OPOpenPithMake curiosity visiblePhysics lab / Motion and force

About this lab

Five experiments, one thread: how force changes motion.

The first two only describe motion: the ticker tape shows speed changing evenly, and the Newton tube shows that without air everything falls equally fast. The last three ask why: where friction comes from, how net force and acceleration are related, and why a scale reads differently in an elevator.

Every reading, dot and curve comes from the same physical model, not a pre-drawn animation. Change one parameter and all the data is recalculated together.

Model and sources

Model and sources

  • Ticker tape: friction is balanced, a = mg / (M + m); after the mass lands the cart moves steadily. Positions are read to 0.1 mm.
  • Newton tube: air drag is proportional to speed squared, and terminal speed is inversely proportional to the square root of the pressure; in a vacuum t = √(2L/g).
  • Tilting board: at rest, static friction f = mg sinθ, up to μs·N; sliding, f = μk·N.
  • Photogates: v = d / Δt, a = (v₂² − v₁²) / 2L; taking the pull as the hanging weight overstates it by m / (M + m).
  • Elevator: scale reading = normal force N = m(g + a), shown in kg.

g is the textbook value 9.8 m/s². The friction coefficients for towel, wood and glass and the terminal speeds of the coin and feather are teaching assumptions for comparison, not measurements. Arrow lengths are only proportional sketches.

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