Understanding simple physics in sports

Physics and sports are inter-connected. Every sports discipline depends on the ability of an athlete in force application, and force is one of the key elements of Newton’s Laws and other fundamental physics concepts.

Physics in sports: Understanding the physics of motion can impact all areas of sports, from helping athletes to move faster, further and higher, injury prevention, programme planning and peaking at the right time.   -  AP

Some of the common terminology we use day today in sport have become a part of the coaching jargon. We will look at some of the examples, their real meaning and how they are being applied in different sports.

A good performance in sports is based on correct control and coordination of movements. Using physics as one of the medium to understand the subject better we will discuss the physics terms used in various sports. For example, knowing the bat speed with which to strike a ball isn’t very useful to a batter, but what is useful is knowing the swing angle to stabilise your wrists so that the bat hits the ball with the greatest speed possible.

Understanding the physics of motion can impact all areas of sports, from helping athletes to move faster, further and higher, injury prevention, programme planning and peaking at the right time.

Physics and sports are inter-connected. Every sports discipline depends on the ability of an athlete in force application, and force is one of the key elements of Newton’s Laws and other fundamental physics concepts.

Along with force, work and energy are among the most important concepts of physics. Both work and energy play an imperative role in sports which is directly proportional to each other — transfer of work and energy from one place to another and from one form to another.

Speed: is the time rate at which an object is moving along a path. Ex: sprinting or chasing a ball or target is a scalar quantity.

Velocity: the rate at which the body is moving in a particular direction. Ex: car moving in a westward direction is a vector quantity.

Acceleration: rate at which velocity changes with time, in terms of both speed and direction. Ex: player running at 10mts/sec towards west, chasing the ball.

Momentum: product of mass of a body and its velocity = mass*velocity.

In contact sports, the more momentum a player has, the more harder it is to stop him or her. Ex: rugby or rules football or basketball players.

Inertia: tendency of an object to continue in the state of rest or of uniform motion. Ex: if you roll a ball, it will be in a rolling motion unless stopped by friction or some force (billiards or soccer ball).

There are three types of inertia — resting, motion and directional.

Angular momentum: the movement of a mass when it is rotating or spinning. A person in a tucked position spins faster than someone in an extended position. In general, the larger the angular momentum of the ball, the larger its linear velocity. Ex: baseball pitching or a fielder throwing a ball to the keeper. This maximises the angular momentum of the throwing arm and of the ball at release.

Deceleration: the rate at which an object slows down. Ex: when we are using brakes during driving, we are taking benefits of deceleration to reduce the speed of the vehicle, especially in stop and go sports.

Torque: is a twisting force that involves the muscles rotational force and measures how much of that twisting force is available when an muscle exerts itself. Ex: fast bowlers’ action or tennis strokes or golf swing. Torque-based gym training is very useful for professional sportsmen — rotating your arms and legs into stable positions before and during movement. Torque is a moment that is applied in such a way that it tends to rotate a body around its axis.

Ground reaction force (GRF): this has three components: its point of application, its magnitude, and its line of action. In the stance phase of normal gait, the point of application progresses along the foot, and the magnitude and the line of action vary through the gait cycle. Ex: while running, the GRF increases up to two or three times the body weight.

Angle of release: ideal projectile motion, which starts and ends at the same height, maximum range is achieved when the firing angle is 45°. If air resistance is taken into consideration, the ideal angle is somewhat less than 45°. Ex: discus, shot put or javelin throws.

Couple: pair of equal parallel forces that are opposite in direction. Ex: steering wheel of a car.

Force: is a push or pull upon an object resulting from the object’s interaction with another object. In sport it can be force creation or force dissipation and can be achieved through various parameters of training the right muscle group. In sport, an internal force is one which is generated within the body. Ex: leg muscles contracting to move the bones. An external force is one that acts outside the body. Ex: a boxer striking an opponent.

