Precision spring dynamometer
Applies and measures the horizontal pulling force required to maintain steady slider motion with 0.02 N resolution.
Physics / Friction & normal force
FREE TO EXPLOREEXPERIMENT 15 · PHYSICS LABORATORY
The laws of friction: Determination of the coefficient of sliding friction
Investigate Amontons–Coulomb laws of friction and determine the coefficient of kinetic friction μ by linear regression of friction force against normal load. Explore a virtual apparatus, collect readings and analyse a graph.
CHANGE · OBSERVE · MEASURE
Your virtual workbench.
FRICTIONAL FORCE FF—
MEASUREMENT STATUS
Ready for a virtual observation.
Adjust the apparatus, then take a reading.
Readings are generated by an ideal model. The diagram is schematic and is not to scale.
Simulation assumptions and limits
The simulation assumes dry Coulomb friction between homogeneous rigid surfaces without thermal softening, surface wear degradation, or stick-slip resonance. Observations reflect polished wood-on-wood contact (reference μ = 0.350) with standard dynamometer reading resolution of 0.02 N.
Know your apparatus.
Weighted contact slider block
Provides uniform planar contact surfaces with captive tray for holding calibrated slotted weights.
Horizontal friction bed track
Provides a rigid, level, polished guiding surface for slider travel.
Set of calibrated slotted weights
Allows normal compressive force N to be varied systematically from 1.0 N to 14.0 N.
FOLLOW THE METHOD
A reason behind every step.
Investigate Amontons–Coulomb laws of friction and determine the coefficient of kinetic friction μ by linear regression of friction force against normal load. Suggested independent settings: 2.0, 4.0, 6.0, 8.0, 10.0 N.
Determine dynamometer horizontal zero correction
Hold the spring balance horizontally on the bench, tap gently to relieve internal spring friction, and record any zero-point offset.
Why this step matters
In a horizontal position, the spring does not support the hook self-weight, shifting the zero calibration compared to vertical suspension.
Level the friction track and clean contact surfaces
Verify with a spirit level that the track is strictly horizontal, and wipe both the slider base and track bed with clean lint-free cloth.
Why this step matters
Any slope introduces a gravitational component along the track, while dust or grease drastically alters the interfacial shear strength.
Place test weights on the slider
Load the slider tray with slotted weights to establish the desired total normal force N (slider tare weight plus added load).
Why this step matters
Distributing weights symmetrically over the slider ensures uniform contact pressure across the entire interface without tilting.
Apply steady horizontal traction
Connect the spring balance hook to the slider eyelet parallel to the bench and pull steadily until the slider transitions from static grip to uniform constant sliding.
Why this step matters
Pulling at an upward or downward angle alters the effective normal force by F sin(θ), corrupting the N-axis value.
Record kinetic friction reading during uniform motion
Note the force reading on the dynamometer while the slider is in steady, non-accelerating motion across the central test span.
Why this step matters
Static friction exhibits a peak threshold before motion; only steady motion measures the true kinetic coefficient μ_k.
Repeat systematically across the load range
Repeat the observation across all five independent normal loads from 2.0 N to 10.0 N to assemble the linear regression dataset.
Why this step matters
Testing across a wide range of normal loads verifies Amontons’ proportionality and minimizes slope estimation error.
YOUR NOTEBOOK · 0 OBSERVATIONS
Turn measurements into a result.
Points are your observations. The fit uses SI x and y values before display scaling.
LINEAR FIT · y = mx + b
F_f = μN + b
| # | Normal load N (N) | Frictional force Ff (N) | Normal load N (N) | Frictional force Ff (N) | Remove |
|---|
No readings yet. Take a virtual measurement and record it.
Calculate it yourself.
CHECK YOUR UNDERSTANDING