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Flexion is a decrease in the angle between two adjacent segments in the body as the ventral surface of the segments approximate each other. It occurs in a sagital plane about a frontal axis.

The following factors affect the trajectory:

(a) Angle of projection: When the angle of projection is 150, the maximum horizontal distance is achieved. 

(b) Initial velocity: The horizontal range also depends on the amount of initial velocity. Greater the initial velocity applied on projectile at the time of release, greater horizontal distance is achieved. 

(c) Gravity: particularly in throwing events. when an object is thrown in air it is left to fall freely under gravitational force. At the surface of the earth its value is 9.8 metres. Its value changes at different places. At high altitude its value decreases and results in better distance in jumping. 

(d) Air resistance: Air resistance plays an important role in many sports in which balls or other objects are thrown in air. The speed slows down by air resistance. If the surface of projectile is rough, it will increase friction and will certainly affect the horizontal distance.

Centripetal Force: A force required to make a body move along a circular path with uniform speed is called centripetal force. It always acts along the radius and torwards the centre of the circular path. When a body is in uniform circular motion, its velocity changes continuously due to change in direction of motion.

F_C = mv²/r

When a person walks he pushes the ground or earth backward with his foot. The tendency of the foot when it is in contact of the earth is to move backward. Hence the force of friction acts in the forward direction, i.e.. in a direction in which the man walks.

(a) Dorsal - towards the spine. 

(b) Ventral - towards the sternum. 

(c) Medial - towards centre line. 

(d) Lateral - away from centre line. 

(e) Cranial - towards the head. 

(f) Caudal - towards the tail. 

(g) Rostral - towards the nose (beak). 

(h) Proximal - towards the body (trunk). 

(i) Distal - Away from the body.

Anatomical plan - Perpendicular Axis

(a) sagital (media) - Horizontal (medio-lateral)

(b) frontal (coronal) - Antero-posterior (sagital)

(c) transverse (Horizontal) - Longitudinal (vertical)

Mechanical energy is the energy associated with a body due to its position, configuration or motion. It is associated with a body of two types: namely kinetic energy by virtue of its motion and potential energy by virtue of its position or configuration. The total mechanical energy of a body (E) is the sum of its potential energy (U) and Kinetic energy (T). i.e., E = U + T

The force that arises in response to an attempt to slide or roll an object on another is called friction. It always opposes the relative motion between any two surfaces in contact.

Extension is an increase in the angle between two adjacent segments in the body as the ventral surfaces of the Segments move away from each other. It occurs in a sagital plane about a frontal axis. An exception is extension of the thumb. which takes place in a frontal plane above a sagital Axis.

An athlete runs for a certain distance before taking long jump so that inertia of motion gained by him at the time of jumping adds to his muscular effort and helps him in taking a longer jump.

Due to its small mass, the momentum of the table tennis ball is much smaller than that of cricket ball moving with same velocity. Less force is required to stop the table tennis ball than the cricket ball. Hence, it is easier to catch the table tennis ball than the cricket ball.

The impulse is equal to the product of the force exerted by the ball and the time to catch. By lowering the hands, the time to catch increases. Then the force exerted on the hands becomes much smaller and it does not hurt the cricketer.

In boxing or Karate, we need powerful punches that are delivered at a great speed.

Extension - Increasing the angle of a joint. 

Flexion - Decreasing the angle of a joint. 

Abduction - Movement away from the body. 

Adduction - Movement towards the body. 

Pronate - Rotation of the limb to move the dorsal manus medially. 

Supinate - Rotation of the limb to move the dorsal manus laterally.

It is the surface on which the movement occurs or takes place.

The word 'work' refers to any kind of physical activity. Work is said to be done when force acting on a body displaces it. In simple terms we can say that work is said to be done only when a force produces motion. e.g., pulling a table, cycling, lifting a bag, etc.

Energy can he defined as the capacity or ability of the body to do work. Work is always done at the expense of energy. In other words, energy is spent when a force does work on an object. The SI unit of energy is Joule and in cgs system erg.

Energy refers to the total amount of work a body can do, power determines the rate of doing work. Thus, in power, time taken to complete the work is significant. But in energy, time is irrelevant.

If we roll a ball along the ground, we notice that it slows down and stops even though no apparent force is being applied to it. The ball slows down and stops because of friction. Friction is resistance to motion.

Walking: 

(a) There is double support phase. 

(b) The force exerted on the ground during walking is less. (i.e., less propulsive force) 

(c) Contact with ground remains throughout. 

(d) Stance phase duration is longer in walking. 

Running: 

(c) There is flight or double swing phase during running. 