In every ball game, a force applied to the ball makes it move, whether from the kick of a footballer or the action of a tennis racquet. In motor sports, force make the vehicles move, and other forces are needed to stop them. Hammer throwers and American footballers make use of force to run and throw.

Levers in the body

First class lever: the fulcrum is in the middle of the effort and the load. Ex: neck flexion and extension

Second class lever: the load is in the middle, between the fulcrum and the effort.. Ex: calf raise

Third class lever: the effort is in the middle, between the fulcrum and the load. Ex: biceps curl.

Newton’s laws

First law: a body continues in a state of rest or uniform velocity unless acted upon by an external force. Ex: a golf ball will remain still unless a force, applied by the golf club, makes it move. Or the same golf ball will continue to move at a constant velocity unless a force acts on it to slow down.

Second law: when a force acts on an object, the rate of change of momentum experienced by the object is proportional to the size of the force and takes place in the direction in which the force acts. Ex: when a golf ball is struck by the golf club, the rate of change of momentum (or velocity) of the ball is proportional to the size of the force acting on it by the club.

Third law: for every action, there is an equal and opposite reaction. Ex: when a tennis player hits a ball, the racquet exerts a force on the ball and the ball exerts an equal and opposite force on the racquet. The racquet exerts the action force and the ball exerts the reaction force which is felt by the player at the time the racquet strikes the ball.

Kinetic energy: when work is done on an object, the object gains speed and acquires kinetic energy. When a player throws a ball, work is done. The arm applies a force to the ball through a distance. Ex: when you hit a ball with a bat or racquet, work is done.

Potential energy: an object can store energy as the result of its position. Ex: the heavy bat is storing energy when it is held at an elevated position. This stored energy of position is referred to as potential energy. Similarly, a drawn bow is able to store energy as the result of its position.

Impulse: it is a certain amount of force you apply for a certain amount of time to cause a change in momentum. Ex: when you hit a ball with a cricket bat, you apply a force for a time (a very short period in this case) to cause a change (or transfer) of momentum in the ball.

Balance and stability: balance is the ability to stay upright or stay in control of body movement, and coordination is the ability to move two or more body parts under control, smoothly and efficiently. There are two types of balance: static and dynamic. balance is established by four different body systems — vestibular system, vision, proprioceptors, and the hip and trunk muscle group. Each can be trained through varied means to achieve the desired results.

Mechanics: mechanics is a branch of physics that is concerned with the description of motion/movement and how force creates motion or movement.

Use of biomechanics is as follows

  • identifies how the muscular and skeletal systems in humans function under various conditions.
  • understands the limits of the human body through various mathematical and physical formulae.
  • improves athletic performance by identifying and applying optimal technique.
  • individualises performance domain.
  • prevents injury and speeds up recovery.
  • increases movement speed.
  • increases power.
  • efficient economy of movement.
  • eliminates muscle imbalances.
  • diminishes wear and tear on joints and ligaments.
  • improves sport and skill specific form and technique.

Drag: every time we move, we have to push millions of air or water molecules out of the way, which slows us down. It can be air or water drag. Depending on the sport, the drag can be form drag, interference drag or skin friction drag. Ex: speed skating or swimming.

Spin: is created by applying a force that is off-centre to the object being thrown (or kicked) at the point of release. The effects of spin are important in all ball sports and throwing events. The magnus effect explains why the paths of balls deviate from normal flight path. Ex: cricket, soccer or golf ball.

Mass: the mass of a body refers to the amount of substance that it is made up of and is measured in kilograms (kg). If a player weighs 100kg, he or she is made up of bones, muscle, fat, connective tissue, etc. Although we talk about a player’s ‘weight’ on scales, weight is a force. If the same player is placed on the moon his/her mass would still be 100kg but the weight would be much less because the gravity is less.

Using the knowledge of physics and other science parameters would vary for different coaches. Understanding the data inference to specific sport and specific athlete and skill to peak at the right time is an art.

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