Thursday, December 30, 2010

The Physics of The Golf Swing

The game of golf revolves around a combination of numerous physics concepts. The effects of physics on the game, which can easily be overlooked, can be found not only during the swing and impact, but they also take effect prior to the swing, while the ball is in flight and after the ball has landed. The physics concepts that will be discussed include, Newton's Laws, acceleration, force, velocity, time, gravity, and angles.

Many things effect the way the ball and its flight including...

~ Lie

~ Weather conditions
* Wind
* Temperature
* Altitude

~ Gravity

~ Angle at which force is applied

~ Newton's Laws

~ Applied Force

Lie - Grass behind the ball will cause, less solid contact between the ball and club, producing less force on the ball. Thus, a ball hit from the fairway may go a couple of yards further than a ball hit from the rough due to the resistance of the grass in the rough. A shot hit from a downhill slope will produce a lower trajectory and a shot hit from an uphill slope will produce a higher projectory.

Weather - The weather plays a large roll in how the golf ball will fly.

~ Wind- The wind plays a large role in both how far the ball will travel and how straight the ball will travel.

Downwind - A shot hit with wind coming from behind will fly farther, have less spin producing more roll and a straighter flight. The shot will go further and straighter and have less spin, the faster the wind is blowing.

Crosswind - A shot hit with wind coming from a side will have a tendency to fly the direction that the wind is blowing. For example, a shot hit with a wind coming from left to right will fly more to the right. The ball will fly the further right, the faster the wind is blowing.

Into the wind - A shot hit when into the wind will not travel as far, will have more spin producing less roll and a less straight flight. The shot will go shorter and will have a tendency to be more off line due to the more spin created by the wind and will not roll as far when it lands. The faster the wind speed, the more all of these effects will be effected.

~ Temperature - The temperature has an effect on distance.

Warm - A shot hit during a warm temperature will go further than a shot hit during a cold temperature. Keeping the force at which the ball and all other factors equal, the ball will go further because the high temperature will cause it to compress more. The more the ball compress's, the further it will go.

Cold - A shot hit during a cold temperature will go shorter than a shot hit during a warm temperature. Keeping all factors equal, the cold temperature will cause the ball to compress less and thus the ball will travel a shorter distance.

~ Altitude - The altitude has an effect on distance. Keeping all factors equal, a ball hit at a higher altitude will go further than a ball hit at a lower altiture. This is due to the less resistance in the atomsphere. The air at higher altitude's is thinner than the air at lower altitude. A golf ball will travel a longer distance at a high altitude because there is less air resistance causing the ball to go further.

Gravity - The effects of gravity on the golf swing, is much like the effects of gravity in everyday life, its effect is often overlooked. Here are a list of numerous ways that gravity effects the game of golf.

~ Without gravity, when the ball is put on the tee it would float, because of gravity (and Newton's First Law, which will be discussed later) the ball stays on the tee.

~ During a player's backswing, they are constantly fighting the effects of gravity. As they lift the club to the top of their backswing they are fighting the -9.8 m/s/s acceleration of gravity which is causing the player to feel as if a force is pulling down on the club as they are trying to lift it up.

~ Tiger Woods, in a golf digest about a year and a half ago, said that one of the things he was trying to feel in his swing was that once the club reached the top of his backswing he wanted to feel as if he let the club and his arms "fall" to begin the downswing. The falling sensation that he said he wanted to feel was due to gravity. He wanted to apply no additional force to the club, only the force of gravity.

~ During the downswing, once the player begins applying force to the club to create acceleration, gravity is also helping the player out. Not only is the players force on the club causing it to accelerate but the 9.8m/s/s acceleration force of gravity is also helping. Since the player's force they are applying is so much greater than the force of gravity, the force of gravity is often overlooked.

~ After the ball is struck the player begins to slow down the velocity of the club. Helping them slow the club down as the club is coming up to the top of their forward swing is the force of gravity. As the club is coming up, gravity is applying of force, causing a sensation for the player as if gravity was pulling down on the club.

~ I have an idea for an info-mercial. It would go something like this "Do YOU want to hit the ball as far as the pros? Well you could, yes anyone could, if there was no gravity!" Ok it is kind of corny but it is true. Gravity is the force the causes the ball to come back to the ground. Without gravity, anybody could hit the ball 300 yards, just as the pros do.

~ Without gravity, Tiger Woods and other pro's would be unable to even hit the ball in the hole. On the putting green, as the ball is putted towards the hole, gravity is the force that causes the ball to fall into the hole.

~ On the putting green, the ball roles and stays on the ground because of gravity. Almost all putters have 5 or 6 degrees of loft. A ball hit with 5 or 6 degrees of loft would fly into the air without gravity. Because of gravity, the ball quickly returns to the surface after being struck.

Angle at which force is applied - This concept can be used to explain why golfer's carry around 14 clubs, and not just one or two. Two balls hit by two clubs with the same mass and same force will vary only due to the angle at which they are hit. A club with 45 degrees of loft will go shorter and will roll less than a ball hit by a club with 25 degrees of loft.

Newton's Laws - What discussion of physics would be complete without mentioning Newton's Laws? Sir Issac Newton's three basic laws all have some effect on the golf swing.

~ 1st Law - The law of inertia. Every object continues in a state of rest, or of motion, in a straight line at constant spped, unless it is compelled to change that state by forces exerted upon it.. Newton's first law serves as an explanation for why the golf ball stays at rest until the player strikes the ball. The only way the ball may move other than due to a strike from the club, is a great amount of wind while the ball is on the putting green. Other than that rare example, the ball will remain at rest until the club hits it. This is a direct example of Newton's First Law.

~ 2nd Law - Acceleration = Net Force/Mass, while force is measured in Newton's and Mass is measured in kg. Now that we have accepted that fact that there is gravity, this is the explanation for why Tiger Woods and other pros hit the ball further than most average players. The pros cause the ball to be hit with more force, using a constant mass, the more force that is applied to the ball, the more acceleration that is created and the further the ball will go. Applied force explained below.

~ 3rd Law - Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object. For the purpose of explanation, let the first object be the golf club and let the second object be the golf ball. Newton's 3rd law states that the force between the club and the ball during contact are equal. As the club hits the ball, it applies force to the ball causing it to go into motion. The ball also applies a force back to the club. This force is less noticable because the mass and acceleration of the club is so much more than that of the golf ball.

Applied Force - There are several equations that factor in the applied force to how far the ball will go.

~ F=MA

~ A= Change in Velocity / Change in Time

With a constance mass, the more acceleration applied during the golf swing, will cause more force applied to the ball during impact causing the ball, when hit at the same angle by the club and launched at the same angle, to travel a longer distance.

When a triple beam balance was used to mreasure the mass of a golf ball, the result was 0.04569 kg and the standard acceleration of a golf club by a professional player is about 100 mph or 44.73 m/s. This speed of the club produces a speed of the golf ball which on average is about 170 mph or 76.08 m/s. The moment of impact lasts for 5 milliseconds which is .005 seconds.

Thus, the equation for the force applied to the golf ball would look like this,

Acceleration = (76.1 m/s) / (.005 seconds)

Acceleration = 15,220 m/s^2

Force = (.04569 kg) x ( 15,220 m/s^2)

Force = 695.4 Newtons

This equation can be used force any swing speed.


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