have a look at this study and suggest one more limitation(which is most significant):
Experiment procedure
Secure the spring vertically on a stand and clamp. Attach a ruler next to the spring as a reference scale.
Measure the spring's initial length using the ruler and vernier caliper. Record the data.
Gradually heat the spring with a heat gun while controlling its temperature at multiple points (top, middle, bottom) , use an infrared thermometer to measure temperature and ensure uniform heating.
Attach a 100g mass to the heated spring, allow it to reach a new equilibrium, then measure the final displacement using both the ruler and vernier caliper. Record the data.
Remove the weight and allow the spring to return to its original position.
Repeat steps 3-5 at different temperatures, recording the displacement for each temperature.


Safety precautions

Safety measure
Justification
Heat Protection
Wear gloves during the experiment because of exposure to high temperatures in order to prevent burns.
Protective Equipment
Wear safety goggles to protect eyes from potential harm or heat when adjusting or observing the spring.
Clear Workspace
The workspace will be kept tidy and without flammable objects such as paper to minimise the risk of accidents, especially around heating equipment.
Temperature of spring
Touch the spring and other apparatus that were heated after confirming that all apparatus are completely cooled down in order to prevent scalding.


Fair test measurements
Consistent Measurement Techniques: The exact same method and tools used for all trials of measurements will be the same to maintain the accuracy and reliability of measurements.
Digital Equipment: Digital infrared thermometer and digital vernier calliper will be used in order to eliminate human error during measurements to ensure precision in temperature and displacement measurements.
Temperature range: Since the change in temperature is too fast to measure the exact same temperature in each trial, to solve this, a range of temperature for each ten temperature units will be set to collect data.
Multiple trials: At each temperature range, 3 trials will be done to ensure consistent results and identify any error and outlier data points.

Raw data and uncertainties
Raw data and uncertainties
The temperature of the spring is measured by the digital infrared thermometer which is taking 1 decimal place and the unit is degree Celsius, so there will be a systematic error of ±0.05°C of the independent variable. The length of the spring is measured by the digital vernier calliper which is taking 1 decimal place and the unit is millimetre, so there will be a ±0.05mm systematic error of the dependent variable.

The initial length of the spring is measured 110.3mm in all three trials.
Final length of the spring:

Table 1. Experimental data of the total length of the spring and temperature of the spring

Calculation process
Approach
To approach my targeted variable, which is the spring constant, I applied the Hooke’s law：
mg= -kx
To find out the spring constant k, the constant mass of 100g, the gravitational acceleration g = 9.81ms-2 , and the difference of displacement measured can be used to calculate.

Calculation sample
Using the first data point in the first trial, refer to equation ①,
mg= -kx
Taking upward as positive,
0.19.81= -k( -(130.8-110.3))
k=0.0481 Nm−1(correct to 3 sig. fig.)
The error will be:
0.05130.8100%=0.0382%


Analysis
Processed data
Using the previous calculation method, the process data can be shown (The spring constant in the table has been rounded to 3 significant figures):

Table 2. Processed data table

Graphical representation of processed data

Figure 3. Graphical representation of processed data
Since the error of spring constant is about 0.03% and the error of temperature is 0.05°C, these errors are too small to be observed, thus causing that although the error bar is plotted on the graph, it is way too small so that there seems that there is no error bar on the graph, so as the maximum and minimum trendline.

Trend
From the graph, it can be analysed that there is a negative linear relationship between temperature of the spring and the spring constant. This shows that when the temperature increases, the spring constant decreases. This suggests that the material properties of the spring are affected by temperature. This result supports my hypothesis thus the null hypothesis can be rejected.

The trend of decrease in the spring constant with rising temperature suggests that the spring might become less stiff and tough as it gets hotter. 

Trendline
The equation of the line of best fit is given by y= −0.0003x+0.0542. This indicates that for each degree Celsius increase in temperature, the spring constant decreases by 0.0003 N/m.

Correlation
The R2 value is 0.9495, suggesting that there is a strong linear correlation between the independent and dependent variables which are temperature and the spring constant respectively. This high value indicates that the model explains approximately 95% of the change in the data.

