The Physics Behind Throwing a Lacrosse Ball- Craig Kelleher

The Physics Behind Throwing a Lacrosse Ball

Craig Kelleher 

Newton's First Law: Inertia

• This law states that an object at rest will remain at rest until acted on by an outside force. In the case of lacrosse, a centripetal force acts on the ball as the player throws it; the balls friction against the mesh keeps the ball in the pocket while the stick accelerates around during a swing. Once the ball is released, it will continue on a straight line with a certain velocity until acted upon by an external force such as another player, the ground, or hopefully the net. 

Newtons Second Law

• Calculating the force of a players throw using Newtons second law: f= ma or force equals mass times acceleration. The centripetal acceleration applied to the ball during the swing determines the force of the pass, because the mass remains constant throughout the process. 

Newtons Third Law

• This law states that for every reaction, there is an equal and opposite reaction. So, when throwing a lacrosse ball, the stretch in the mesh pocket and the motion of the ball counteracts the force put into swinging the stick. The ball is forced forward as a reaction the the swinging of the stick. Another example of this is when the ball accelerates out of the stick and hits the back of the net. The force applied to the ball is then transferred to the force required to move the net, in order to determine the shot was a goal. 

Torque and Lever 

• When examining the physics of a pass, the lever arm created is important for building the correct throwing motion. In order to throw the ball from the mesh pocket, one must pull the stick backward with the bottom hand and push it forward with the upper hand. This simple motion creates a lever that accelerates the ball forward with centripetal force you have swung the stick. This motion also creates torque that is used to send the ball small or large distances.   

More about angular velocities 

• A force is required to begin and or stop and objects rotation, just like motion in general, objects at rest tend to stay in that state and the same goes for objects in motion. We know a force is required to start or alter and objects rotation. There are several important factors when looking at a certain force to see how much rotation or lack of rotation it will cause. An equal force acted closer to the axis of rotation will have less of an affect than that same force when acted further from the rotation. The force that causes a change in rotational acceleration is defined as torque or the greek letter for “t”. It is directly proportional to angular acceleration. Angular acceleration is the acceleration of an objects angular velocity or how many degrees it rotates per unit of time. This relationship can be defined as: Sum of all torque force is proportional to angular acceleration, assuming that the mass is 1. This is taken from the original Newton equation F=ma. Force in this case is the sum of all torque and a is the angular acceleration.

Continued.... 

• The general equation for angular velocity is w=d*theta/dt. This means that w, the angular velocity is defined as the change in angle over the change in time. So that is the equation for the angular velocity. What is important to understand is how a torque force results in angular velocity. Think of torque as the angular equivalent of F.  F=ma and the torque force = the mass of the object rotating times the angular acceleration the force. So the torque created by a lacrosse player using the friction of the earth to rotate his hips, chest, and shoulders to shoot the ball translates up the stick into the ball itself giving it a angular acceleration, until it eventually overcomes the friction it experiences while resting in the lacrosse head. It then releases into the air. 
  

More about Torque and Lever Arm principles

• The general idea of a lever arm is to maximize the ratio of input force to output force. If a force is acted on the beam further from the pivot point it will cause more motion than if it was closer because the linear velocity of an object is larger the greater the radius of portion is. It can be a fixed beam, jointed, or bent rod-like structure and still create leverage. This is the principle that proves the common belief that in lacrosse it is important to extend your hands. Extending the hands makes the radius of rotation larger. 

• I discovered that the main principal involved when talking about the release of a shot is that of torque and the lever arm. This is a general term for when an object is acting on by a force with a distance from the original placement. In this case, it applies because there is a distance between the center of the lacrosse ball’s mass and the axis of the rotation, which is assumed to be the center of the chest in this case. Torque is the amount of force that causes an object to rotate about a pivot point. This applies directly because the torque value will be the force that rotates the stick which will eventually release the ball. This is a term commonly heard with relation to a vehicle’s engine and is a good measurement of the car’s performance.