# The physics of the golf swing

I realize this is sports related, but I have a very specific question that I hope our physics mavens can help me with. If the mods take exception, so be it.

In golf, it is known and taught that a slice reduces distance and a draw adds distance. The draw supposedly adds roll, I think, among other things. And that has certainly been my experience, so I’m not questioning the advice so much as asking why?

A slice is typically an “outside to in” swing path, where outside means farther away from the golfer and beyond the target line, with an open club face (meaning, the toe of the club trails the heel of the club). A draw is the opposite.

It seems to me the ball doesn’t know what I’m aiming at; it should be all about the swing path and how square the club face is. Worded differently, shouldn’t a slice or fade swing be the same as a draw swing of the same velocity from a left handed golfer?

But damned if the long, LONG established wisdom isn’t right. Slices and fades rob distance, and draws seem to roll forever.

What gives? What are the physics that explain this?

Human joints. A slice swing restricts joint movement and reduces power.

How so? A slice swing of the same velocity doesn’t travel as far as a draw. Or if not, a hundred years of golf wisdom is wrong, which I suppose is possible.

Also, that doesn’t explain why draws roll further after landing. And they certainly seem to.

Are you sure you’re getting the same velocity?

With my swing, nothing is sure. But I’ve seen analytics from pros where swing speed is virtually identical. And pros definitely use fades for control, knowing they sacrifice distance. IOW, a fade stops real close to where it lands.

Or as Lee Trevino used to say, you can talk to a fade, but a draw doesn’t listen.

A golf swing is inherently asymmetrical since you are doing it to one side of your body.

Slice involves putting clockwise (when viewed from above) spin on the ball. Draw involves putting anticlockwise spin on the ball.

Top spin will make the ball roll further while backspin has the opposite affect.

It’s a bit hard to explain but try the hand movements yourself. For a right-hander, it is exceedingly awkward to attempt to put top spin and clockwise spin on the ball. It is similarly awkward to put backspin and anticlockwise spin on the ball. Both involve unnatural and possibly almost impossible movements when your arms are swinging around the right hand side of your body.

Very similar to controlling the balls in snooker or pool I think

As you noted, a slice has an open club face, and a draw has a closed club face. With the geometry of the club, how you hold the club, and how you generate an open/closed face, the open face will have a higher apparent loft than the closed face. Higher loft, lower distance and less roll, lower loft is the opposite.

I do not have the answer, but wanted to add that one time I took out from the library a book on the physical of gold. Possibly this book.

I have been a longtime avid golfer and I enjoy reading abut golf and science, so I thought it would be interesting. Well, from the get go, the book was talking about compound levers and moments of inertia at a level that made e toss it aside more quickly than I abandoned A Brief History of Time.

I would bet that book - or similar books and articles - will have the answer you seek. I’m just not confident you would be able to understand it!

Assuming you’re talking about spinning the ball, spin reduces distance in two ways. First, with the initial hit, energy is going into translational motion and spin motion. More energy in the spin motion means less energy in the translational motion.

Second, the spin affects the trajectory by exchanging energy with the fluid it’s moving through. Some of that exchange add distance to the trajectory, depending on which way the winds are blowing. But most of the exchange is removing energy from the ball and giving it to the fluid. That reduces the distance.

The spin can also increase distance. The spin adds stability to the ball with a gyroscopic effect similar to a rifled bullet. And the spin also trades some forward energy for lift.

Thanks for the responses. I think @Cheesesteak and @Princhester have got it. I need to think about.

It makes sense that a draw reduces the loft of the club. That by itself means that backspin is reduced (I don’t think it’s ever eliminated, except maybe with a driver), as well as giving distance just because of the lesser loft.

Yes I believe that a slice imparts more backspin than does a draw, so there’s less roll with the slice for swings of equal energy.

Why do dimpled balls go further than smooth ones?

The dimples reduce aerodynamic drag. Here’s a oversimplified explanation why:

Airflow over an object can be (in order of least to most drag) laminar, turbulent or separated. A smooth ball would have a small area of laminar flow on its leading face which would turn briefly turbulent, then fully separated not much further than halfway back. The dimpled ball forgoes the small amount of laminar flow, but features turbulent flow (generated by the dimples) most of the way back, thus enjoying a substantial reduction in total drag.

And tennis? But in that case, a lot of the control is how the ball bites the ground on the first bounce, not the aerodynamics in flight.

As for dimples, they were added because apparently smooth balls in the olden days tended to meander in their flight path depending on vagarities of the aerodynamic turbulence they generated. Just like bullets from an unrifled firearm were highly inaccurate.