# Golf Physics

After leaving the club face, does a golf ball immediately begin to decellerate?

Off my club face? Yes. It also tries to go around the world to the left. It would make it, too, if it weren’t for the automatic water-find feature.

Livin’ on Tums, Vitamin E and Rogaine

Yes.

Once the ball leaves the club face the only forces acting on it are aerodynamic. The primary aerodynamic force is drag which (duh!) decelerates the ball. I guess it is just possible that the backspin (which does generate lift) could generate a force that could accelerate the ball slightly (trading rotational kinetic energy for linear kinetic energy).

## I don’t believe this force could be larger than the drag, however. Additional aerodynamic forces, like lift or this possible accelerating force, also increase the drag. The idea (with lift) is to trade speed for height to make the ball go farther by rising more.

“No wonder of it. Sheer plod makes plough down sillion shine.”
Gerard Manley Hopkins

manhattan, I just noticed your sig and I just need to comment on how great it is!

Yes. Initially, the forces on the ball are: air resistance, which acts opposite to the direction of motion, gravity, which acts down (which has a component opposite to the direction of motion while the ball is rising), and lift due largely to spin, which may be in any direction (roughly) perpendicular to the direction of motion. All these forces act to either change the direction of flight or to slow the ball down. There is no force acting in the direction of motion to speed the ball up (or to maintain the speed against air resistance). After it reaches the top of its trajectory, the ball is accelerated (partially) in the direction of motion, so it might be going faster when it lands than during the middle stages of its flight–but still not as fast as it was going when it was hit.

On second thought, any aero people out there who know if there is a mechanism for transferring rotational energy to kinetic energy of the center of mass of the ball? That might provide a way for in-flight acceleration.

Rick

Darn. Pluto beat me to it. And answered better. Kudos (not the granola snack) to you.

Rick

Actually, there is. When the ball is struck, it compresses against the clubface. The energy released as the ball returns to it’s original shape adds to the initial acceleration. A good pro golfer can manage a clubhead speed of ~120 MPH. The initial velocity of the golfball, however, is much greater (275 feet/sec, or 15000 feet/min).

The overwhelming majority of people have more than the average (mean) number of legs. – E. Grebenik

Doc,

I’m pretty sure that the compression of the ball only contributes to the ball’s acceleration while it is in contact with the club face. Once it leaves the club face any recoil from the ball compression will actually have decelerative effects (if any).

I think Manhattan and I should pair for golfing tournaments. Mine go around the world to the right, except for the automatic backyard find feature… (sigh).

Course, maybe that is cause MY golfballs follow the right hand rule… < ducking >

I don’t know golf, but I do know physics, so somebody tell me if I’m making any mistakes here:

After the ball is no longer in contact with the club, there are three possiblities: (1) It starts out going up, and will come down after reaching its maximum altitude. (2) It is going down, and will not get more than a few feet horizontally before reaching the ground. (3)It may be going exactly horizontal, but only for the first instant, after which it will go down.

Swings resulting in type 2 or type 3 motion are very embarrasing and can be ignored for this question, which most certainly concerned a type 1 swing.

Okay, so we are now looking at a golf ball which is moving horizontally at a gread speed, fighting wind resistance. It is also moving upwards somewhat, fighting gravity. It may also be spinning, which at the very most will cut down the wind resistance and provide some lift, neither of which do anything to increase the welocity of the ball.

Someone thinks that this ball won’t immediately decelerate even after the club is not pushing it any more? Sounds to me like someone has dreamt himself a nifty perpetual motion machine!

Keeves, what I was saying was that the “de-compression” (Oh, crap! What is the word I’m looking for?)of the ball will cause some acceleration after the ball leaves the clubface. Put a balloon on the floor. Push the balloon down with your hand (compress it). Quickly remove your hand. What happens? The balloon accelerates enough to leave the floor. If that concept does not apply to a golf ball/club face, let me know why.

The overwhelming majority of people have more than the average (mean) number of legs. – E. Grebenik

Doctor,

The golf ball does rebound from the club face, but the rebound force stops as soon as the club and the ball separate. At that point the ball may still be recovering its original shape but it is no longer pushing on anything (other than air) so the elastic oscillation of the golf ball itself doesn’t affect the linear motion.

The example of the balloon is similar – you compress the balloon and let it go. It rebounds and pushes itself upward from the floor. But, again, as soon as the balloon is no longer touching the floor it can’t exert any upward force by pushing against the floor. It does have some upward velocity and its momentum will carry it up, but it is no longer accelerating upward.

“The departure of the church-going element had induced a more humanitarian atmosphere.”
Dorothy L. Sayers
Clouds of Witness

Gotcha. Duh. That’ll teach a banker/golfer to attempt to deal in physics.

Banker/Golfer: Now there’s a strange combination.