(b) The force exerted on the ground during running increases or (more propulsive force) 

(c) The body is totally airborne for a period of time. 

(d) Swing phase duration is longer in running. 

Force is a push or pull, which tends to change a body's state of rest or motion. It tries to stop or stops a moving body. It also changes or tries to change the direction of motion of the body. It is measured in Newton and is denoted by N.

As the applied force increases, the static friction also increases and becomes equal to the applied force. This is why static friction is called self-adjusting force.

Mechanical analysis of Running: Running is achieved from a series of alternating hops from left to right leg. The ankle, knee and hip provide almost all the propulsive forces during running. Running has alternate periods of single step separated by flight phase when both feet are airborne. It has the following phases. 

(a) Stance: 

(i) Initial contact: The first contact of the foot is made by heel. It continues till the whole sole of the foot comes into contact with the ground. The knee and ankle flexes and the foot roils in to absorb impact forces. 

(ii) Mid-stance: In this stage sole of the foot completely touches the ground. At this point whole body balances on one legs. 

(iii) Propulsion: The supporting leg leaves the ground therefore the opposite leg comes into contact with the ground. 

(b) Swing: The non-supporting leg swings past stationary leg and becomes ready for the next step. The swing ends with initial contact. 

Upper body and arm mechanics during running: Its main function is to provide balance and promote efficient movement. The movement of arms should be opposite to the legs. Arms movement adds to gain momentum.

Abduction and Adduction are the movements in frontal plane about the sagital axis. These involve moving of the body part away or towards an imaginary centre line. Abduction is taking the body part away from the central line and adduction is moving it towards it. Adduction can also be moving the body part across the centre line and to the other side of the body. Among the joints capable of abduction and adduction are shoulder and hip joints.

Momentum: The effect of motion of a body depend both on its mass and velocity. The product of mass and velocity of a body is called its momentum. It is the quantity of motion possessed by the body. 

Momentum = Mass x Velocity, P = mv

Momentum is a vector quantity because the velocity V is a vector quantity and mass m is a scalar quantity. Its direction is same as the direction of the velocity of the body.

Friction: The force acting along two surfaces in contact which opposes the motion of one body over the other is called the force of friction. Larger the area of contact between the surfaces, greater is the force of friction. When both the surfaces are smooth, the force of friction reduces to almost zero.

The three laws of motions are: 

(a) Newton's first law of motion: This law is also called 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. 

(b) Newton's second law of motion: It states that the rate of change in linear momentum of an object is directly proportional to the force producing it. 

(c) Newton's third law: This law states that to every action there is always an equal and opposite reaction.

Due to friction we are able to push the ground backward during walking. The reaction of the ground helps us to move forward.

When a body slides on the surface of another body, the frictional force exerted by the surface is called the sliding friction. Example: The resistive force encountered while sliding a table over a smooth floor. After the body just starts to slide on a surface (external force exceeds the limiting force of static friction), the force required to maintain the motion of the body over the other surface with a uniform velocity is a measure of dynamic or sliding friction. 

The frictional force that exist between two surfaces when there is a relative motion between them is called dynamic or sliding friction. Another example is sliding over ice.

Static Friction: When a body in contact with a surface is at rest and no external force is applied on it. the force of friction on the body is zero. But when yon apply a force of less magnitude on the body horizontally, the body continues to be at rest due to the force of friction which acts tangential to the surface of contact, in a direction opposite to the direction of force applied. So, the friction offered by the surface keeps the object on it stationary. Although the object is not moving on the surface. it has a tendency to move due to the applied force. The friction in such case is called static friction. So, the static frictional force is a self-adjusting force which increases on increasing the applied force till the relative motion just starts. e.g. a boy standing on ice. 

Rolling Friction: When a body rolls on the surface of another, the frictional force exerted by the surface on the rolling body is called rolling friction. e.g. Friction exists between rolling tyre and the road. The motion of the wheels is called rolling motion and force of friction exerted by the surface is called rolling friction.

The main reason for friction is the roughness of the surface. When we see the surface of an object, it may appear smooth. but when we see it through a microscope. the magnified image will show a number of' tiny hills and valleys.

When an object tends to slide over another, interlocking of hills and valleys resist the relative motion and creates the force of friction. Smoothening the surface reduces friction. But if the surfaces become very smooth and flat, the friction from the molecular attraction becomes significant.

Friction is both helpful as well as harmful: 

Friction is Necessary: It reduces the efficiency of work done. Nothing would be able to move without friction. Friction is how things accelerate. Without friction we would not be able to walk, we would just be slipping. Without friction we can not give better performance in sports. Examples: athletes use spikes and footballers use studs to have appropriate friction while they run fast.

