Friction Concept

Demonstrations in Friction

A smaller polished metal block resting on a larger darker metal block, both showing scratched and worn surfaces

Friction Surfaces

Rubbing two metal blocks together produces a grating sound, making audible the microscopic surface interactions that cause friction. Students hear direct evidence that friction converts mechanical energy into sound and …
Two wooden blocks arranged in series on a demo bench, connected by string to a large circular 20 N spring scale with red needle, pulled by hand

Sliding Blocks

Demonstrates that friction force is independent of contact area. Blocks pulled in series (large contact area) and stacked (small contact area) require the same force on the spring scale, directly …
Five sets of interleaved pastel-colored index card stacks with black binder clips, hanging vertically and showing progressively more overlap from right to left

Lifting Weights with Paper

Interleaved index cards and a folded paper loop demonstrate that friction scales with the number of contact surfaces and with perpendicular applied forces. Doubling the number of overlapping card sections …
Wooden inclined plane tilted at an angle with a block and binder-clipped masses on top, a large brass protractor at the base, assorted wooden blocks with different surfaces, and black hooked masses on a wooden platform

Block on Inclined Plane

Shows that the critical angle for sliding on an incline depends only on the coefficient of friction, not on mass. Adding weight to a block does not change the angle …
Wheel with tan plastic spokes and knobby black rubber tire on a metal axle, with chalk nearby and tread-pattern marks visible on the chalkboard behind

Rolling vs. Skidding

A chalked wheel rolled along a blackboard leaves a clear tread pattern; the same wheel dragged (skidding) leaves a smeared streak. This contrast shows that rolling involves static friction (no …
Two large tan cylindrical rollers mounted on black metal bearings on a wooden base, with a meter stick resting across them. A hand positions the stick. A pulley and belt are visible on the right side.

Oscillating Meter Stick

Demonstrates that friction is proportional to normal force. As a meter stick's center of gravity shifts between two rotating rollers, the normal force distribution changes, causing the dominant friction force …
Hand holding a red matchbook horizontally with string running to a horizontal rod on a stand; keys hang vertically on the other side with slight motion blur

Key and Matchbook Windlass

A matchbook and keys hang on opposite ends of a string draped over a horizontal rod. When released, the keys fall while the matchbook swings like a pendulum, wrapping the …