CBSE Class 12 Physical Education Chapter 10 Biomechanics and Sports
Physical EducationNCERT SolutionsRD Sharma Solutions
1 Mark Questions
Question.1. Elaborate the term Biomechanics.
Answer. Biomechanics is the science that examines the internal and external forces acting on a human body and the effects produced by these forces.
Question.2. Elucidate projectile motion.
Answer. 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.
Question.3. Define linear motion.
Answer. 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.
Question.4. Give one most important mechanical difference between walking and running.
Answer. 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.
Question.5. Enlist the methods of reducing friction.
Answer. Methods of reducing friction are
- Polishing surfaces in contact
- Use of ball bearings
- Changing the type of material used
3 Marks Questions
Question.6. Write the formula for calculating work, energy and power?
Question.7. What do you mean by work? If a person applies a force of 10 pounds to an object and displaces it 21 feet, calculate the work done.
Answer. Work is defined as the product of force and the distance through which the object moves in the direction of application of the force.
Applied force = 10 pounds
Displacement = 21 feet Work = Force x Displacement Work = 10 x 21 = 210 ft -lb
Question.8. What is power? What will be the units of power expressed using foot, pound and second? If a weightlifter does 1500 ft-lb of work in raising a barbell overhead and does it for 5 seconds, calculate the power applied by the athlete.
Answer. Power is the rate of doing work or the rate of energy expenditure.
Question.9. Briefly explain at which angle we throw an object to cover the maximum distance.
Answer. Projectile motion refers to the motion of an object projected into the air at an angle. A few examples of this include a soccer ball being kicked, a baseball being thrown or an athlete long jumping.
For covering maximum horizontal distance the thrower must ideally throw the implement at 45 ° at maximum velocity. However, this angle is generally less than 45 ° actually depending on the weight of the implement.
Question.10. Enumerate the laws of motion.
Answer. The three Laws of Motion are
- 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.
- Newton’s Second Law of Motion This law states that the acceleration of an object is directly proportional tathe force producing it and inversely proportional to its mass.
- Newton’s Third Law of Motion This law states that to every action, there is always an equal and opposite reaction.
Question.11. Explain why the angles of release for shot put, javelin and discus throw are different?
Answer. To achieve maximum distance for any of these events, the athlete will have to balance three components – speed, technique and strength. As the angle of release increases, the athlete must expend more energy in overcoming the weight of the object thrown and so less effort is available to develop the release speed of the object. Further, the structure of the body favours a throw in the horizontal direction. As the three objects are differing in weight, the athlete expends different amounts of energy in overcoming their weight. Accordingly, the athlete will release the javelin at a smaller angle of release than the shot put, as the javelin is lighter. The same reason holds for the discus.
Question.12. “Friction is a necessary evil “. Justify your answer with suitable examples from sport.
Answer. 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. Examples are spikes used by athletes for running and studs used in football boots of the players. However, friction has disadvantages also. In cycling, there should not be more friction between road and the tyres of the cycle.
Question.13. Explain the functioning of Levers.
Answer. The functioning of a lever is characterised by three main parts. These are
- The Fulcrum It is the point at which the lever rotates or turns and which identifies the lever class by its position in relation to the other two parts. In human movement, the fulcrum is the joint which dictates the kind of action.
- The Force Arm It is the point at which the force is applied.
- The Load / Resistance Arm It is the point where the load or resistance is located.
5 Marks Questions
Question.14. Describe the factors affecting the trajectory of a projectile.
Answer. Factors affecting projectile trajectory are
- 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, rotatory motion of the object increases at the expense of linear motion. If the force is below the object’s centre of gravity, backspin 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.
- 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.
- 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.
Question.15. Mechanically analyse an athlete walking on the road.
Answer. Walking can be studied in two phases, called as stance phase and swing phase. It proceeds as given below
- Heel Strike This stage starts the stance phase. It begins when the heel first touches the ground and continues until the complete foot is on the ground.
- Early Flat Foot It starts from the moment when the complete foot is on the ground. It occurs when the body’s centre of gravity passes over the top of the toe. The main purpose is to allow the foot to act as a shock absorber.
- Late Flat Foot This stage starts when the body’s Centre of Gravity passes in front of the neutral position. This stage lasts till when the heel lifts off the ground.
- Heel Rise This stage starts when the heel begins to leave the ground. In this stage, the ground forces that go through the foot are very significant.
- Toe Off This stage begins when the toes leave the ground completely. This stage continues until the beginning of the swing phase.
- Swing Phase This stage starts when one foot is on the ground and the other one in the air. This is shorter than the stance phase.
Question.16. Elucidate the types of friction.
Answer. The force acting along two surfaces in contact which opposes the motion of one body over the other is called the force of friction. It is very important in sports. The larger 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:
- Static Friction The opposing force that comes into play when one body tends to move over the another surface but the actual motion has not yet started.
- Limiting Friction Limiting friction is the maximum opposing force that comes into play when one body is just on the verge of moving over the surface of another body.
- Kinetic Friction Kinetic friction is the opposing force that comes into play when one body is actually moving over the surface of another body.
Question.17. Describe linear and angular motion with their characteristics.
Answer. Linear Motion This 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 straight line motion of a body from one point to another point.
Straight line is defined as the shortest distance between two points.
It can take place in two ways :
- Going Straight (Rectilinear) Covering a straight distance.
- Going in a Curved Path (Curvilinear) It is possible for a body to move along a curved path and still satisfy the conditions of linear motion.
Angular Motion Also known as rotation, rotatory motion or circular motion. This occurs when a body moves on a circular path about a central line so that all parts of the body move through the same angle in the same direction in the same time.
The central line which lies at right angles to the plane of motion is known as the axis of rotation. It may be physical or imaginary. It also may be inside or outside the body.
Question.18. Discuss the mechanical analysis of Running.
Answer. 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:
- 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.
- Support Phase The foot strikes the ground under the knee and under the centre of gravity. The leg strikes the ground with the ball 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 pulj-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.