13 June 2010
(a) (i) Based on the results in Table 1.1, state two observations for the experiment.
1. When the length of the straw is 20cm , the weight that bends the straw is 1N
2. When the length of the straw is 5 cm, the weight that bends the straw is 4N
[ 3 marks]
(ii) State the inference which corresponds to the observation in 1(a)(i).
1. When the length is short , the strength of the straw is strong /high
2. When the length is long (P1), the strength of the straw is weak / low.
[ 3 marks]
C (i) Complete Table 1.2 based on this experiment (Dependent)
Variable | Method to handle the variable (Dependent) |
Manipulated variable The length of the straw. | By using different length of straws, that is, 20cm, 15cm, 10cm and 5cm respectively. |
Responding variable The weight that bends the straw. | By recording down the weight that bends the straws using the metal weights/ 0.5N |
Controlled variable The diameter of the straw | By fixing the diameter of the straw at 1cm |
Table 1.2
[3 marks]
(ii) Complete the table 1.3 below by classifying the materials and apparatus used in this experiment
Apparatus | Materials |
Retort stand Hook Wooden blocks 50N weights | Straw Paper/ cotton |
Table 1.3 [3 marks]
e. State a hypothesis for the experiment.
The shorter the length, the higher the strength of the straw that bends the straw.
[3 marks]
f. Based on Table 1.1, record the results of this experiment obtained in a table. Your table should include the following aspects:
- The length of the straw
- Surface area of the straw (equals the length multiply by the 3cm^{2})
- The weight that bends the straw
- The strength of the straw, using the formula: Straw’s strength = Force (Weight) divided by the straw surface area
Length (cm) | Surface area (cm^{2}) | Weight / Force (N) | Strength = F/SA (N/cm^{2}) |
20 | 60 | 1 | 0.02 |
15 | 45 | 2 | 0.04 |
10 | 30 | 3 | 0.10 |
5 | 15 | 4 | 0.27 |
[3 marks]
(ii) From the table in (f) (i) above, draw a graph of the strength of the straw against the length of the straw.
Axes – correct with the correct label and units = 1 mark
Points are correctly transferred = 1 mark
Shape of graph is correctly drawn = 1 mark. [3 marks]
g. From the graph you have drawn in (f)(ii) above, explain the relationship between the length of the straw and its strength.
When the length of the straw increases ,the strength of the straw decreases.
This is because increase in the length of the straw will increase its surface
area and thus the weight to bend it is smaller
[3 marks]
h. From the experiment, what can be deduced about the strength of the straw ?
The strength of the straw is the maximum weight it can take before it bends , when the weight is hung from its middle portion, the strength of the straw is affected by its length.
[3 marks]
i. If a same type of straw, is clamped on the same retort stands with length 20cm with the thicker wall, between the wooden blocks, predict the strength of the straw.
The strength of the rod will be stronger than 0.02 N/cm^{2}.
This is because the straw has the same diameter and length but it has thicker wall, giving it more strength , so increasing its strength