P6 Forces Topic
Elastic Spring Force – Comparing Different Springs
This science revision note aims to help your child:
– compare the different extensions of the springs
– Understand the elastic limit of the spring.
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Ashraf had two springs (A and B) and some weights. He hung weights of different masses on each of the springs and measured the length of the spring at each mass. His results are shown in the graph below.
Based on the graph, which of the following statements can Ashraf conclude from his experiment?
1) The elastic limit of Spring A is 35cm.
2) The original length of Spring B is 20cm.
3) When the weight is 50g, the extension of Spring A and B is the same.
4) When the 40g load is added to the springs, Spring A stretches more than Spring B.
Let’s go through each option to determine which is correct.
“The elastic limit of Spring A is 35cm.”
Based on this question, the elastic limit means the maximum extent to which a spring may be stretched without permanent alteration of the size or shape of the spring.
If the spring is stretched beyond its elastic limit, the spring will be permanently altered and does not return back to its original length.
How to show that in a line graph?
You just have to know this (not the most accurate description but good enough for primary-level students): When the final length of the spring remains constant (despite adding more weights to it), that means the spring is stretched beyond its elastic limit.
Although 35cm is the maximum length of Spring A in the graph above, the graph does not show any constant line.
It is unclear whether adding weights above 100g will result in the length of Spring A remaining at 35cm or if it will continue to increase the length of Spring A.
Hence, it is unclear what the elastic limit of Spring A is, and Ashraf cannot conclude this statement.
This statement is not the correct answer.
“The original length of Spring B is 20cm.”
The original length of each spring is the length of the spring when the mass of the weight is 0g, meaning there is no weight hung from the spring. Hence, the original length of Spring B is 10cm.
Recall this information about the line graph (not the most accurate description but good enough for primary-level students): When the final length of the spring remains constant (despite adding more weights to it), that means the spring is stretched beyond its elastic limit.
Looking at the graph in the question above, the length of Spring B stays the same (20cm) is the elastic limit of Spring B, which is the maximum length Spring B can be stretched without permanently altering the spring.
Hence, this statement is incorrect.
“When the weight is 50g, the extension of Spring A and B is the same.”
When the weight is 50g, both Spring A and Spring B are 20cm in length. However, we have to take note that the springs started out at different original lengths, meaning they have extended different lengths when the weight of 50g is added.
Spring A is originally 5cm, so it extended by 15cm.
Spring B is originally 10cm, so it extended by 10cm. Hence, although both springs reach 20cm when 50g of weight is added, their extensions are different.
This statement is incorrect.
“When the 40g load is added to the springs, Spring A stretches more than Spring B.”
When 40g of weight is added, Spring A stretches by (around) 17cm, while Spring B stretches by (around) 8cm. Spring A does indeed stretch more than Spring B.
This statement is correct!
FINALLY, choose the correct answer.
The answer is 4.
Note: You need to practise similar questions to visualise how to compare different springs.
Once you’ve got enough training, you can choose the correct answer much more quickly! 🙂
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Click here a more challenging question on springs >>> https://scienceshifu.com/elastic-spring-graphs/
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