A Gymnast uses lime powder on his/her palms to perform many activities like horizontal bar, uneven bar, Roman Rings. In Badminton, players are usually seen to rub their sole of shoes with lime before going to tlhe wooden court. It is done to provide better grip on the floor so that one can move safely. Kabaddi players rub their hands with soil for a better grip of the opponent. 

Friction is an evil: It is an evil because it results in energy wastage. Due to friction we have to spend lot of energy and money to make things move and make life move on. Wear and tear happens because of friction. In cycling, there should not be more friction between the road and tyre of cycle. If there is more friction, there will be more energy wastage of the rider. In cycle and motor mechanics we use grease to reduce friction to increase efficiency. In roller skating there should be less friction for better performance. 

Therefore friction is both a friend and a foe. 

Three basic reference planes are used in Anatomy: They are: 

(a) Sagital plane: It is perpendicular to the ground and divides the body into left and right. The medial plane is in the midline i.e.,it would pass through the midline structures (e.g. navel or spine), and other sagital planes are parallel to it. 

(b) Coronal or frontal plane: It is perpendicular to the ground and divides the body into dorsal (posterior) and Ventral (anterior) portions. 

(c) Transverse plane: It is also known as axial plane or cross section, divides the body into cranial (head) and caudal (tail) portions. It is parallel to the ground, which separates the superior from the inferior.

The force of friction is of three kinds. 

(a) Static friction 

(b) Dynamic or sliding friction/Kinetic 

(c) Rolling friction

The optimum projectile angle for achieving maximum horizontal range in throwing events is considerably less than 45^o. This is because an athlete can generate a greater projection velocity at low projectile angle than at high angles. The range of projectile is strongly dependent on projectile speed. In sports, the fact is that the projection speed of implement decreases when you throw within the higher projection angle. Shot put has a projectile angle from 26^o to 42^o. Every athlete has a unique speed, angle curve that depends on his/her stature, strength and throwing technique. 

The flight of discus is greatly affected by aerodynamic forces acting upon it. The aerodynamic forces come from the movement of the discus through the air. When in flight, the discus is affected by force of gravity, aerodynamic lift and aerodynamic drag. The stability of discus flight comes from the spin of the discus. Discus has a projectile angle from 27^o- 43^o for maximum range. To achieve maximum distance in Javelin the athlete will have to balance three components-speed, strength and technique. After approach - run of 13 - 17 strides the releasing angle for Javelin has to take into consideration aerodynamic lift and drag. Distance achieved in Javelin depends upon height of release, angle of release and speed of release of Javelin. The optimum angle of releases 26^o to 40^o.

An axis is a straight line around which an object rotates. Movement at the joint takes place in a plane about an axis. There are three axis of rotation: 

(a) Sagital axis: Passes horizontally from posterior to anterior and is formed by the intersection of the sagital and transverse planes. 

Example: Abduction/adduction 

(b) Vertical axis: It passes vertically from inferior to superior and is formed by the intersection of the sagital and frontal planes. 

Example: Rotation type of movement 

(c) Frontal axis: It passes horizontally from left to right and is formed by the intersection of the frontal and transverse planes 

Example: Flexion and extension

Type of friction 

(a) Static friction 

(b) Dynamic 

(i) Sliding friction 

(ii) Roiling friction 

Friction: advantageous or disadvantageous with example. 

Friction is usually called a necessary evil. It means that it is essential in games and sports. Without friction we cannot give a better performance for example athletes use spikes and football players use studs to have appropriate friction, without friction they are unable to run fast. Even gymnasts use lime powder on their palms to perform on horizontal bar, Uneven bar and roman rings. On the other hand friction is disadvantageous in some games. In cycling there should not be more friction between road and the tyres of the cycle. If there is more friction there will be more wastage of energy of the rider and leads to damage of equipment.

Angular movement: To produce angular motion. movement has to occur around an axis. Human body has many joints and they all act as axis. The angular movements comprise of athletes, rotating, spinning. swinging, circling, turning, rolling, somersaulting and twisting. It may be athlete or any object that is turning through same angle. In many sports angular motion has great importance. e.g., a gymnast somersault in air, movement of hammer thrower and hammer is also angular, arm rotation at shoulder joint. 

Linear Movement: Linear motion is described by a straight line movement. It is also known as rectilinear translation. In this the athlete moves in the same direction. e.g., 100 m sprint. In general we can say that all human motions are combination of linear and angular motion, e.g.,a Gymnast balancing on a beam, a cycle racer etc. There is a rotational motion of pedals and wheels along with linear displacement of the cyclist.