# CBSE Class 12 Phy. Edu. Unit-10-Biomechanics and Sports

Unit 10 - Biomechanics and Sports

Introduction

Today, biomechanics is playing a very important role in improving the performance of sportspersons. Now-a-days, physical education teachers, coaches and physical trainers are concerned with helping individuals to learn how to move efficiently and effectively. The teachers as well as coaches always make their best efforts to improve the performance of students in various competitive games and sports. They can improve the performance of students if they have sufficient knowledge of Biomechanics.

Definitions of Biomechanics

Sports can be described as the physics of sports. In this subfield of biomechanics, the laws of mechanics are applied in order to gain a greater understanding of athletic performance through mathematical modelling, computer simulation and measurement.

1. According to Webster Encyclopedia—“Biomechanics is the study of the action of external and internal forces on the living body.”

2. According to Wikipedia—“Biomechanics is the study of the structure and function of biological system of humans.”

Very Short Answer Type Questions (1 Mark)

Q1. Elaborate the term Biomechanics.

Ans. Biomechanics is the science that examines the internal and external forces acting on a human body and the effects produced by these forces.

Q2. Elucidate projectile motion.

Ans. When a body is thrown at a certain angle with a certain amount of force into the air, it travels in the air and covers some distance following a curved path called a parabola. This is called projectile motion.

Q3. Define linear motion.

Ans. Linear motion occurs when all the parts of a body move the same distance in the same direction in the same time. The term linear refers to a straight line.

Q4. Give one most important mechanical difference between walking and running.

Ans. The body is totally airborne for a period of time during running, whereas at least one foot contacts the ground for the whole cycle during walking.

Q5. What is a projectile?

Ans. An object thrown into the space either horizontally or an acute angle under the action of gravity is called a projectile. There are two forces which act on a projectile:

(a) Gravitational force

(b) Air resistance.

Q6. What is gravity?

Ans. It is the force of attraction exerted by the earth towards its centre on a body or an object. The greater the weight of an object, the greater the influence of gravity upon it. Gravity affects a projectile as it decreases the height a projectile can obtain.

Q7. What do you mean by air resistance?

Ans. When a projectile moves through the air, it is slowed down by air resistance. Air resistance decreases the horizontal component of a projectile. The effect of air resistance is very small, but it needs to be taken into consideration if you want to increase the horizontal component of a projectile.

Q8. What is angular motion?

Ans. Angular motion is also referred to as rotatory motion. It occurs when all points on a body or object move in circular or circular parts of circle about the same fix central line or axis. Angular motion can occur about an axis with the body or outside the body.

Q9. Define work.

Ans. Work refers to an activity involving a force and the movement in the direction of the force. It can also be defined as the work done by a constant force as the product of the force and the distance moved in the direction of the force.

Work = Force x Distance

Q10. Define power.

Ans. Power is the rate of doing work or the rate of using energy. The above definition can be expressed as an equation.

Power = Work/Time

Q11. Define Energy.

Ans. Energy is the capacity to do work. However, there are various forms of energy but in the field of games and sports our main concern is about mechanical energy. Mechanical energy is the combination of kinetic and potential energy.

Q12. State Static Friction.

Ans. The opposing force that comes into play when one body tends to move over the surface of another but the actual motion has not yet started, is called static friction.

Short Answer Type Questions (3 Marks)

Q1. State any two factors which affect the projectile trajectory.

Ans. 1. Any object when projected at different angles covers different distances. When it is projected or released at the angle of 30° making a parabolic path, it covers less distance i.e., AB. When it is projected at the angle of 60°, it covers, a distance i.e., AC and when it is release at the angle of 45° making a parabolic path it covers the maximum distance i.e., AD. Here it is supposed that the initial velocity in all the cases is same.

2. The distance covered by an object depends on the initial velocity of the projectile. If the initial velocity is more, the object covers maximum distance. On the other hand, if initial velocity is less, the object covers less distance.

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Q2. Elucidate kinetic energy and potential energy.

Ans. Kinetic Energy: The energy an object has because of its motion is called kinetic energy. The kinetic energy of a moving object depends on its speed. The faster the object moves, the greater the kinetic energy it has. For example, if a javelin travels with maximum speed then it has more kinetic energy. When it slows down it loses its kinetic energy and when it touches the ground, it has no kinetic energy.

