CBSE Class 12 Physical Education –Chapter 8 Biomechanics and Sports- Study Materials

CBSE Class 12 Physical Education Important Questions Chapter 10 Biomechanics and Sports


1 Mark Questions

VERY SHORT ANSWER TYPE QUESTION
(1 MARK EACH)
Q1. Define trajectory?
Ans. The flight path followed by a projectile is called it’s trajectory.


Q2. What do you mean by sport biomechanics?
Ans. Sport biomechanics is the study of forces and stresses of human movements & their effects, atheletics performance and safety.


Q3. What is power?
Ans. The rate of doing work or using energy is called Power.


Q4. 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 force and the distance moved in the direction of the force.
Work Done = Constant force × Distance moved in the direction of the force


Q5. Explain Gravity?
Ans. Gravity is the force of attraction exerted by the earth towards it’s centre on a body or an object.


Q6. What is Air-resistance?
Ans. When a projectile moves through the air, it is slow down by air-resistance.


Q7. Define velocity?
Ans. The distance covered by an object per unit time is called velocity.



3 Mark Questions

SHORT ANSWER TYPE QUESTION (80 TO 90 WORDS) –
(3 MARKS EACH)
Q1. What is Energy? Explain about Kinetic & Potential Energy?
Ans. The Energy is the capacity to do work. There are various forms of energy.
Kinetic Energy:- It is defined as energy posessed by a body as a result of motion. It is called as—Kinetic energy =  mass × velocity
Potential Energy:- It is energy which is stored up in a body because of its position.
Potential Energy = mass × gravitational force × height of the body from ground (mgh)


Q2. Differentiate between Linear and Angular Motion?
Ans. Motions(Momentum) means a Change of position of a body and consists of the upsetting the equilibrium of a body.

LINEAR MOTIONANGULAR MOTION
When a body moves in a straight line, one point to other in the same linear motionWhen a body rotates it turns    about  from an axis, this rotation of the body is direction, is called angular motion.
Linear motion is measure in feet, Meters, KM etc.It is measure in degrees. 
Linear motion is of two types:Angular motion is of two types:-
Curvy linear motion- It is used When body travel on a curve path. 

Rotary motion is the movement which occurs when the axis of the body fixed, to the move around that particular point when the force is applied to it.
Visible Axis- It is that type which can See for example- hands of a clock. 

Invisible- An imaginary axis is that which cannot be seen. The axis is the causing
centre of the gravity of the body.
Example- A ball rotated in the air.

Q3. What is Friction ? Discuss various types of Friction.
Ans. Friction is the force that combats relative motion between the two surfaces that come in contact. Friction always acts in the opposite direction of the applied force. Friction can be of following types:-
Static friction:-the opposite force that comes into play when one body tends to move over the surface of another, but the actual motion has not yet started.
Dynamic friction:-the opposing for that comes into play when one body is actually moving over the surface of another body. Dynamic friction may be of two types.
Rolling friction:-the opposing force that comes into play when body is actually rolling over the surface of another body. For example, hockey/ cricket ball is hit.

Sliding friction:- The opposing force that comes into play when one body is actually sliding over the surface of the other body. For example- Ice skating.


Q4. Difference between Running and walking?
Ans.- 

  Running  Walking
Running is a process, in which both feet are off the ground.-Walking is a process, in which least one part of body (foot) remains in contact with the ground. 
There is double swing phase and whereas swing phase is longer.-There is longer stance phase the swing phase is shorter.
-The linear and angular velocity lower limbs is faster.-The linear and angular velocity of lower of 
limbs is slower.
-Running require greater range of motion.-Walking requires lesser range of   motion.

Q5. Is friction advantageous or disadvantageous in the field of games and sports? Give your comments with examples.
Ans. Friction is usually called necessary evil. It means it is essential in the life and we cannot do any work without it.

Advantages of frictionDisadvantages of friction
a. Keeps the object at position: By objects can be placed at position and shaped.a. Wear and tear of object:- Due to friction the there is wear and tear of object. 
Lubrication is used to allow the parts to move easier, moreover, prevents wear and tear.
b. Helps to move:- Frictional forces extra energy thus energy is It helps and running, walking.  
With Friction of feet/shoes on the surface
helps to speed. Frictional force helps
to move the object in the speed.
For example:- Spikes are used by the athletes to run fast.
b. Wastage of Energy:- Excess of means friction, helps to move the object being wasted.
c. Hold and grip of an object:-with the help of friction the ridges of skin of our fingers and palm enable us to grab and hold objects. 
For example:- in badminton the players use grip tohold it.
c. Slower down the speed:- In the roller sketting, Rolling shoes and  smooth surface are used to minimize friction.
d. Produce heat:- The law of conservation 
of energy states that the amount of energy remains constant. Thus, the energy is lost due to friction in trying to move and object is really turned into energy.
d. Makes movement difficult:- Friction can makes the job more difficult when one has to move the object. Excess friction can make it 
difficult to slide a box across the heat floor, walk through deep snow.

