Overview
This lecture explains how to investigate the relationship between force and extension in a spring using a required practical setup, including graphing results and understanding key concepts like linearity, elasticity, and spring constant.
Setting Up the Experiment
- Use a clamp stand, two bosses, two clamps, a heavy weight (to stabilize), a meter rule, and a spring.
- Ensure the top of the spring is at zero on the vertical meter rule for accuracy.
- Attach a horizontal wooden splint as a pointer to the bottom of the spring.
- Record the unstretched length of the spring as the baseline.
Conducting the Experiment
- Add a 1 newton weight to the spring; record the new pointer position.
- Continue adding 1 newton increments, recording the position each time.
- Calculate extension for each weight by subtracting the unstretched length from each reading.
Plotting and Interpreting the Graph
- Plot extension (y-axis) against weight (x-axis) to produce a graph.
- For a spring, the graph is a straight line through the origin, showing direct proportionality (linear relationship).
- Use the graph to determine the weight of an unknown object by measuring its extension and reading the corresponding weight.
Key Concepts
- Linear graphs (straight lines) show direct proportionality between force and extension.
- Nonlinear relationships (e.g., rubber bands) do not produce straight line graphs.
- Springs are elastic if extension returns to zero when force is removed.
- Overstretching the spring leads to a nonlinear graph, showing inelastic deformation and exceeding the limit of proportionality.
Calculating the Spring Constant
- Use the equation: Force = spring constant × extension (F = k × x).
- Determine the spring constant (k) by dividing force by extension (k = F/x) within the linear region of the graph.
- The spring constant remains consistent if the spring is not stretched beyond the limit of proportionality.
Key Terms & Definitions
- Extension — The increase in length of the spring due to an applied force.
- Elastic deformation — The spring returns to its original length after removing the force.
- Inelastic deformation — The spring does not return to its original length after overstretching.
- Limit of proportionality — Maximum point up to which force and extension remain proportional.
- Spring constant (k) — A measure of the stiffness of the spring; ratio of force to extension.
Action Items / Next Steps
- Practice the required practical setup and calculations.
- Review how to plot and interpret force-extension graphs for springs.
- Solve workbook questions on this practical for exam preparation.