Cross, Rod
Published in
Physics Education

A tennis ball with string around an equator was allowed to fall like a yo–yo. Measurements and calculations are presented on the total work done on the ball to increase its translational and rotational kinetic energy.

Kok, Karel Priemer, Burkhard
Published in
Physics Education

In this lab activity, carbon copy paper is used to record the horizontal distance a marble flies off a table after rolling down an incline. The minimal scatter of the dots visually shows the high precision—i.e. the small uncertainty—of the measurements to students. The theoretical prediction of this distance will be too big if students forget to in...

Cross, Rod
Published in
Physics Education

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.

Cross, Rod
Published in
Physics Education

Newton’s cradle is commonly used to show that a collision of three or more identical balls in a row is one that conserves momentum and kinetic energy. An experiment is described where one billiard ball collides at an angle with another two at rest. The collision also conserves momentum and kinetic energy and has several surprisingly simple outcomes...

Cross, Rod
Published in
Physics Education

Experimental results are presented concerning the motion of a ball that bounces up an incline a few times then bounces back down again. The number of bounces up the incline is typically small since the speed of the ball in a direction parallel to the incline decreases rapidly, not only during each bounce but also while the ball is in the air. The b...

Cross, Rod
Published in
Physics Education

A collision of one object with two or more objects is relatively complicated in general, but a simple example is provided by Newton’s cradle since all the objects are identical and in line. In the present paper, an experiment is described where a heavy mallet collides head-on with two billiard balls. The two conservation equations indicate that man...

Cross, Rod
Published in
Physics Education

When two billiard balls collide head-on on a smooth, horizontal surface, momentum and kinetic energy are both conserved to a good approximation. If the experiment is repeated with two rubber balls, then kinetic energy is not conserved and neither is momentum. The latter result can be explained in terms of the external friction forces involved.

Gratus, Jonathan
Published in
Journal of Physics A: Mathematical and Theoretical

Since a classical charged point particle radiates energy and momentum it is argued that there must be a radiation reaction force. Here we present an action for the Maxwell–Lorentz without self-interactions model, where each particle only responds to the fields of the other charged particles. The corresponding stress–energy tensor automatically cons...

Zhao, Shuang-Ren

When studying the energy principle of N current elements, the author found that the Poynting’s theorem of N current elements is very similar to the principle of mutual energy, except that the subscript of the summation symbol is different. Because the mutual energy principle of N current elements and Poynting’s law of N current elements are all ene...

Staley, Richard
Published in
History of science

This paper highlights the significance of sensory studies and psychophysical investigations of the relations between psychic and physical phenomena for our understanding of the development of the physics discipline, by examining aspects of research on sense perception, physiology, esthetics, and psychology in the work of Gustav Theodor Fechner, Her...