5 Marks Questions

LONG ANSWER TYPE QUESTION (5 MARKS EACH)
Ql. What is Projectile? Explain the factors affecting projectile trajectory?
Ans. Projectile:- An object thrown into the space either horizontally or an acute angle under the action of gravity is called a projectile. There are forces which act on a projectile gravitational force and air resistance.
Air resistance of an object varies greatly and it depends on the object’s particular shape and the atmospheric conditions in which the object is released.
The factors affecting Projectile

Trajectory are mentioned below.
a. Angle of projection:- An object which is projected at different angles covers different distances. When it is projected or released at angle of 30, making it a parabolic path and covers lesser distance. When it is projected at 60, it covers a distance less that 30. When it is released at an angle of 45, makes a parabolic path and covers maximum distance. So the distance covered by an object (short-put, hammer, javeline, discus etc. depends on the angle of release of projectile)
b. Height of release:- The higher the level of release, the greater distance is covered in flight, this is because the higher projectile is released. The longer it will be in the air. The horizontal component will be acting on the projectile for longer.
c. Speed of release (initialvelocity):- The speed or velocity is directly related to the distance covered in flight. The speed of release depends on initial vertical

velocity and initial horizontal velocity. Having higher horizontal velocity will increase the length of flight time and therefore the distance covered. This would be an advantage in sports which primarily requires good distance in long jump, sky jump etc.
d. Gravity:- gravity acts on a body or object to give it mass. The greater the weight of an object, the greater the influence of gravity upon it. Gravity will effect a projectile as well as it will decrease the height, the projectile can obtain. For example:-a cricket ball can be thrown at greater distance in comparison to shotput.

e. Air Resistance:- When a projectile moves through the air, it is slow down by an air resistance. Air resistance decreases the horizontal component of a projectile. The effect of air resistance is very small but it need to be taken into consideration if you want to increase the horizontal components of a projectile. The factors are related to the amount of air resistance acting on a projectile-mass, surface of the object, surface of the volume ratio. Trajectory Initial Horizontal Velocity Vertical Component Initial Vertical Velocity Horizontal Component
f. Spin:- The amount and direction of spin acting on a projectile will directly effect the distance while travel.
The main reason behind this fact is the air pressure acting on the object.


Q2. Discuss the mechanical analysis of walking in details?
Ans. Mechanical analysis of walking can be studied in two fields
Stance phaser:- 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 the part of stance phase, both the feet have a contact with the ground for a period of time. The stance phase of walking is divided into five stages.
·Heel Strike – This stage begins when the feet first touches the ground and continuous until the complete foot is on the ground i.e. early flat foot stage.
·Early Flat Foot – The starting of this stage is that movement when the complete foot is on the ground and early flat foot stage occurs when the body’s centre of gravity passes over the top of the foot. The centre of gravity of the body is located approx. In the palvic area of the lower spine while walking. The main purpose of this stage is to allow the foot to act as a shock absorber.
·Late Flat Foot – An athlete comes into late flat foot stage when his body’s centre of gravity passes in front of ‘ neutral position. This stage lasts when the heel lifts off the ground. During this stage the foot needs to go from being a shock absorber to being a rigid lever which can help to prople the body in forward direction.
·Heel Rise – This stage starts when the heel begins to leave the ground. The foot functions are a rigid lever to move the body in forward direction. During this stage of walking, the ground forces that go through the foot are very efficient. -Toe off-this stage begins when the toes leave the ground completely. This stage continues until the beginning of swing phase.
Swing Phase:-It occurs when one foot is on the ground and other one is in the air. Swing phase in walking is shorter than The stance phase. It is divided into three phases
Initial swings:- This phase sees the hip extended to 10o and then going onto flexion and knee flexed to 40-60o and the Ankle changing it’s position from the flexion to neutral.
Mid swing:- This phase sees the hip extended to 30o, the knee flexion till 60o and extended approx to 30o and ankle become dorsiflexed.
Terminal Swing:-This phase is the hip flexed till 30o and the knee is locked extension and foot changes its position from Dorsiflexed to neutral.


