:Banjo Boxes
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Approach:  One to one Level: Year 4 and year 8
Focus: Sound generation and transmission 
Resources: “Banjo box”, coloured and brown rubber bands, 2 pieces of dowel, picture
636KB

Questions/instructions:

In this activity we’ll be thinking about sounds and how they’re made. First I’m going to make a simple banjo.

Place the box, two rubber bands and two pieces of dowling on the table.
Teacher makes banjo box, telling the student.....
These are the materials I’ll use to make a simple banjo. I put the rubber bands around the box lengthwise. I make sure the two rubber bands are not touching each other. Then I put the pieces of wood under the rubber bands near the ends of the box.
  
Once the banjo has been made give it to the student.

Now I would like you to pluck each of the rubber bands and listen carefully to the sounds the two rubber bands make.

Allow time for student to experiment.

% responses
2003 ('99)
y4
y8
1. What can you tell me about the sounds?

Prompt: What is different about them?
coloured band makes higher sound/pitch
54 (50)
72 (78)
If the student didn’t notice that the coloured rubber band made a higher sound than the brown rubber band, demonstrate and say,
“The coloured rubber band makes a higher sound than the brown one”.
2. Try to explain why the coloured rubber band made a higher sound.


 Explanation:
[coloured band thinner/lighter;
coloured band stretched more tightly]
included both ideas
9 (9)
14 (9)
included thickness/mass
75 (73)
76 (77)
included tension/tightness
4 (4)
4 (6)
3. Try to explain how the sound gets from the rubber band to our ears.
band makes vibrations in air which travel to ears and are heard
14 (17)
24 (22)
vaguely mentioned air vibrations
25 (32)
38 (50)
4. What do you think would happen to the rubber band sounds if we took the pieces of wood out?

Prompt: In what way might it sound different?
sound will not ring out properly,
or will stop quickly
41 (37)
68 (57)
Let’s take out the pieces of wood and see what happens.

Remove pieces of wood.
5. What do you notice about the sounds the rubber bands make now?
sound does not ring out properly
or stops quickly
18 (10)
38 (45)
difference in pitch (lower)
22 (20)
20 (17)
6. Try to explain why the sounds are different when the pieces of wood are taken out.
stops bands from vibrating properly
34 (29)
53 (68)
Show picture of stringed instruments.

This picture shows some stringed instruments.

Notice that they all have a hole.
7. Why do you think these instruments have holes in them?
open cavity allows sound to resonate and amplifies sound
15 (19)
35 (37)
lets sound in/make sound louder
31 (34)
39 (40)
 
Total score:



11–13
4 (5)
16 (20)
8–10
19 (18)
37 (40)
5–7
37 (39)
34 (29)
2–4
36 (33)
13 (9)
0–1
4 (5)
0 (2)
Commentary
Year 8 students, on average, performed substantially better on all task components. There was very little change in performance between 1999 and 2003.
 
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