Using the ground

I keep reading about how you should "use the ground" in your golf swing. However, I have never  quite  understood what this means.

To my knowledge I have never heard any instructor explain this concept. I aM SUSPICIOUS  that   it means something like

"remain in  dynamic balance' ( whatever that  means).

Does using the ground  mean your head should  jump up and down during the swing.?  That YOUR  feet should  push  laterally  or resist pushing laterally?  That you  should  flex your knees on the backswing and extend them on the downswing or follow thru?  I note some players heads  go down on the backswing and up thru the downswing. Some players heads go down  during the transition and up through the follow through. Some players heads stay put during the swing. It seems to me that  if you are addressing the ball you are certainly using the ground as opposed to trying to  hit  the ball after jumping up in the air. What gives?

As I see it, there are two primary ways to use the ground. First is as simply a support base helping to correctly position and balance the turning of the torso and delivery of the club. Second is as a source of energy -  as a platform against which your muscles can work (along the lines of someone bracing to pull-start a gas lawn mower). Some energy comes from vertical movement of your mass, some from lateral movement, and some from using that platform to transfer muscular work against that base into rotational force / torques through the kinetic chain (braced legs help turn hips, moving hips help turn shoulders, moving shoulders turn arms, arms deliver 'lagged' club). As the distance to the pin gets short the energy element is typically lessened in favor of accurately positioning the movement of the upper torso.

This thread has some good stuff related to your question: http://thesandtrap.com/t/41932/ground-reactive-forces-and-jumping-for-power

This aspect of using the ground in the thread above is akin to the movement you would do if you were trying to jump high. There is always a little 'dip' of your center of mass toward the ground to 'load' the thighs, glutes, and achilles tendon (a squatting motion), initiating stretch-shorten cycles followed by active muscular contraction of the big muscles to 'launch' the body up. Rather than moving the body mass as high as possible (and too far from the ball), the golf goal is to use a more controlled motion to extend / straighten the left side (and lift the left shoulder) which helps whip the club through impact. If you are as athletic as Lexi Thompson or Bubba Watson, you might try for both heels off the ground around impact, but I expect there's a tradeoff with consistency vs getting the left leg mostly straight and the left shoulder high.

Fair enough. I get where you are coming from. I should have used quotes around 'source'. Platform is more precise.

That said, gravity (originating below the ground surface) can aid in accelerating the club on the downswing. A compression into the ground (COM - c/g drop) in transition / early downswing - for those who use it - doesn't just load the big muscles it also helps load the shaft at the top and bring it down to delivery. With the whole mass of the body accelerating with a (very short) 'free fall' in that phase it's not the biggest force in the swing, but not insignificant IMO. That's more the line I was thinking about when I used 'source'...gravity ('in the ground') can be a source of energy if you use vertical torso movement...like the drop of a trebuchet counterweight.

Agreed the 'platform' is the more important / significant element to using the ground.

I would say that the clubhead position in the swing can effect how the body feels it, and maybe in some instances help in the movement of the club to a better swing path. Example of the clubhead is too inside it must be rerouted upward, which is going against gravity.

Yet still the physics behind gravity is based on mass. In the end the effect of gravity on an object is based on its mass. In the golf swing that primarily is the clubhead. Yet the clubhead is still only 200 grams or so.

Just for fun, lets assume we are at sea level and you want to compare the actual gravitational force from the earth onto the golf club compared to lets say a 70 kg (154) lb person.

The interaction between a golf club and the earth only produces about 1.96 N. The interaction between the earth and the 70 kg man is 686 N. The gravitational force interacting on the human body is 350 times as much as it does on a golf club head.

I would say that the effect gravity has compared to that the muscles apply to the golf club is minimal at best.

Even if you don't compress down with your COM gravity adds about 8% to club speed at impact, according to some very knowledgeable folks who model the swing. I think that's significant and not negligible , but clearly not predominant / primary .

On earth, I expect a compression move also adds a bit (much smaller due to the time and distance than 8%) of acceleration on the downswing. But I think it primarily helps position and load the big leg muscles for the left side jump / extension, which is why I agree the 'platform' aspect of the ground is much more important for power. I think it can also aid (but isn't essential) in forming lag. For actual swing mechanics, I agree thinking about gravity is insignificant (except possibly for 'high hands' at the top) because every real-world golf swing gets the 'free ride', even bad ones like mine. Just aiming to be precise in descriptions / whole picture.

On the moon, I expect someone who really compresses into the ground on the downswing like Nicklaus, Rory, Tiger, Bubba, & Lexi, would actually get a little spaceborne through impact, which might inhibit good contact. If you could swing without a spacesuit restricting you, then you might be able to swing 'pretty much the same speed', but you'd definitely lose a bit from the weaker gravity. I also think that the lower gravity would affect how much force you could effectively apply against the 'platform' with your muscles without throwing you out of position, which could really slow swing speed. I think you should rent some time on NASA's 'vomit comet' to test my theories. It's probably cheap - at least relative to mounting your own moon mission. Or we could get the golf team from an engineering school to sponsor an experiment: https://engineering.purdue.edu/hirl/projects/nasa2003_iflyvomitcomet/nasa-experiment-details.htm. Some YouTube vids of this would be good both for generating interest in STEM and golf!

You can ignore the tides all you want, but I score .0000005 shots lower when the moon is in the 7th House.