(S&D) Safety & Defense - Energy Transfer Calculations

(About the author)

Safety Toolbox (Advanced)

(This is today's bit of advice from the book Safety Toolbox.)

When contacting the cue ball with your cue tip, the energy put on the cue ball depends on the forward speed of the cue stick. Following that contact with its initial momentum, the balls start losing energy from various factors. Eventually, all of the energy from the stroke is dissipated and the balls stop moving.

Cloth resistance

As balls travel across the table, they lose energy through friction. Balls stop rolling quickly on the thicker cloth and travel further on thinner material. Bar tables usually have thicker cloth to withstand the wear and tear from careless players.

Tournament cloth on professional pocket billiard tables is of very good quality, with a short nap (hairs that stick up). Balls roll greater distances because friction is less. This type of cloth is the gold standard for well-run pool halls and high quality home pool tables.

In billiards, a very thin cloth is used. This ensures that the balls (larger and heavier than pool balls) travel much further. To enhance the rolling distance, the slate is heated. If you have access to a billiards table, this is an excellent opportunity to work on controlling very soft strokes.

Cushion absorption

Cushions on table rails (also known as rubber) come in a variety of qualities. Cheap rubber absorbs impact energy and the ball comes out at slower speeds. The loss can be as much as 40-50% of the energy.

Expensive rubber absorbs much less of the ball's energy. The best pool rubber only absorbs about 20-30% of the ball's energy. A good comparison between the high and low qualities would be the difference between the bounce of a tennis ball and a super ball.

Two other factors affect the cushion reaction. One of these is how well the rubber is attached to the wooden rail. If there is any gap between the rubber and wood, the energy is absorbed so much that the ball almost dies close to the rail. This is known as a "dead" rail.

The other factor is when the rail is mounted incorrectly. If the nose of the rubber is too high, it partially traps the incoming ball underneath and kills the ball speed and angle. Too low causes the ball to jump into the air (and can help the ball bounce off the table).

Between balls

When a moving ball contacts another ball, a certain amount of energy is transferred from one to the other. The thinner the angle of contact, the more energy stays with the first ball. The fuller the contact, the less energy stays with the first and the more action the second has. With the full hit, the majority of the energy is transferred and the second ball can travel greater distances. (This ignores the action of the first ball when it has draw, follow, and/or side spin.)

When the object ball is contacted at various angles, the amount of energy transfer can be roughly calculated to determine how far the first ball and second ball travels across the table. (Some energy is lost when a moving ball hits a stationary ball.) As a general rule, use these approximate transfer calculations:

  • Thin hit (10% or less transfer)
  • 1/4 ball hit (25% transfer)
  • 1/2 ball hit (50% transfer)
  • 3/4 full hit (75% transfer)
  • Full head-on hit (100% transfer)

Summary

This knowledge is necessary when playing safeties where you intend to achieve precise ball placement. Master ball control and you can take it to any table. A few ball rolls and you automatically adapt to the playing conditions.

All of this information might seem a bit confusing, but it's a lot easier to put it all together than you might think. You don't have to know the exact percentages of energy loss or transfer. You do have to know how far balls can travel with a given speed on different tables. Perform various ball control exercises that you have mastered. Your brain will make some automatic adjustments to your speed control. This builds up some experience in expecting consistent results.

 

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