This paper has a pedagogical aim. Indeed, by using the relativistic velocity-addition and Einstein's equivalence principle (EEP), we want to analyse in a simple way the physics of time on a rotating non-inertial frame. We use a didactic approach considering four friends. The first is in the laboratory, the second at rest on the disk at radius r,…

An experiment is described where a billiard ball and a golf ball were projected with backspin on a horizontal surface to measure the transition from sliding to rolling. During both phases, the torque on the ball is affected by an offset in the line of action of the normal reaction force.

A simple experiment is described to compare the descent time between two vertically separated points when an object slides down tracks of varying shape. A surprising result is that the descent time is shortest when it follows a circular track rather than a cycloidal track. Cycloidal tracks are usually predicted to result in the shortest descent…

The question of how the processes around the Faraday generator with its rotating magnet should be interpreted has been controversial since its discovery by Faraday. Does the magnetic field rotate together with the rotating magnet or does it remain stationary? Furthermore, does one only need Faraday's flux law to interpret inductive processes, or…

A loop-the-loop experiment is described to show how sliding friction affects motion of the ball. Conservation of energy can be used to explain the basic physics, but significant energy loss is observed in practice and expands the usefulness of this apparatus as a teaching tool.

An experiment is described where a pendulum bob was allowed to roll back and forth across an inclined plane. The period of oscillation is larger than that for oscillation in a vertical plane, in part because the effective value of "g" is reduced on an inclined plane. The experiment highlights the differences between all three common…

Calculating the duration of a motion when the applied net force on the moving body changes with time is usually a challenging task. In most cases, the only example of the duration of a motion when the acceleration is not constant presented to introductory physics students worldwide is the example of harmonic motion. A discussion with respect to…

A standard physics experiment for students is to measure the terminal velocity of an object in air or in glycerine. A more difficult challenge is to measure the terminal velocity in water since the depth of the water needs to be large or the object needs to be dropped in the water at a speed close to its terminal velocity. Results obtained by…

Implementing smartphones with their internal sensors into physics experiments represents a modern, attractive, and authentic approach to improve students' conceptual understanding of physics. In such experiments, smartphones often serve as objects with physical properties and as digital measurement devices to record, display, and analyze…

In a 1993 book review, E. Pearlstein asks, "Why don't textbook authors begin their discussion of magnetism by talking about magnets? That's what students have experience with." A similar question can be asked, "Why don't professors have students measure the force between permanent magnets in introductory physics labs?" The…

A solid ball placed on a rotating turntable is known to roll slowly around a circular path, at a speed 3.5 times slower than the turnable itself. If the ball is located in a straight track across a diameter of the turntable, then it accelerates rapidly to the edge. Both effects were filmed in slow motion using a video camera and a cake decoration…

As a boy I spent many hours skipping stones across the surface of the water on the shore of Lake Michigan. The challenge was to get as many skips or as much distance as possible. Zero skips was a bust. One or two skips was disappointing, three or four skips was mediocre, and six or more skips was exhilarating. The angle of the stone with respect…

The motion of a bead along a path restricted to straight lines (restricted brachistochrone), sliding without friction from rest and accelerated by gravity, is considered. For two shapes of path, the geometry of the route optimized to provide the least travel time from one point to another is obtained. The bead's travel times, path lengths, and…

A bouncing rubber ball under a motion sensor is a classic of introductory physics labs. It is often used to measure the acceleration due to gravity, and can also demonstrate conservation of energy. By observing that the ball rises to a lower height upon each bounce, posing the question "What is the main source of energy loss?" and…

In recent years, smartphone sensors have been frequently used in educational demonstrations to improve students' understanding of certain physical kinematic topics. In particular, the sensors on modern smartphones enable students to use their phones as physics mini-laboratories, and they have been used to analyze objects' speeds and accelerations…