Practical Activity for 14-16
Students make their own springs and use them for investigations involving simple graph construction.
Apparatus and Materials
- For each student group
- Bare copper wire, 26 SWG (0.45 mm), 80-90 cm for each student in group
- Clamp stand and boss
- G-clamp or other method of fixing stand to bench
- Flat-headed nail, large
- Mass hanger with slotted masses (10 g)
- Sticky-backed tape, e.g. ticker-tape
- Eye protection for each student
Health & Safety and Technical Notes
Students should clamp their stand to the bench to prevent it from toppling.
Students must wear eye protection. Eyes may be at the same level as clamp and the nail.
Use new copper wire. Old wire is often uneven in its hardness as working of copper wire hardens it. Also, twisted wire will produce uneven springs. You can use the wire afterwards for chemical and electrical work.
- Make a spiral spring by winding the copper wire round and round a pencil. Do this by turning the pencil (to avoid twists), for 25-30 turns. Make a twisted loop at each end.
- Fix the nail horizontally, with its point in the boss on the stand. Hang the spring from the nail.
- Cut a piece of tape, the same length as the hanging spring. Write number 0 on the tape. That is the number of masses that you have hanging from the spring.
- Attach the mass hanger to the lower loop of the spring. Cut a new piece of tape, the same length as the stretched spring. Write number 1 on the tape, because there is one 10-gram mass hanging from the spring (the mass of the hanger).
- Add a mass to the hanger. Cut another piece of tape, the same length as the stretched spring. There are now two 10-gram masses, so write number 2 on the tape.
- Add more masses, one at a time. Each time, cut a new piece of tape and write the number on it.
- Draw a horizontal line close to the bottom of a sheet of paper. Paste your pieces of tape side by side. Start with the shortest piece, which has number 0. The bottom ends of each piece of tape should touch the horizontal line. You have made a ‘graph’ of the length of the spring and the number of masses.
- Write a conclusion for this investigation. You should explain how the number of masses affects the stretch of the spring. Your paper-tape graph should help you to do this.
- This activity is intended for students who are developing familiarity and confidence with creation and interpretation of simple graphs. A ruler could also be used to measure the length of the spring if students are able to translate measurements into a graph.
- It is important that each student should make a spring and does not have to passively observe others doing so. The measurements can be done with just one spring for each student. Alternatively, springs could be made from different materials and different wire gauges. In fact anything that stretches will give a set of graphs to discuss.
- Allow students to ‘ruin’ their springs by over-stretching them.
- Encourage students to find answers to questions such as:
- "Does the spring stretch regularly?"
- "What happens if too large a load is attached?"
- "Does a spring always ‘spring’ back to its original shape?"
- "Can you put a stretched spring back into its original shape?"
- For able students, you could point out that the number of masses is the input variable, or independent variable, of this investigation, and that the length of the spring is the output variable or dependent variable. Also, tell students that the usual convention is to plot the input (independent) variable on the x axis of a graph and the output (dependent) variable on the y axis. You could explain that they, as investigators, have complete control of the input (independent) variable but can only observe and measure the output (dependent) variable.
- By cutting off the initial spring’s length from each tape, the graph becomes one of extension against number of masses. Ask students to draw a horizontal line across the graphs at the original length, and then cut along this line. How Science Works Extension: The results of this extension can be summarized as Hooke’s law. This experiment thus gives an opportunity to discuss what is meant by a ‘law’ in physics, and the etiquette of scientific publishing.
- Robert Hooke (1635-1703) was a few years older than Newton. He studied springs for a specific practical reason: he wanted to devise an improved spring-driven watch. Hence it was important to understand the behaviour of springs. He studied both linear and spiral springs.
- It was important to Hooke to be able to claim priority in the discovery of his law, but at the same time he did not want his competitors to benefit from his findings. He therefore published a summary of his findings in the form of an anagram: “ceiiinosssttuv”
- Later, he revealed that it was an anagram of a sentence in Latin. Decoded, it said: “Ut tensio, sic vis.”
- In English, this is: “As the extension increases, so does the force.”
- In other words, the extension is proportional to the force producing it. Today, it would be regarded as unacceptable for a scientist to keep results secret in this way. Results should be published in a form that allows others to repeat them, and to take the work further if they so desire.
This experiment was safety-checked in September 2004.