Lifting Weights with Paper - Physics Demonstrations - Lifting Weights with Paper | Physics Undergraduate Labs

Purpose

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 approximately doubles the maximum supported mass, countering the misconception that friction depends on contact area.

Five sets of interleaved pastel-colored index card stacks with black binder clips, hanging vertically and showing progressively more overlap from right to left

Ring stand with rod and ring clamp holding interleaved cards, brass masses on the bench below, and packing foam at the base

Two interleaved phone books — a white pages directory and a CU Boulder 2002 yellow pages — with pages shuffled together

A tall stack of heavy iron disk masses on a mass hanger, with a small folded paper loop and a small brass mass shown beside it

Figure 1: Five card sets with 1, 2, 4, 8, and 16 overlapping sections (right to left). Each stack contains 32 cards (~50 g with clips).

Figure 2: Ring stand setup with interleaved cards hanging from ring clamp. Brass masses are added to the lower clip until the cards separate.

Figure 3: Two interleaved phone books. Hundreds of interleaved pages create thousands of friction interfaces, making them virtually impossible to pull apart.

Figure 4: The folded paper loop (lower left) can support over 10 kg of disk masses when the joint is at the bottom, because the load creates compressive normal force at the overlap.