This paper presents a theoretical analysis and experimental exploration of the 9th problem, “Oscillating Screw,” in the 2023 International Young Physicists' Tournament (IYPT) from a dynamic perspective. The problem describes the release of a screw on a slope, which may generate increasing oscillations as it moves down the slope. In this paper, the reason for the increase in oscillation amplitude is explained through force analysis during the sliding process and verifies it through experiments. In addition, simulation software is used to explore the effects of different parameters on the motion through simulation.

A table tennis ball is floating in a cup of water. After the cup is dropped and collides with the ground, the table tennis ball will get launched to a great height. During the free falling of the cup, the gravity and the buoyance applied on the ball vanish in the reference frame of the cup, and the ball is sucked into the water due to the interfacial tension. When the cup collides with the ground, the intense deceleration process leads to an enormous buoyance acting on the ball. Under the influence of this buoyant force, the table tennis ball is ejected from the cup, and the ejection velocity of the ball is directly proportional to the impact velocity of the cup.

This paper provides a simple physical picture for the azimuthal-radial pendulum which was presented by the 31st International Young Physicists' Tournament (IYPT2018). Through equivalent analysis, the azimuthal radial pendulum can be regarded as a double-filament pendulum with different lengths in two mutually perpendicular directions. Due to the different vibration frequencies in the two perpendicular directions, the trajectory of the pendulum bob exhibits a Lissajous figure. This paper also demonstrates through experiments the consistency of the trajectories between the azimuthal radial pendulum and the double-filament pendulum.

For a bead placed on a rotating ring, when the ring rotates, the beads will produce a series of motion behaviors. The bead can be considered as a rigid body. Two forms of resistance, rolling friction and viscous resistance, are considered, and their equations of motion are derived by analytical mechanics. Relevant kinetic variables are discussed, including supercritical pitchfork bifurcation at the equilibrium point, small vibration period, which are verified one by one through the experimental model. The forced vibration under special conditions is studied theoretically and experimentally.