Potential Energy: Potential energy is the energy stored in an object because of its position or condition. For example, when you stretch a bow, it acquires the ability of releasing an arrow with speed. It means that the stretched bow also has potential energy.

Q3. What is the difference between kinetic and potential energy?

Ans. 1. Kinetic Energy: Moving object has the capacity to do work due to its motion. Mass and velocity of an object affects kinetic energy and the capacity to do work. Kinetic energy is proportional to the square of the velocity.

2. Potential Energy: It is energy of an object due to positive gravitational energy due to an object’s position relative to the earth. Strain energy due to the deformation of an object. Gravitational potential energy is related to the object’s weight and its elevation or height above the ground or some reference point. Strain energy— Energy due to the deformation of an object related to stiffness, material properties and its formation.

Q4. Discuss various types of friction.

Ans. 1. Static Friction: The opposing force that comes into play when one body tends to more over the surface of another, but the actual motion has not yet started, is called static friction.

2. Dynamic Friction: Dynamic friction is the opposing force that comes into play when one body is actually moving over the surface of another body. Further, dynamic friction may be of two types i.e., sliding friction and rolling friction.

Q5. What are the factors which affect projectile trajectory?

Ans. 1. Angle of projection: Any object when projected at different angles covers different distance. When it is projected or released at the angle of 30° making a parabolic path, it covers less distance. When it is projected at the angle of 60°, it covers a distance less than the distance covered by 30° angle. When it is released at the angle of 45° making a parabolic path it covers the maximum distance. Here it is supposed that the initial velocity in all the case is same.

2. Initial Velocity: The distance covered by an object depends on the initial velocity of the projectile. If the initial velocity is more the object covers maximum distance. On the other hand, if initial velocity is less, the object covers less distance.

3. Gravity: It is the force of attraction exerted by the earth towards its centre on a body or an object. The greater the weight of an object the greater the influence of gravity upon it. Gravity affects a projectile as it decreases the height of projectile can obtain.

Q6. What is projectile? State any one factor which affect projectile trajectory.

Ans. An object thrown into the space either horizontally or an acute angle under the action of gravity is called a projectile. There are two forces which act on a projectile—gravitational force and air resistance.

Spin also affects the flight of an object. In fact, the amount and direction of spin acting on a projectile directly affects the distance covered or travelled by a projectile. The main reason behind this fact is the air pressure acting on the ball. For example: in a tennis shot top spin gives a poorer distance in comparison to back spin. As a matter of fact, a top spin shot creates a region of high pressure on the top of the ball and low pressure under the ball. Air moves from high to low pressure and as a result the ball dips suddenly and less distance is covered or travelled.

Q7. Is friction advantageous or disadvantageous in the field of sports of games and sports?

Ans. Advantage: 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 in the field of sports. For example, athletes (racers and jumpers) use spikes and football players use studs to have appropriate friction while they run fast. Without friction they are unable to run fast. Even gymnasts use lime on their palms to perform on horizontal bar, uneven bars and roman rings to have friction.

Disadvantage: On the other hand, friction is disadvantageous in some of the sports and games, such as in cycling, there should not be more friction between road and the tyres of cycle. If there is more friction there will be more wastage of energy of the rider. The tyres must be fully inflated to reduce the force of friction in cycling. In roller skating, there should be less friction for better performance.

Consequently it can he said it is advantageous in some of the sports and disadvantageous in others.

Long Answer Type Questions (5 Marks)

Q1. Discuss the angular and linear movement in detail.

Ans. The movement of an object can be classified in three different ways. Movement can be linear, angular or a mix of linear and angular which is simply called a general motion.

Linear motion: Linear motion refers to any motion that moves along a straight line in one direction. The direction can either be in a horizontal, vertical or inclined direction. As a matter of fact, linear motion describes a situation in which movement occurs in a straight line. It occurs when all points of body object or the athlete moves the same distance in the same direction and at the same time frame.

Angular motion: Angular motion is also referred as rotatory motion. It occurs when all points on a body or object move in circular or circular parts of circle about the same fixed central line or axis. Angular motion can occur about an axis with the body or outside the body. A child swing is an example of angular motion about an axis of rotation external to the body. An ice skater in a spin is an example of angular motion about an axis or within the body.

