Physical Education Class 12 Chapter 8 Notes - Biomechanics & Sports | CBSE

Unit VIII - Biomechanics & Sports

● Newton’s Law of Motion & its application in sports 
● Equilibrium – Dynamic & Static and Centre of Gravity and its application in sports 
● Friction & Sports 
● Projectile in Sports

Physical Education Class 12 Chapter 8 Notes - Biomechanics & Sports | CBSE

Biomechanics is the study of forces and their effects on living systems.

Newton's laws of motion

Three Laws

1. Law of Inertia

  • This is the first law of newton
  • According to this law, " A body at rest will remain at rest and body in motion will keep moving at same speed and direction until and unless an external force is applied"
  • In sports, this law is applied in various ways, such as in kicking a ball. Once the ball is kicked, it will continue to move in a straight line with the same velocity until an external force, such as friction or air resistance, acts on it.

2. Law of Acceleration

  • This is the Newton’s Second Law.
  • A change in acceleration is directly proportional to force production and inversely proportional to its mass
  • F=ma
  • This law is applied in various sports, such as in weightlifting. The more force a weightlifter can apply to the barbell, the greater the acceleration and the greater the chance of lifting the weight.

3. Law of Reaction

  • This is the Newton’s Third Law.
  • Every action has an equal and opposite action.
  • Application of this law-
    • Shooting- The pistol is fired, the bullet moves forward (action), pistol jerks backwards (reaction).
    • Swimming- The swimmer pushes the water backward (action), and the water pushes the swimmer forward (reaction).
    • Similarly- High Jump, Walking, etc.


Equilibrium refers to a state of balance or stability in a system. In physics, equilibrium can be classified into two types: static and dynamic.

Static equilibrium is when an object is at rest and has no movement. It occurs when the sum of all the forces acting on an object is zero, and the object remains stationary. For example, a book placed on a table is in static equilibrium as the forces acting on it, such as gravity and the normal force of the table, are balanced.

Dynamic equilibrium is when an object is in motion but has a constant velocity. It occurs when the sum of all the forces acting on an object is zero and the object continues to move at a constant speed in a straight line. For example, a car travelling on a straight, level road at a constant speed is in dynamic equilibrium as the forces acting on it, such as the engine and air resistance, are balanced.

In summary, static equilibrium refers to a stationary object with balanced forces, while dynamic equilibrium refers to a moving object with balanced forces.

Centre of Gravity

The centre of gravity (COG) refers to the point in an object where the weight is evenly balanced in all directions. In humans, it is the point around which the body's mass is equally distributed. In sports, understanding the concept of the COG is crucial for maintaining balance and control while performing different movements.

Its application in sports 

The application of COG in sports is varied and includes:

Balance: In sports such as gymnastics, diving, and figure skating, balance is essential for success. Understanding the position of the COG and controlling it helps athletes maintain their balance while performing complex movements.

Stability: The position of the COG also determines an athlete's stability. Lowering the COG, for example, by bending the knees in a squat, makes the athlete more stable and helps them maintain balance.

Momentum: In sports such as throwing, understanding the COG helps athletes generate momentum. The transfer of weight from the back leg to the front leg in a baseball pitch, for example, requires a shift in the COG to generate momentum and power.

Injury Prevention: Knowledge of COG can also help athletes avoid injuries. By keeping the COG within their base of support, athletes can avoid falling and losing balance, thus reducing the risk of injury.

Overall, understanding the COG and its application in sports is essential for athletes to perform at their best and avoid injury.


Friction is the force that develops on surfaces of contact of two bodies and opposes the relative motion.

Types of Friction

  1. Static Friction- the opposing force that comes into play when one body comes into contact with another body but the actual motion is not started yet
  2. Dynamic Friction- the opposing force that comes into play when one body is actually moving over the surface of another body.
    1. Sliding Friction- when the body is sliding
    2. Rolling Friction - when the body is rolling

Its applications

  • Without friction, athletes would not be able to run fast. athletes use spikes to have necessary friction while running
  • Gymnasts use lime on their palms to have friction
  • walking will be difficult without friction. imagine walking on sand
  • friction is a disadvantage for some sports like cycling.


An object thrown either horizontally or at an acute angle under the influence of gravity is called a projectile.  The path followed by a projectile is called a trajectory or parabola. There are two forces that act on a projectile- gravitational force and air resistance.

The Air Resistance of an object varies and depends on the object's shape and atmospheric conditioning in which the object is projected.

There are many examples in sports and games such as a bullet fired from a rifle during shooting, an arrow in archery, throwing a hammer, discus and javelin, etc.

Understanding the principles of projectile motion can help athletes improve their skills and performance. For example, a pitcher in baseball can adjust the angle and force of their throw to control the trajectory of the ball and make it harder for the batter to hit. Similarly, a golfer can adjust their swing to control the trajectory of the ball and make it land closer to the target.

Factors Affecting Projectile Trajectory

1. Angle of Projection: Any object released at different angles covers different distances. When the object is released at 45°, it covers the maximum distance. When it is projected at an angle of 30°, it covers less distance and when released at 60° it covers slightly more distance but less than a 45° projectile path. The angle of 45° is the best angle for achieving maximum distance.

2. Projection Height Relevant to the Landing Surface: If the height of the projection and landing surface is equal then release the object at an angle of  45°. If the height of the projection is less than the landing surface, increase the projection's angle, it should be more than 45°.  If the height of the projection is more than the landing surface then decrease the angle, it should be less than 45°.

3. Initial Velocity: If the initial velocity is more, the object covers a maximum distance.

4. Gravity: The greater the weight of the object, the greater the influence of gravity upon it. Gravity decreases the height of the projectile that it can obtain. It limits the vertical components of the projectile.

5. Air Resistance: When the object moves through the air, it is slowed down by air resistance. It decreases the horizontal component of a projectile.

Notes of Physical Education - Class 12 - Latest Syllabus

Chapter 1 - Management of Sporting Events

Chapter 2 - Children and Women in Sports

Chapter 3 - Yoga as Preventive measure for Lifestyle Disease

Chapter 4 - Physical Education & Sports for CWSN (Children with Special Needs - Divyang)

Chapter 5 - Sports & Nutrition

Chapter 6 - Test & Measurement in Sports

Chapter 7 - Physiology & Injuries in Sports

Chapter 8-  Biomechanics & Sports

Chapter 9 - Psychology & Sports 

Chapter 10- Training in Sports

Previous Post Next Post