What’s the single most important factor in golf? That key ingredient separating the best golfers from the rest of us? Depending on who you ask it could be:

• How you grip the club
• How you align yourself at address
• The takeaway and how you initiate the backswing
• The transition between the backswing ending and the downswing beginning
• Maintaining lag during the downswing
• Your state of mind, cultivating a stoic mindfulness whilst playing

And a whole list of other considerations…
They’re all important, yes, but each of those factors only serve to facilitate golf’s #1 element: impact. Nothing else matters. You can get everything else ‘right’, but if impact is poor, then so is your golf.

So what is impact exactly? In The Golfing Machine, Homer Kelley describes it as simply “the meeting of ball and club.” He quantifies a few more features of impact:

• The exact location where the clubface touches the ball is known as the Impact Point
• When the ball leaves the clubface, this is known as Separation
• The period of time between the club first contacting the ball and Separation is know as the Impact Interval(1)

This Impact Interval last approximately 0.0005 seconds.(2) During this incredibly short time, the clubface collides with the ball, causing it to deform and compress. The ball then leaves the clubface, returning to its original size and shape as it flies away. For a driver with a swing speed of 112.5mph during impact, the clubhead exerts 50,000Gs of force on the ball (that’s fifty-thousand times the force of Earth’s gravity) and produces an acceleration of 107,000,000 feet per second squared!(3)

The clubface will impart an initial direction and create spin around a particular axis of the golf ball during the Impact Interval, causing it to fly out on a particular path.(4)

Mr Kelley identified the secret of golf as “sustaining the Line of Compression” during the Impact Interval.(5) This "Line of Compression" is a concept we'll discover in later topics.