the end of the tube.
Basically just assume that sound waves are reflected from a closed end AND from an open end…

19. CLOSED PIPE
Just like we did for strings, we can also derive a formula to calculate……
n = 1,3,5,…
The Harmonic Frequencies for a tube open at one end
speed of sound
odd harmonics only

20. Trombone (closed pipe?)
What would have to happen to play a lower note on a trombone without changing the number of harmonics?
Increase the length
Decrease the length
Increase the length & blow faster
Increase the length & blow slower
Decrease the length & blow slower

21. A closed pipe has a fundamental frequency of 150 Hz
A closed pipe has a fundamental frequency of 150 Hz. Which of the following cannot be heard on this pipe?
A) 300 Hz
B) 450 Hz
C) 750 Hz
D) 1050 Hz
E) all of the above are possible.

24. Saxophone is closed so: L= 1/4 λ
A saxophone (assume has a closed end) plays a tune in the key of B-flat. The saxophone has a third harmonic frequency of Hz when the speed of sound in air is 331 m/s. What is the length of the pipe that makes up the saxophone?
f' = f3/n
= 466.2/3
= Hz
Saxophone is closed so: L= 1/4 λ
n = 3
f3 = Hz
v = 331 m/s
= 0.53 m

25. A pipe that is closed on one end has a seventh harmonic frequency of Hz. If the pipe is 1.53 m long, what is the speed of the waves in the pipe?
n = 7
f7 = Hz
L = 1.53 m
L= 7/4 λ and λ = 4/7 L
= m/s

26. Standing waves can also occur in a tube that is open at both ends
OPEN PIPE
Standing waves can also occur in a tube that is open at both ends

27. Harmonic Frequencies for a tube open at both ends
OPEN PIPE
A tube open at both ends has displacement antinodes, at the ends.
Harmonic Frequencies for a tube open at both ends
n = 1,2,3,4,…

28. Flute (open ended pipe)
Starting with all the valves closed, what happens to the pitch as I open the valves in order? Why?
Pitch increases b/c the length is increasing
Pitch increases b/c the length is decreasing
Pitch decreases b/c the length is increasing
Pitch decreases b/c the length is decreasing
Pitch increases b/c the harmonics are increasing

29. An open pipe has a fundamental frequency of 140 Hz
An open pipe has a fundamental frequency of 140 Hz. Which of the following is NOT a harmonic which can be played on this pipe?
A) 280 Hz
B) 420 Hz
C) 560 Hz
D) 70 Hz
E) 1400 Hz

30. Hard!

31. An organ pipe that is open at both ends has a fundamental frequency of Hz when the speed of sound in air is 331 m/s. What is the length of this pipe?
f' = 370 Hz
v = 331 m/s
L= 1/2 λ
= m

32. L= 1/2 λ and λ = 2L v = λ f =2 L f = 2(1.32)(125) = 330 m/s
A pipe that is open at both ends has a fundamental frequency of 125 Hz. If the pipe is 1.32 m long, what is the speed of the waves in the pipe?
L= 1/2 λ and λ = 2L
v = λ f
=2 L f
= 2(1.32)(125)
= 330 m/s
f' = 125 Hz
L = 1.32 m

35. Use tuning forks or cell phone apps to generate forced sound frequencies?
Use your ears or Vernier microphones to determine resonance length

36. End correction factor????
A clever question this …

37. Open-End vs Closed-End Tube
If both an open-ended instrument and a closed-end instrument are playing the same note at the same harmonic, which instrument has a longer tube?
Open-end
Closed-end
The same
Can’t be determined