CBSE Class 12 Physical Education Biomechanics And Sports Notes Set 03

Biomechanics and Sports

Biomechanics is the branch of Kinesiology which deals with the precise information of human movements using scientific methods. It is the application of mechanical principles in the study of living organisms so as to prevent injuries and train physical movements.

Newton's Laws of Motion and their Application in Sports

Laws of Motion

Sir Issac Newton made three laws of motion which are explained below

• (i) Newton's First Law of Motion: This law is also known as law of inertia. This law states that a body at rest will remain at rest and a body in motion will remain in motion at the same speed and in the same direction till any external force is applied on it to change that state.
• (ii) Newton's Second Law of Motion: This law states that the rate of change of momentum of an object is directly proportional to the force producing it.
  \( a = \frac{F}{m} \) where \( a \propto F \), \( a \propto \frac{1}{m} \)
• (iii) Newton's Third Law of Motion: This law states that to every action, there is always an equal and opposite reaction. This law describes what happens to a body when it exerts a force on another body. These three laws are still being used to this day to describe the kinds of objects and speeds that we encounter in everyday life.

Application of Laws of Motion in Sports

First Law

• (i) Softball: The ball is hit into the air. Eventually, gravity will act on the ball, pulling it down to the ground. Then, it will roll until friction between the ball and the grass stops it.
• (ii) Soccer: When a soccer ball is kicked into the air, gravity will pull it back to the ground. Then, it will continue to roll until friction between the ball and the grass slows it down.
• (iii) Dance: When a dancer leaps, he/she only stays in the air for a short amount of time because air resistance and gravity works against them.
• (iv) Basketball: When a basketball is shot, it takes a parabolic path due to gravity acting on it. Then it slows down due to air resistance and fluid friction.

Second Law

If a baseball player hits a ball with double the force, the rate at which the ball will accelerate (speed up) will be doubled. Football players can slow down, stop or reverse the direction of other players depending upon how much force they can generate and in which direction.

Third Law

A swimmer propels herself through the water because the water offers enough counterforce to oppose the action of her hands pushing, allowing her to move. An athlete can jump higher off a solid surface because it opposes his body with as much force as he is able to generate, in contrast to sand or other unstable surface.

Equilibrium

Equilibrium can be defined as a state of balance among forces acting within or upon a body. In other words, it is a state in which all influences, forces are cancelled or counterbalanced by each other i.e. the sum of all opposite forces acting on it is zero. Thus, it is a scientific term describing balance and stability.

In the human body, a state of equilibrium occurs when its centre of gravity lies over the base and the gravity line falls within the base of the body. The greater the body surface in contact with the ground, the larger is the base of support. Hence, the posture of sitting is more stable, easier and more comfortable than the posture of standing.

There are two types of equilibrium

• 1. Dynamic Equilibrium: It is a state of balance of all applied forces acting on a moving body.
  In simple words, when the moving body is stable and balanced such that it results in movement with unchanging speed and direction, then the body is said to be in dynamic equilibrium.
  For instance, when a sportsperson is running, or taking part in gymnastics.
• 2. Static Equilibrium: It is a state of balance that occurs when the body is at rest or in a motionless position, i.e. when the centre of gravity is in a static position.
  For instance, standing on one leg, sitting on a chair, etc.

Centre of Gravity

The balance and stability of an individual depends upon the centre of gravity. Centre of gravity of a body is an imaginary point around which the body of the object is balanced. In human being, the centre of gravity can simply be considered as the centre of weight of the body.

The weight of the body is just the sum of individual weights of its components like arms, legs etc. The centre of gravity has the property of continuously changing during movement. The centre of gravity depends on the shape and size of the body. If a body has more mass distributed in its upper part, the centre of gravity will be towards the top of the body. Centre of gravity always changes its direction according to movement.

For instance, a basketball player, while jumping up to score a basket, swings both arms upward and forward to raise his centre of gravity and thus reach the maximum height. But once in the air, the player drops one arm to his side and tries to reach the maximum with the other arm to score a basket. This reduces his centre of gravity, so that he does not become unstable.

