Let's talk cushion bounces

The way snooker balls interact with cushions is a complex interplay of physics, material properties, and maintenance.

Why do cushions on different snooker tables react differently?

Cushions react differently due to a combination of factors:

 * Rubber Quality and Age: The core of a snooker cushion is typically vulcanized rubber. The quality of this rubber, its density, and its elasticity vary between manufacturers and grades. Over time, rubber hardens and loses its elasticity, leading to "dead" cushions that absorb more energy and provide less rebound.

 * Cushion Profile and Construction: Snooker cushions have a specific "L77" profile. Variations in this profile, or the way the rubber is attached to the rail (e.g., steel block cushions vs. wooden rails), can significantly affect how the ball interacts with the cushion. Steel block cushions are generally more rigid and provide a more consistent rebound.

 * Cushion Height: As discussed below, the height of the cushion's "nose" (the point where the ball makes initial contact) relative to the ball's center is crucial. Slight variations can alter the ball's spin and rebound angle.

 * Cloth Tension and Condition: The cloth covering the cushions also plays a role. If the cloth is loose, worn, or dirty, it can affect the friction and energy transfer during impact.

 * Table Levelness: An unlevel table can subtly change the effective angle of incidence for the ball, leading to unpredictable cushion reactions.

Why do balls jump when they make contact with the cushion?

Balls jumping off the cushion, especially at high speeds, is generally undesirable and can be caused by:

 * Incorrect Cushion Height: If the cushion's nose is too low relative to the ball's center, the ball can "dig in" and be propelled upwards. The ideal height is empirically determined to minimize this hop.

 * Topspin: If a ball hits the cushion with significant topspin, especially at a low cushion height, the topspin can convert into an upward motion.

 * Deformation of Ball and Cushion: At high speeds, both the ball and the rubber cushion deform upon impact. If the cushion deforms in a way that creates an upward force, the ball can jump.

 * "Pinch Effect": In rare cases, if cushions are set up slightly off, they can create a "pinch" effect that causes the ball to jump.

* Dirty balls: Dirty balls will increase jumping off the cushion created by more friction on impact.

Why does the object ball or cue ball slow down after hitting a cushion on a new cloth?

Balls will always slow down after hitting a cushion because no collision is perfectly elastic. Energy is lost due to:

 * Inelastic Collision: Some kinetic energy is always converted into other forms, like heat and sound, during the impact. The rubber cushion absorbs and then releases energy, but not all of it is returned to the ball's kinetic energy. This energy loss is quantified by the coefficient of restitution, which is less than 1.

 * Friction with Cloth: Even on new cloth, there's friction between the ball and the cushion cloth. This friction dissipates energy. Because the balls slide at first there is a loss of energy due to the reversing back to a rolling motion.

 * Deformation: The temporary deformation of both the ball and the cushion rubber consumes energy.

New cloth specifically might make the ball feel like it slows down more because the cloth offers more resistance than worn cloth, especially due to its nap. While the actual energy loss from the cushion impact itself might not be drastically different, the overall effect of the new cloth (more slide on the bed and cushion) contributes to the perception of slower ball speed.

Why do clean balls slow down after making contact with the cushion?

The same reasons apply as above:

 * Inelastic Collision: Even with perfectly clean balls, the collision with the cushion is not perfectly elastic.

 * Friction: Friction between the clean ball surface and the cushion cloth still exists and dissipates energy.

Dirty balls might experience less friction and thus slow down less then clean balls wich still experience the fundamental physical principles of energy loss by more absorption of energy due to excessive slide during a collision.

Why does the angle go longer on new cloth and clean balls?

 * Less Friction on Cloth: New cloth, being less worn and often having a more consistent nap (or less nap, depending on the type), generally provides less rolling resistance for the ball. This means the ball maintains more of its speed and spin as it travels across the table before and after hitting the cushion.

 * Consistent Cushion Rebound: New cushions, often found on tables with new cloth, tend to have more consistent and predictable rebounds. This, combined with less friction on the table, allows for more accurate and "longer" angles (meaning the ball travels further along its intended path after the rebound).

 * Less Spin Degradation: Clean balls and new cloth mean less friction degrading the ball's spin as it travels. Spin significantly influences the rebound angle. If spin is maintained better, the intended angle will be held longer.

Is cushion height important?

Yes, cushion height is extremely important! It's a critical factor in how the ball reacts off the cushion.

 * Optimal Contact Point: The "nose" of the cushion needs to make contact with the ball at a specific height relative to the ball's center to ensure a consistent and predictable rebound. This height is typically around 63.5% of the ball's diameter.

 * Spin Interaction: This specific height is chosen to optimize the interaction between the ball's spin and the cushion. If the height is too low, the ball can hop or jump. If it's too high, it can drive the ball into the table, leading to excessive slowdown and cloth wear.

 * Rebound Angle and Speed: Incorrect cushion height can lead to inconsistent rebound angles and speeds, making precise play very difficult. Professionals are highly sensitive to even tiny variations.

Does the cushion need to be covered with thicker cloth?

Generally, snooker cushions are covered with a specific type of wool cloth (often called "baize") that is dense and durable. While the thickness is important for durability and consistent play, a thicker cloth on the cushions will guarantee more reliable cushion bounces.

 * Durability and Performance: The cloth needs to be robust enough to withstand repeated impacts without tearing or fraying, while also providing the right amount of friction for ball control.

 * Energy Transfer: The cloth's weave and tension affect how much energy is transferred or absorbed during impact. A consistent, well-tensioned cloth is crucial.

 * Friction: The thickness and nap of the cloth influence the friction between the ball and the cushion. Too thick or too nappy, and it could excessively slow the ball or alter its spin in unpredictable ways.

In summary, the performance of snooker cushions is a finely tuned system. Any variation in the materials, construction, or maintenance can have a noticeable impact on how the balls react significantly influencing the game.