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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 within about 2%. The launch angle can be chosen within a wide range. If the ball is thrown overarm, then the launch angle is just as important as the throw speed.

When a hard object rolls on a soft surface, or vice versa, rolling friction arises from deformation of the soft object or the soft surface. The friction force can be described in terms of an offset in the normal reaction force or in terms of energy loss arising from the deformation. The origin of the friction force itself is not entirely clear. It is investigated qualitatively in this paper by rolling a steel ball on soft foam and by rolling a foam cylinder on a hard surface. The deformation of the foam was observed visually, providing simple insights into the origin of the friction force.

A ball that rolls without sliding down an inclined plane requires a small static friction force to prevent the ball sliding down the incline. The magnitude of that force is investigated by considering the force needed to prevent the contact point from slipping.

Oblique angle collisions between two balls or two disks have been addressed by many authors. This paper describes oblique angle collisions between three or four billiard balls. Measurements and calculations are presented for cases where one ball is incident obliquely on two or three identical balls, which are in contact and initially at rest. Conservation laws alone are not sufficient to predict the outcome. Adding information about the impact forces on each ball (and ignoring friction forces) provides good theoretical agreement with experimental results. [ABSTRACT FROM AUTHOR]

Three simple experiments are described using a small water bottle with two holes in the side of the bottle. The main challenge is to predict and then explain the observations, but the arrangements can also be used for quantitative measurements concerning hydrostatic pressure, Bernoulli's equation, surface tension and bubble formation.

A well-known physics demonstration is to pull a tablecloth rapidly from under some crockery without disturbing the crockery. An interesting question is whether the same result can be expected if the crockery is replaced by a ball, given that the ball might roll backwards on the tablecloth. Theoretical and experimental results are presented showing that the result depends on the acceleration of the tablecloth. If crockery is at rest on a tablecloth, and if the tablecloth is pulled slowly, then the crockery will move at the same speed as the tablecloth. With a rapid pull, the crockery appears not to move at all. In fact, the crockery will move a small distance horizontally since the coefficient of sliding friction is not zero. The secret of success is to minimize the horizontal impulse, not by reducing the friction force but by reducing the time over which it acts.

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 that low bounce balls have a higher coefficient of rolling friction than high bounce balls.

The acceleration of a vehicle or a bicycle is commonly used in elementary physics courses to illustrate problems concerning Newton's laws of motion when friction forces are involved. The maximum possible acceleration is rarely discussed, although it is of interest to consumers and racing car enthusiasts, and it is sometimes questioned by students. It is the main focus of the present article and is considered from a basic physics point of view, appropriate for classroom discussion.

When measuring the speed of an object with a video camera, a correction may be needed for the time taken by the camera to acquire the image in each frame. Examples are given where the correction is quite significant.

An ice hockey player can strike a puck at speeds up to about 45 m/s (100 mph) using a technique known as the slap shot. There is nothing unusual about the speed, since golf balls, tennis balls, and baseballs can also be projected at that speed or even higher. The unusual part is that the player strikes the ice before striking the puck, causing the stick to slow down and to bend. There appears to be a significant advantage in hitting the ice before hitting the puck, otherwise hockey players would have learned from experience not to do that. In order to investigate the physics of the problem, the authors set up a simple experiment using a flexible meterstick to simulate a real hockey stick and mounted it as a pendulum so it could swing about an axis near the top end. The results presented in this paper support the fact that hockey players know what they are doing when they slap the ice, even though the result appears at first sight to violate conservation of energy.

In a recent article in this journal, Shakur described an interesting problem where a bullet of mass "m" strikes a block of wood of mass "M" and projects the block upward. The same problem was considered earlier by Cowley et al. and others. The main question of interest is whether the block rises to a greater height if it is struck in the middle rather than near one end. Conservation of energy or conservation of momentum arguments, on their own, appear to yield very different predictions. Both Shakur and Cowley et al. indicated that the block would rise to the same height, regardless of the impact point, based simply on a conservation of momentum argument.