Hooke’s law: the spring constant
Load a spring step by step, measure its extension and find the spring constant.
Objectives
- Measure extension for a series of loads.
- Show that extension is proportional to force.
- Find the spring constant and recognise the elastic limit.
Theory
Hooke’s law: within the elastic limit, the extension of a spring is directly proportional to the stretching force, F = kx. The constant k (N/m) measures stiffness. Beyond the elastic limit the spring does not return to its original length and the law no longer holds. The weight of a mass m is F = mg, so 100 g weighs 0.98 N.
F = kx F = mg
Procedure
- Read the pointer with no load on the spring.
- Add masses and read the pointer for at least five different loads.
- Plot pointer reading against force in the Graph tab and note the gradient.
Precautions
- Read the pointer at eye level.
- Do not load the spring beyond 500 g.
- Wait for the spring to stop bouncing before reading.
- Subject
- Physics
- Grade
- 9–11
- Chapter
- Force and Motion (Nepal National Curriculum (CDC), grade 9)
- Difficulty
- Easy
- Duration
- 20 min
- Safety level
- Low
- Version
- 1.0
Apparatus
- Helical spring
- Stand
- Pointer
- Metre rule
- Slotted masses
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