Conclusion and analysis
The investigation into the effect of temperature on the spring constant of 304 stainless steel springs shows the significant relationship between the environmental factor of heat and the properties of materials. This study was inspired by an everyday observation involving a ball pen which uses a stainless steel spring in it. This observation leads me to make more in depth  investigations related to the topic of thermal physics and spring forces. 

The aim of the research was to investigate the relationship between temperature of a spring and its spring constant. During the experiment, the aim is found, where the relation between these 2 variables is found. Additionally, the observations in real life can also be explained by the findings of this experiment.

The results showed a negative linear relationship between temperature and the spring constant. This relationship can be applied in real life as they can explain the influence of the stiffness of springs in machines that are exposed to temperature fluctuations(Minor). 

To apply the study findings in real life, this investigation can show the importance of considering environmental factors while designing machines, especially those that include springs. From the study it can be known that the spring’s mechanism changes under different temperatures. After understanding this mechanism, it can help to explain phenomena caused by this effect, to help to develop a solution to consistent performance of springs across different environmental conditions. 

Overall, investigating this relationship helps to explain the effects of temperature on materials used in everyday objects and thus explaining the phenomena that can be observed in real life.

Reflections
Strength and limitations
Strengths
Real-World Relevance: This study was inspired by everyday observations, this leads to that the study findings can be applied on daily observations, at least the scenario of the inspiration. By using 304 stainless steel springs as experimental subjects, which is a material widely used in many fields, this study can provide valuable insights to different industries, this leads to a high ecological validity of the study and applicability of the study findings.

Controlled Variables: The study maintained strict control over many potential confounding variables such as spring dimensions, mass, humidity and surrounding temperature. By keeping these extraneous variables constant, the findings can be ensured that observed changes in the dependent variable were totally due to the independent variable. This promotes a higher internal validity of the study findings thus promotes a high reliability of the data collected.

Precision in Measurement: Fully applying digital tools like digital vernier callipers and digital infrared thermometers can minimise the potential human error which is inevitable when using traditional measurement tools and increase the accuracy of measurement. This precision of measurement of data can make the raw data collected more reliable and thus minimise the errors of following calculations, providing more accurate results. Using these tools not only brings convenience to the investigator but also allows a higher reliability of the data.

Limitations
Limited Temperature Range: In this study, it was conducted over a relatively narrow temperature range, this could lead to potentially missing the behaviours or phenomena that might occur at extreme temperatures. Also in this study, because of the lack of technology, there aren’t measurements and comparisons under specific temperature but using temperature ranges. This caused less valuable comparisons to be made under different temperatures which lowered the accuracy of the raw data.

Specific Material Focus: By only investigating 304 stainless steel springs, it cannot be known whether the study's findings can be applicable to springs made from other materials. Since different materials may react differently to temperature changes, this cause that there will be a low applicability of this study’s result on other materials’ spring, which lowered the ecological validity of the study

Short Duration: The study is a cross sectional study where it was conducted over a short period of time. This caused the long term effects of heating on the spring to be neglected. Under long term heating, springs might experience thermal expansion(Tevema.com), this might cause the dimensions of the spring to change and their properties might also change. In this study, this factor is lacking consideration so that the study might not be able to fully apply in real life, thus decreasing its ecological validity.

Improvements
Expand Temperature Range and use more accurate values of temperature: the study should be extended to include both lower and higher temperatures. This could cover more commonly used temperatures in factories, thus increasing its ecological validity. Moreover, accurate values should be used to measure in different trials. This can ensure a valid comparison between data collected in different trials to gain more information of the raw data.   
Include Diverse Materials: Testing springs made from different materials can further increase the study’s ecological validity. By investigating different springs and its behaviour under different temperatures, a better understanding of how temperature affects different kinds of metal springs can be gained. This can also increase the applicability of the study finding on various fields.

Long-Term Testing: conducting the experiment under a long time period and changing this study into a longitudinal study can help to further increase the ecological validity. By investigating the spring’s behaviour under a long time of extreme heating, it can provide a fuller picture of the behaviour of springs under different conditions, such as make the study findings more applicable under different situations.