# Science of Golf: Kinematics

Air Date: 05/22/2013
Source:
NBC Learn
Creator:
Dan Hicks
Air/Publish Date:
05/22/2013
Event Date:
05/22/2013
Resource Type:
Science Explainer
NBCUniversal Media, LLC.
2013
Clip Length:
00:05:47

In order to measure the speed of a putting green, golf course superintendents use a device called the Stimpmeter. Adopted by the USGA in 1978, the Stimpmeter calculates green speed by relying on the principals of kinematics: position, velocity and acceleration. "Science of Golf" is produced in partnership with the United States Golf Association and Chevron.

Science of Golf - Kinematics

DAN HICKS, reporting:

In professional golf, everyone applauds the big hitters. But a player's short game is just as important, especially putting, which requires concentration, control and a skill known as "reading the green."

SUZANN PETTERSEN (LPGA Tour Player): When I’m looking at a putt and I’m reading the green, I’m trying to see the contours of the green so it's going to help me understand how the putt is going to break. Either it's a straight putt, maybe it's a left to righter, maybe it's a right to lefter, maybe it's uphill, downhill.

HICKS: Because putting greens vary in shape and size, greenkeepers work hard to control the speed of the green, a measurement of how much the ball slows down as it rolls across the putting surface.

DREW WEAVER (2009 U.S. Walker Cup Team Member): The speed of the green definitely affects the read of the putt and it's something you have to take into consideration.

HICKS: In order to measure the green speed, golf course superintendents use a device called the Stimpmeter. Steve Quintavalla is an engineer in the Equipment Standards department at the United States Golf Association.

STEVE QUINTAVALLA (Equipment Standards, USGA): The Stimpmeter is a ramp for rolling golf balls onto a turf at a fixed speed so that we can tell how much friction or rolling resistance a golf green has.

HICKS: In order to measure green speeds, the Stimpmeter relies on the principles of kinematics, a branch of classical mechanics that describes motion in three ways: position, velocity and acceleration.

QUINTAVALLA: The Stimpmeter counts on the acceleration of a golf ball due to gravity, the fixed speed that the golf ball will always have at the end of the Stimpmeter and then the distance that it travels under constant deceleration and changing velocity during its run on the grass.

HICKS: The first step to using the Stimpmeter is establishing the ball's position. Adopted by the USGA in 1978, the Stimpmeter is 36 inches long, has a notch located 29.4 inches from the end and is designed to release a ball from the notch when raised to the height of 21 degrees. In this case, the ball's starting position would be a defined location 21 degrees above the putting surface.

QUINTAVALLA: At 21 degrees we can tell how high the ball is off the ground and therefore how much gravity is going to accelerate the ball down the ramp so that when the ball hits the ground, it's always going the same speed.

HICKS: Speed is the distance covered by an object over a defined period of time. To find the ball's maximum speed at the end of the Stimpmeter, we must know the ball's average acceleration or change in speed over time. Since the ball always accelerates down the Stimpmeter at 8.4 feet per second per second, or feet per second squared, and takes .8 seconds to get to the bottom, its maximum speed is 6.4 feet per second. To define the ball's maximum velocity, simply add the direction it's moving, in this case 6.4 feet per second, south.

QUINTAVALLA: Right here the ball is at rest. It's not moving. When it lets go, it starts accelerating until it reaches the bottom of the ramp and that's when it going to go its maximum speed.

HICKS: Once the ball makes contact with the green, rolling resistance or friction created by the height of the grass, causes the ball to slow down resulting in deceleration.

QUINTAVALLA: It constantly has negative acceleration or deceleration until the resistance finally causes the ball to stop.

HICKS: To find the ball's average negative acceleration coming off the Stimpmeter, we subtract the ball's initial velocity from its final velocity and divide it by the time it takes to travel across the green, in this case 4 seconds. On a fast green, the ball has a smaller deceleration and rolls a longer distance. On a slower green, the ball has a bigger deceleration and rolls a shorter distance.

QUINTAVALLA: When we go to different golf courses and different greens on the same golf course, how far the ball rolls is only a matter of how much resistance or friction the green has.

HICKS: To calculate the speed of a green, three golf balls are rolled in one direction from the Stimpmeter along a 14 foot level area. The average distance of the three balls is calculated and then the three balls are rolled again in the opposite direction across the same line where the average distance is taken again. The average distances of both rolls determine the overall speed of the green.

WEAVER: Let's say your average green is probably an eight or nine, and faster greens on, you know, PGA Tour, U.S. Open, the Masters are twelve, thirteen, sometimes even fourteen on the Stimpmeter.

HICKS: Because putting greens can be big or small, undulating or flat, speed isn't the only challenge players face when reading the green.

PETTERSEN: It really comes down to a lot of feel because you can read a lot of different brakes, but then it also depends on what kind of speed you put on the ball.

WEAVER: You can look at a green and think it may be fast, but sometimes greens are slower than they look or faster than they look.

HICKS: By using the Stimpmeter and the principles of kinematics, golf courses can regulate the speed of their putting greens and give players a consistent way to approach one of the most challenging parts of the game.

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