If a smooth ball is dropped vertically without spin on a smooth horizontal surface then one might expect the ball to bounce vertically without spin. If it does not then the centre of mass of the ball does not coincide with its geometric centre. An experiment is described where a billiard ball and a superball are deliberately biassed by adding a…

If a ball rolls at constant speed on a horizontal surface about a horizontal axis then the angular velocity is easily measured. If the ball is projected with additional spin about the vertical axis, then the rotation axis is tilted and it is more difficult to measure the rotation speed. A few examples are presented to show how the separate topspin…

Newton's cradle is often discussed in science classrooms as a clear example of the laws of conservation of momentum and energy although it has been shown that this use is somewhat misleading. Approaches to understanding the behaviour of this apparatus are often over-simplified and deficient or over-complex and with little impact among teachers. In…

When a ball bounces obliquely on a horizontal surface, the bottom of the ball stretches horizontally and then vibrates backward. The resulting ball spin depends sensitively on the transverse vibration frequency. A simple model is presented to describe the effect, showing how the stored elastic energy can result in additional spin.

Newton's cradle is a well-known physics toy that is commonly used by teachers to demonstrate conservation laws in mechanics. It can also be used to investigate the physics of colliding objects, by recording motion of the balls on video film. Various experiments are described using 3-ball and 5-ball cradles, showing how different types of collision…

The vertical bounce of a plastic egg was investigated by dropping the egg on a horizontal surface and filming the result with a video camera. If the egg is dropped on one end then it bounces just like a spherical ball. If the top end of the egg is pointing forwards or backwards when it lands on the surface, or if the egg is spinning when it lands,…

If a small object is placed under the front leg of a chair, the chair tilts backwards. If the object is placed under a rear leg, the chair tilts sideways. The effect is surprising but can be analysed in terms of elementary physics.

A simple throwing task is described to illustrate various aspects of projectile motion. The task was to throw a tennis ball in a waste paper bin about 2 m away. Success depends on skill, but it also depends on the physics of the problem. If the ball is thrown underarm, then success depends primarily on the throw speed, which must be controlled to…

A spinning top or a spinning hard-boiled egg is fascinating to observe since both objects can remain upright for a relatively long time without falling over. If spun at sufficient speed on a horizontal surface, the spin axis rises to a vertical position and the bottom end tends to remain fixed in position on the surface. If the initial spin is…

It has been the author's experience over many years, no doubt shared by others, that a stick of chalk usually breaks into three pieces when accidentally dropped onto the floor. I rarely gave it any thought, apart from noting that the fundamental mode of vibration of a freely supported, rigid rod has two nodes at an equal distance from each…

A simple experiment is described to measure the coefficient of rolling friction for a low bounce ball rolling on a horizontal surface. As observed previously by others, the coefficient increased with rolling speed. The energy loss due to rolling friction can be explained in terms of the measured coefficient of restitution for the ball, meaning…

Almost everyone will have observed a spinning coin fall to a shuddering stop. How and why does it do that? Several experiments are described, suitable for a student project, to help motivate an understanding of the rotational dynamics involved.

In 1974, Professor Eric Laithwaite demonstrated an unusually heavy gyroscope at a Royal Institution lecture in London. The demonstration was televised and can be viewed on YouTube. A recent version of the same experiment, together with partial explanations, attracted two million YouTube views in the first few months. In both cases, the gyroscope…

The act of swinging an object such as a hammer or a tennis racket involves the application of forces and torques in a manner that is intuitively obvious to the person performing the task, but is probably much less obvious to the average physics student. This article describes the basic mechanics of the problem.

How would a physicist describe the elastic properties of an apple or a banana? Physics students and teachers are familiar with the elastic properties of metal springs, but are likely to be less familiar with the elastic properties of other common materials. The behavior of a metal spring is commonly examined in the laboratory by adding masses to…