Applications of Centre of Gravity in Sports

The knowledge of equilibrium and centre of gravity are essential for sports and physical education. The ability of balance whether in stationary position or in movement, is a key to success in most of sports and physical activities.

Proper application of the concepts in sports can improve performance. This can be done by following the methods given below

• A sportsperson can become more stable by lowering his/her centre of gravity.
• To maintain balance during a performance, the sports person must ensure that the centre of gravity remains over and nearer his support base. When the centre of gravity is beyond the base, balance is lost.
• For rapid movement of his body from a position of readiness, the sportsperson should position his body so that his centre of gravity has to move the minimum distance to clear the support base. This is particularly applicable during the start of sprint races.
• Shifting the centre of gravity towards an approaching force increases the sportsperson’s ability to maintain balance.

When lifting or carrying an object, shift the body weight in order to maintain balance.

Friction and Sports

The force acting along two surfaces in contact which opposes the motion of one body over the other is called the force of friction.

Friction is of two types

• (i) Static Friction: The opposing force that comes into play when one body tends to move over the another surface but the actual motion has yet not started is called static friction.
• (ii) Dynamic Friction: It is the friction between two surfaces that are in relative motion with respect to each other. It is the opposing force that comes into play when one body is actually moving over the surface of another body.

Methods of Reducing Friction

• (i) Polishing: By polishing the surfaces in contact, they become smooth and the force of friction reduces. Many implements like the discus are painted to reduce friction.
• (ii) Lubrication: The lubrication of surfaces makes them slippery and this reduces the force of friction.
• (iii) Streamlining: Friction due to air is reduced by streamlining the shape of the body. The aeroplanes are made with a sharp front to reduce friction.
• (iv) Use of Ball Bearings: Ball bearings are used to reduce the force of friction.

Many sports require more friction and other need lesser friction. For instance, in athletics, the shoes are designed to increase friction so that better speed can be generated. This is accomplished by fixing spikes on the bottom of the athletes' shoes.

Friction in Sports

It is important to understand the role of friction in sports to bring efficiency in playing that sport. Friction is also called a necessary evil. It may hamper performance in certain sports like cycling, roller skating, skiing etc.

If the friction is more, then the cyclist will have to put more effort to cycle. If there is less friction between the road and tyres, then it will become too slippery and the cyclist may fall. Athletes, footballers, hockey players and sprinters, prefer to wear studs (shoes with spikes) to have proper friction that helps them in running fast without slipping.

Likewise, sportsperson performing various sports like weightlifting and gymnastics like to pad their palms with lime powder for better grip of the horizontal bars. Badminton, squash players who need to hold the racket firmly also use gripping tapes to manage friction.

Projectile in Sports

A projectile is anything which is thrown or jumped into the air. Once it has left the ground it will follow a flight path called a parabola until it once more comes back down to earth. This applies to balls, javelins, discus, long jumpers, high jumpers, and horses show jumping.

An object must be dropped from a height, thrown vertically upwards or thrown at an angle to be considered a projectile. The path followed by a projectile is known as a trajectory.

If gravity were not present, a projectile would travel in a constant straight line. However, the presence of gravity forces projectiles to travel in a parabolic trajectory, thus gravity accelerates objects downwards.

Factors Affecting the Trajectory

Factors affecting the trajectory are as follows

• Angle of projection
• Projection velocity
• Relative height of projection

In order to analyse projectile motion, it is divided into two components, horizontal motion and vertical motion. Perpendicular components of motion are independent of each other i.e. the horizontal and vertical motions of a projectile are independent. Horizontal motion of an object has no external forces acting upon it (with the exception of air resistance but this is generally not accounted for).

Due to this absence of horizontal forces, a projectile remains in motion with a constant horizontal velocity, covering equal distances over equal periods in time. Thus no horizontal acceleration is occurring. The degree of vertical velocity however, is reduced by the effect of gravity.

Force of gravity acts on the initial vertical velocity of the javelin, reducing the velocity until it equals zero. A vertical velocity of zero represents the apex of the trajectory, meaning that the projectile has reached its max height. During the downward flight of the projectile, vertical velocity increases due to the effect of gravity.