Q3. What are the different phases of running cycle?
Ans. Running is an essential part of living beings. Running is important in sports also. A good runner will not only be able to defeat it’s opponents in running, but would also be able to gain very good takeoff velocity that would help to take a higher or longer jump.
Different phases of running are mentioned below.

Running style/ 
Phases
SprintingFast RunningJogging
Initial ContactThis phase sees the front 
Of the foot of the sprinter
making contact with the
ground. Their heel might
or might not touch the
ground later depending
on their personal running
Technique.
This phase sees the 
Middle of the foot or
Heel of the fast Runner make contact with the ground.
This phase the full foot or the heel of the jogger make contact with the 
ground.
Mid-StanceThis phase is very quick 
and the sprinter’s foot is
usually in the same
position as in the phase
of the initial contact.
This phase is very 
Quick and the fast
Runner will spend
This phase in mid-
Stance as he pushes
through with this
foot.
In comparison to sprinters and the fast runners who use their feet and ankle to move into the next phase, 
Joggers tend to move their Centre of gravity forward to do the same.
ProplusionThis phase see the hips of 
The sprinter extending
Back ready to propel him
Forward to take-off. His
Arms simultaneously swing at full power to help him.
The fast runner 
Receives propulsion
Through the big toe
With  his hips extended back and knee Slightly bent.
The jogger will receive Propulsion through the big toe. But if the hips of  the jogger are not fully extended back, then the 
Propulsion is received from the other toes. The
Arms of the jogger only move a small amount.
SwingThe non-supporting leg of 
The sprinter swings high
With the knee at almost
At an angle of 90.
The knee of the 
Supporting leg of
The fast runner will
Be lifted, although
Not not as high as
That of a sprinter.
The knee of your non-supporting leg of the jogger remains low and 
only slightly bent.

 

Physical Education Class 12 Important Questions Chapter 8  Biomechanics and Sports

1 Mark Questions

Question 1.
What is the difference between axis and plane?
Answer:
An axis is an imaginary line about which the body or limb rotates. A plane is an imaginary flat surface along which a movement takes place.

Question 2.
Elucidate projectile motion.
Answer:
It refers to the motion of an object projected into the air at an angle.

Question 3.
An object thrown into space either horizontally or at an acute angle under the action of gravity is called a projectile. Name the two forces which act on a projectile. All India 2017
Answer:
The two forces that act on a projectile are. propelling force and force of gravity.

Question 4.
What is the first law of Newton?
Answer:
This law states that a body at rest will remain at rest and a body in motion will remain ill motion at the same speed and in the same direction till any external force is applied on it to change state.

Question 5.
Explain what is ‘dynamic friction’? (All India 2016)
Answer:
Dynamic friction is the opposing force that comes into play when one body is actually moving over the surface of another body. Dynamic friction may be of two types i.e. sliding friction and rolling friction.

Question 6.
Enlist the methods of reducing friction.
Answer:
Methods of reducing friction are

  • Polishing
  • Lubrication
  • Use of ball bearings
  • Streamlining

3 Marks Questions

Question 7.
What is axis? What are its types?
Answer:
An axis is an imaginary line about which the body (or limb) rotates. It can he divided in three parts

  1. Frontal Horizontal Axis Axis of the body that passes horizontally from side to side at. right angles to the sagittal plane.
  2. Vertical Axis Axis of the body that passes from head to foot.at right angles to the transverse plane.
  3. Sagittal Horizontal Axis Axis of the body. that passes from front to rear lying at right angles to the frontal plane.

Question 8.
What do you mean by plane? Explain its types
Answer:
A plane is an imaginary flat surface along which a movement takes place. It can be divided into three parts as follows :

  • Sagittal Plane A vertical plane of the body. which passes from front to rear dividing the body into two symmetrical halves.
  • Transverse Plane Any horizontal plane of the body which is parallel to the diaphragm; also called the horizontal plane.
  • Frontal Plane Plane of the body which passes from side to side at right angles to the sagittal plane; also called the coronal plane.

Question 9.
Enumerate the laws of motion:
Answer:
The three laws of motion are

  1. Newtons 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.
  2. Newtons Second Law of Motion This law states that the acceleration of an object is directly proportional to the force producing it and inversely proportional to its mass.
    a=Fm where aF,a1m
  3. Newtons 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.

Question 10.
How Newton’s second law and third law of motion can be applied in sports.
Answer:
Second Laws 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 counter force 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 another unstable surface.

Question 11.
“Friction is a necessary evil.” Justify your answer with suitable examples from sport. (CBSE Model Question Paper 2015)
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.

