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Golf Coefficient of Restitution (COR)

Golf Coefficient of Restitution (COR)

Golf Coefficient of Restitution (COR)

Or Newton’s Natural Law of Impact. Either way, it’s the measurement of energy loss or retention when two objects collide — like a golf club and ball, for instance.

Here you can see how a ball compresses when it strikes a club head, which means that the coefficient of restitution (COR), or efficiency of energy dispersed, can never be a perfect in golf. Even if that was scientifically possible. In fact, there are USGA COR limits.

Here you can see how a ball compresses when it strikes a club head, which means that the coefficient of restitution (COR), or efficiency of energy dispersed, can never be a perfect in golf. Even if that was scientifically possible. In fact, there are USGA COR limits.

Coefficient of Restitution (COR or C.O.R.) is a common physics measurement. Simply put, it is the amount of energy maintained or that dissipates when two objects collide. In golf, that almost always means judging how effectively the clubface strikes a ball. So, more COR means a ball will travel farther when hit with a club, usually a driver.

Sometimes, COR in golf is referred to as the spring-like effect a ball has coming off of a club (This has been a popular trend with thin-faced metal woods.). But there has been some debate about whether that actually takes place. 

The USGA actually has set a limit for manufactures about how much COR can be retained, or .83 (More on the equations below.). A perfect score where all energy is retained would be a 1.0, which is impossible in golf since a clubface and a golf ball are made of materials of unequal density. It’s widely believed that the closest to a perfect COR measurement found in sports is when two pool balls collide.

The least amount would be a 0.0. A common example of that used by physics teachers is if two pieces of gum collide midair and glob onto each other.  

Physics' Coefficient of Restitution (COR) equation and below it how COR applies to golf.

Physics’ Coefficient of Restitution (COR) equation and below it how COR applies to golf.

   

How COR typically is measured in the world of golf, or a measurement of how energy efficient a club is when it hits a ball.

How COR typically is measured in the world of golf, or a measurement of how energy efficient a club is when it hits a ball.

The belief is that a golf club with a higher COR than another, and if the club speed stays the same, will generate a longer carry for the same ball by at least several yards to the hundredth of a decimal point. 

Because of the USGA’s standardization, COR isn’t advertised as much as it once was. But golfers still take it into consideration and argue over whether it can be measured accurately considering all the different factors that really go into hitting a club and ball, such as torque, miss-hits, club length, etc…

For instance, golf balls have a COR of “about” 0.78, however, that can vary depending on what ball makers call a compression rating or the hardness of the golf ball. 

As an aside, in 2002, the USGA ruled that .83 was enough COR for golf — or an 83 percent transfer of energy from club to ball — after TaylorMade introduced a driver that could generate a .86 COR score. In addition, scientists say it is impossible to ever achieve a perfect COR score in golf because the ball and face are made of distinctive materials and have different masses and weights. 

Here's a look at how both the ball and clubface deflect or compress upon impact, which effects COR numbers.

Here’s a look at how both the ball and clubface deflect or compress upon impact, which effects COR numbers.

Check out this fascinating YouTube video from Titleist showing — and explaining — in detail exactly what occurs when the clubface strikes a golf ball:


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