# With the help of physics, a teenage pool player goes pro

Big shot: with the help of physics, a teenage pool player goes pro

Andrew Klein

Austin Murphy, 13, sizes up the balls that are scattered around the pool table. A crowd of adults has gathered around, but Austin puts them out of his mind. Concentrating only on the game, he sinks the shot.

Regulars to the local pool hall in Folsom, California, know that Austin is a force to be reckoned with. He started playing pool when he was just 5 years old. Now he is the youngest professional competitor on the International Pool Tour. His secret? “You need to know about geometry and physics,” says Austin.

BILLIARD BASICS

Knowing principles of physics alone won’t make you a great pool player, says David “Dr. Dave” Alciatore, a professor of engineering at Colorado State University. But it can certainly give you the upper hand against even your fiercest opponents.

Common sense–and basic physics laws–tells Austin that when he hits the cue ball with his pool stick, the ball will roll forward. If his aim is on target, the ball will hit a colored ball. The law of conservation of energy ensures that when the two balls collide, the cue ball will transfer some of its kinetic energy (energy of motion) to the colored one. The energy from the cue ball isn’t lost; it’s just shared between the two balls–shooting the colored ball across the table.

ON THE MOVE

When the balls knock against each other, the cue ball also transfers momentum to the colored ball. Since an object’s momentum is equal to its mass multiplied by its velocity, the quicker a billiard ball is moving, the greater its momentum.

If Austin smacks the colored ball straight on with the cue ball, the cue ball will transfer all of its momentum to the other ball. This will cause the cue ball to stop completely. But this pool whiz also knows that if he were to hit the cue ball so that it collides on an angle with the colored ball, both balls would deflect in a V-shape, or 90[degrees] angle (see Nuts & Bolts, right).

TRICK SHOT

Austin has other tricks up his sleeve: For instance, he uses a technique called “Draw” to put backspin on the cue ball. How? He hits the bottom of the cue ball to make it spin backward, even as it moves forward. After the cue ball hits a colored ball, the backspin will cause the cue ball to slowly roll back toward Austin. Similarly, in a move called “Follow,” Austin hits the top of the cue ball to give it topspin. This causes it to continue to roll forward after striking a colored ball. “[This] helps to set up the cue ball for the next shot,” explains Austin.

What’s the best advice Austin has for up-and-coming pool players? “Visualize the shot in your head and take a few deep breaths,” says Austin. “If you aren’t confident, you won’t make the shot.”

nuts & bolts

1 90-DEGREE RULE: When the cue ball hits another ball at an angle, both balls deflect at a 90[degrees] angle.

2 DRAW: When the pool stick hits the bottom of the cue ball, the ball moves forward and gains backspin. The result: After the cue ball hits the colored ball, the cue ball will roll backward.

3 FOLLOW: When the pool stick hits the top of the cue ball, the bali moves forward and gains topspin. The result: After the cue ball hits the colored ball, the cue ball will roll forward.

web extra

See Professor Alciatore’s video explanations of various pool shots at: www.engr.colostate.edu/~dga/pool/normal_videos/index.html

* When the first pool tables were developed in the 1600s, they had fiat vertical walls on each side to keep the balls from rolling off the tables. Soon players found that aiming a ball at a wall, instead of directly at a pocket, could be beneficial for some plays. When the ball collides with the wall, the wall may push and redirect the ball toward a desired direction. How does a cue ball colliding with a colored ball change the way both balls move?

* The game of pool was adapted from an outdoor version of the game, which was popular in 15th-century Northern Europe. When the game moved indoors and onto tables instead of lawns, the tables were covered with green cloth to symbolize the grass. The balls were pushed with bulky wooden sticks called “maces.” Thin pool sticks were not invented until the late 1600s. How does the aim of a pool stick affect how a cue ball moves?

CRITICAL THINKING:

* Austin Murphy started playing pool because it was a game that he could play with his brother who is in a wheelchair. Can you think of some other sports or games that Austin could share with his brother? Discuss with your class the different aspects of the games and why they would be ideal for someone in a wheelchair.

CROSS-CURRICULAR CONNECTIONS:

MATH: Momentum is equal to an object’s mass multiplied by its velocity. If a cue ball weighs 0.17 kilograms (0.35 pounds) and is moving at a velocity of 48 kilometers per hour (30 miles per hour), what is the momentum of the ball?

Answer: 8.16 kg x km/hr (10.5 lbs x mi/hr)

RESOURCES

* This Web site from the Billiards Congress of America has a brief history of billiards, including how the game and equipment were developed: www.bca-pool.com/aboutus/history/start.shtml

* Learn some basic rules and vocabulary of billiards games. Check out: www.uoregon.edu/~pegr/html/billiards.html

* For a great set of math lessons and activities related to billiards, be sure to check out this Web site: http://illuminations.nctm.org/LessonDetail.aspx?ID=U125

DIRECTIONS: Fill in the blanks to complete the following sentences.

1. When a cue ball collides with a colored ball, it transfers some of its — –, or energy of motion, to the colored one.

2. An object’s momentum is equal to its — multiplied by its –.

3. When a cue ball transfers all of its momentum to another ball, it will cause the cue ball to — –.

4. If a cue ball collides on an angle with a colored ball, both balls would deflect in a V-shape at a — angle.

5. When the pool stick hits the bottom of the cue ball, the ball moves forward and gains this type of spin: –. After the cue ball hits the colored ball, the cue ball will roll –.