5 Marks Questions

Question 12.
Describe different types of movements.
Answer:
Physical activity is made possible by movements and motions. Every movement takes place in one plane and around one axis.
They are categorised by movement type as follows

  1. Flexion It takes place when the angle decreases between the two bones attached to a joint.
  2. Extension It takes place when the angle between the two bones attached to a joint increase. Both flexion and extension occur in the sagittal plane about the frontal axis.
  3. Adduction It is a movement laterally toward the middle of the body.
  4. Abduction It is a movement laterally away from the middle of the body. Both adduction and abduction occur in the frontal plane about the sagittal axis.

Question 13.
What are the major muscles that we use while we run?
Answer:
Following are the four muscles that we use while we run
(i) Quads (Quadriceps Femoris) Quads are muscle groups of four basic muscles located on our front thighs. They are

  • The rectus femoris
  • The vastus medialis
  • The vastus lateralis
  • The vastus intermedius.

Our quads are responsible for moving two of the joints used in running our knee joint and our hip joint. They work together to straighten our knees and bend our hips.
(ii) Quads (Quadriceps Femoris) Our hamstrings are made up of four muscle-parts on the back of your thighs. These are known as

  • The semitendinosus
  • The semimembranosus
  • The biceps femoris
    (two parts long head and short head).

These four parts of our hamstrings allow us to flex our knees. The semitendinosus semimembranosus and the long head biceps femoris work together to extend the hips.
(iii) Hip Flexors (Iliopsoas) Our hip flexors (or iliopsoas) like our quads is comprised of a muscle group of two muscles

  • The iliacus
  • The psoas major

To our right the shortest muscle the iliacus begins on our pelvic crest (the iliac fossa) and stretches over to our thigh bone (femur). The larger of the muscles the psoas major stretches from our T-12 spinal vertebrae to our L-5 spinal vertebrae and there attaches to the femur. These two muscles work together to help our hips flex.

(iv) Calf Muscles Our calf muscles are located on the back of our leg below our knee. Though many anatomists see the calf muscle to be a single muscle (triceps surae) most say that it is a muscle group like our quads and hip flexors. This group consists of two main muscles

  • The gastrocnemius
  • The soleus

Our calf muscles will allow us to flex our knee and planter flex our ankle. Like our quads our calf muscles can be strengthened by doing squats. Other good strength-building exercises would include calf muscle raises and skipping!

Question 14.
Which muscles are used in jumping?
Answer:
Following muscles are used in jumping
1. Quadriceps The quadriceps rest on the front of thethighs and they have four components: the vastus medial vastus lateral rectus femoris and vastus intermedius. During a jump you perform hip flexion and knee extension which both activate the quadriceps. Hip flexion takes place when you move your thigh toward your stomach; knee extension takes place when you straighten your leg. A squat is a specific exercise that can help you gain more strength in the quads.

2. Hamstrings The hamstrings are opposing muscles to the quadriceps and have an opposite function. You activate your hamstrings through hip extension and knee flexion. Hip extension takes place when you bend your knee and move your heel toward your butt. Hip extension also causes you to work the glutes. From an anatomical standpoint the hamstrings have three parts: the biceps femoris semimembranosus. All parts get activated during the lowering phase and the explosive phase of a jump. A squat works the hamstrings but you can place more emphasis on them by doing a lunge.

3. Hip Flexors The hip flexors run from the lower stomach to the top of the thighs. They consist of the psoas major and iliacus and because of this they are often referred to as the iliopsoas. As the name implies these muscles get activated when you flex your hip in similar fashion to the quads.
Although these muscles are small they are important for explosive motions like sprinting a jumping. A lying leg raise is a good exercise to strengthen the hip flexors.

4. Calves The calyes hav.e two parts the gastrocnemius and soleus. The gastrocnemius has a lateral head and medial head and it is easily seen on the back of the leg right below the knee. The soleus sits anterior or in front of the gastrocnemius-. Both parts function to plantar-flex the foot. This motion occurs when you jump off the ground and point your toes downward.
Jumping rope is a good cardiovascular exercise to train these muscles because of the repetitive hopping you do on your toes. A tuck jump is a good exercise to.work your calves because it is specific to jumping.