Q2. Discuss the mechanical analysis of walking in detail.

Ans. Mechanical analysis of walking can be studied in two phases:

1. Stance phase.

2. Swing phase.

1. Stance phase: Stance phase is the time when the foot is on the ground. It is considered that it consists of maximum percentage of walking cycle. For a part of the stance phase both feet have a contact with the ground for a period of time. The stance phase of walking can further be divided into the following stages.

(i) Heel strike: This stage begins when the heel first touches the ground and continues until the complete foot is on the ground i.e. early flat-foot stage.

(ii) Early flat-foot: The standing of the early flat-foot stage is that moment when the complete foot is on the ground. The end early flat-foot stage occurs when the body’s centre of gravity (COG) passes over the top of the foot.

(iii) Late flat-foot: An athlete comes into late flat-foot stage when his body’s C04 passes in front of the neutral position. This stage lasts when the heel lifts off the ground.

(iv) Heel rise: This stage starts when the heel begins to leave the ground. The foot functions as a rigid liner to move the body in forward direction.

(v) Toe off: This stage begins when the toes leave the ground completely. This stage continues until the beginning of swing phase.

2. Swing phase: Swing phase occurs when one foot is on the ground and the other one in the air. The foot which is in the air is called to be in the swing phase. The swing phase in walking is shorter than stance phase.

Q3. Describe the factors affecting the trajectory of a projectile.

Ans. Factors affecting projectile trajectory are:

(ì) Propelling Force: The propelling force produces certain effects depending upon its point and direction of application. If the application is directly through the projectile's centre of gravity, only linear motion results from the force. As the projecting force is moved further from the centre of gravity, rotator motion of the object increases at the expense of linear motion. If the force is below the object's centre of gravity, backspin is results. Forward spin results when the force is above the centre of gravity. When the force is off centre to the left, clockwise spin results and when it is off centre to right, counter clockwise spin occurs.

(ii) Force of Gravity: As soon as contact is broken with a projected object, the force of gravity begins to diminish the upward velocity of the object. Finally, gravity overcomes the effects of the upward component of the projectile's motion and the object begins to descend. The factors that determine how soon gravity will cause the object to descend are:

(a) Weight (mass) of the object

(b) Amount of force driving it upward

(c) The effect of air resistance on the object.

(iii) Effect of Air Resistance: As the speed of an object increases, air resistance has a greater retarding effect. The more surface area an object presents in the direction of movement, the greater will be the effect of air resistance.

Q4. Elucidate the types of friction.

Ans. The force acting along two surfaces in contact which oppose\ the motion of one body over the other is called the force of friction. It is very important in sports. That · lagged the area of contact between the surfaces, the greater is the force of friction. When both the surfaces are smooth, the force of friction reduces to almost zero. Three types of friction are:

(i) Static Friction:  The opposing force that comes into plc when one body tends to move over the surface but the actual motion has not yet red.

(ii) Limiting Friction: Limiting friction is the maximum of thing force that comes into play when one body is just on the verge of moving over the surface of another body.

(iii) Kinetic Friction: Kinetic friction is the opposing force at comes into play when one body is actually moving over the surface of another body.

Q5. Discuss the mechanical analysis of running.

Ans. Running is an important skill in almost every sports event. The mechanics of running are similar in several respects to those of walking. The most notable factors differentiating a run from a walk is the period of double support, which is not present in running. Running has the following phases:

(a) Swing Phase: The swing phase begins with the toe off the ground and ends with the foot landing. Since the body moves faster in running, the leg should move forward with more speed. It is flexed considerably more as compared to walking. The leg's weight is brought closer to the hip, since the lever is shortened by flexion of the knee, reducing the moment of inertia and increasing the angular velocity.

(b) Support Phase:  The foot strikes the ground under the knee and under the centre of gravity. The leg strikes the ground with the bail of the foot. During the propulsive action, the vertical components should be kept as small as possible, being just enough to counteract gravity's downward pull so that a great proportion of the force can be used effectively in driving the body forward, rather than be wasted in producing a bouncing run. Arms swing must be co-ordinated with the legs to keep the balance of the rotatory effect of the Leg 'swing on the trunk. Since the legs are moving faster, the arms must move faster.

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