Question 15.
Which muscles do we use in throwing?
Answer:
Following are the muscles which are used While throwing anything like ball football etc

  1. Shoulder Muscles The deltoids are the muscles of your shoulder which play a crucial role in rotating your arm. Always warm up adequately by performing arm circles to avoid injuring your rotator cuff while performing shoulder exercises.
  2. Triceps Your triceps are located on the back of your upper arm and aid in the process of extending your arm at the elbow. This action helps you release the ball with force and pushlt in the desired direction. To strengthen your triceps efficiently perform exercises such as triceps pushdowns with a rope or pulley and close-grip bench presses.
  3. Latissimus Dorsi Your latissimus dorsi often referred to as your lats are located on either side of your spine. These large muscles help produce force for throwing and help transfer epergy from your legs to your upper body. Among the best exercises for strengthening your lats are pull upsseated cable rows and bent-over barbell rows.
  4. Abdominals While many people exercise their abdominal muscles in hopes of attaining a six-pack this muscle group is highly functional as well. A strong core facilitates the transfer of power from your lower body to your upper body enabling your throws to benefit from the strength of your legs. Among the best exercises for your abs are hanging leg raises and Swiss ball crunch.
  5. Quadriceps The quadriceps is the major muscle group located on the front of your thigh. This large group of muscle tissue helps you power the ball toward your intended target as you step into your throw. Among the most effective exercises for the quadriceps are the barbell step-up barbell lunge and barbell squats which also work your abdominal muscles.

Question 16.
Define trajectory. Describe the factors affecting the trajectory of a projectile. Delhi 2016
Answer:
A trajectory is a path described by a moving object or the path followed by a projectile. Examples are kicking a soccer ball a throw in cricket throwing a hammer etc.
Factors affecting projectile trajectory are
1. Propelling Force The propelling force produces certain effects depending upon its point and direction of application. If the application is directly through the projectiles 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 objects 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.

2. 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

  • weight (mass) of the object
  • amount of force driving it upward
  • the effects of air resistance on the object.

3. 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 17.
Elucidate the types of friction.
Answer:
The force acting along two surfaces in cozntact 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.
Two types of friction are

  1. Static Friction The opposing force that comes into play when one body tends to move over another surface but the actual motion has not yet started.
  2. 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. Dynamic friction may be of two types i.e. sliding friction and rolling friction.

Question 18.
What is friction? Is it advantageous and disadvantageous in the field of games and sports? All Indio 2017
Answer:
Friction is the force acting along two surfaces in contact which opposes the motion of one body over the other. It has very importance in sports. For example when a cricket ball or hockey ball is hit it moves very fast in the direction of force in the ground. After sometimes its motion becomes less and ultimately it comes in static position.

Advantages
Friction has a great significance in the field of sports. Many sports require more friction and other need lesser friction. In some sports we can not give a better performance without friction. For example in athletics the shoes are designed to increase friction so that better speed can be generated.

The spikes have small nails to crease the friction. Gymnasts sometimes use lime on their palms to perform on horizontal bar uneven bars to increase friction. In these sports friction is necessary thus regarded as advantageous.

Disadvantages
On the other hand some games do not require friction. For example the games like snow skiing the skiis are designed to have minimum friction. In cycling there should not be more friction between road and tyres of the cycle. Thus the tyre should be fully inflated to reduce the force of friction. If there is more friction it will be more wastage of energy of the cyclist. Moreover the cyclists use pointed helmets silk body fitted costume and bend their bodies while cycling to reduce air friction.

Swimmers use goggles cap and full body swimsuit to reduce the force of friction caused by water. In roller skating less friction is also needed for better performance. Thus in these games friction is regarded as disadvantageous.

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

  1. Polishing surfaces in contact
  2. Lubrication
  3. Use of ball bearings
  4.  Streamlining
  5. Changing the type of material used

3 Marks Questions
Question.6. Write the formula for calculating work, energy and power?
Answer.
Physical Education Class 12 Important Questions Chapter 10 Kinesiology Biomechanics and Sports 1

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.
Physical Education Class 12 Important Questions Chapter 10 Kinesiology Biomechanics and Sports 2

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

  1.  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.
  2.  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.
    Physical Education Class 12 Important Questions Chapter 10 Kinesiology Biomechanics and Sports 3
  3.  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

  1.  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.
  2.  The Force Arm It is the point at which the force is applied.
  3.  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

  1.  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.
  2.  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.
  3. 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

  1. 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.
  2.  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.
  3. 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.
  4.  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.
  5.  Toe Off This stage begins when the toes leave the ground completely. This stage continues until the beginning of the swing phase.
  6.  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:

  1.  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.
  2.  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.
  3.  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.
Physical Education Class 12 Important Questions Chapter 10 Kinesiology Biomechanics and Sports 4
Straight line is defined as the shortest distance between two points.
It can take place in two ways :

  1.  Going Straight (Rectilinear) Covering a straight distance.
  2. 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.
    Physical Education Class 12 Important Questions Chapter 10 Kinesiology Biomechanics and Sports 5
    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:

  1.  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.
  2.  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.
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