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When A Sprint Race Is About To Start, A Sprinter Stands Still Bracing His Feet Against

The Starting Block. To Break This Stillness, The Sprinter Has To Exert Some Influence.

The Influence That Breaks The Stillness Is A Force. The Force That Breaks The

Stillness Of The Sprinter Is The Force Of The Reaction That Is Produced Because Of The

Pressure Exerted Against The Starting Block By The Sprinter. (Figure 3.3)

When The Ball Is Coming Towards A Batsman, He Hits It With His Bat To

Change The Direction Of Motion Of The Ball By Exerting Some Force On It.

The Force Necessary For A Sportsman For Motor Activities Is Generated By The Contraction

Of His Muscles.

When An Athlete Is Throwing, The Shot Put, He Must Exert Some Force On It In Order

To Make It Move. Further, That Force Must Be Exerted In The Direction In Which The

Shot Put Must Be Thrown.

Figure 3.3

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For Extra Knowledge

The First Law Of Newton That You Learnt In Science Is As Follows:

''Until An Unbalanced Force Is Applied On It, Bodies At Rest Remain

Stationary And Bodies In Motion Continue To Move At Uniform Velocities.''

Apply The First Law Of Newton To The Example Given Above.

Direction Of Force

A Force Has Both A Magnitude And A Direction. Direction Of Force, Too, Has An Effect

On Actions. When Illustrating The Direction Of Force By Drawing A Line, The Length

Of The Line That Is Drawn To Scale Is Reflective Of The Magnitude Of The Force And The

Direction In Which The Force Is Acting Is Indicated By The Direction Of An Arrow Head.

A Weightlifter Exerts An Upward Force To Lift A Weight. Then That Object

Moves In The Direction In Which The Force Is Exerted. (Figure 3.4)

Figure 3.4

When An Athlete Jumps Up, The Ground Exerts A Force Vertically Upwards On The

Athlete Because Of The Force That The Athlete Exerts On The Ground. That Means The

Force Acts In The Direction Of The Motion.

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For Extra Knowledge

Recollect The Third Law Of Newton That You Learnt In Science.

“For Every Action, There Is An Equal And Opposite Reaction.”

Apply The Third Law Of Newton To The Example Given Above.

Momentum

Momentum Is A Measure Of How Difficult It Is To Stop The Motion Of An Object In

Motion.

When Playing ˝Elle˝ It Is Easy For You To Catch The Ball That A Player Throws At You,

But If A Heavier Object Is Thrown At You, It Would Be More Difficult For You To Catch It.

Further, Even An Object That Is Not So Heavy Would Be Difficult To Be Caught When It

Is Moving Very Fast.

Accordingly, Momentum Depends On The Mass And Velocity Of An

Object.

The Momentum Of A Shot Put That Is Rolling Over Fast Is Greater Than The One That Is

Rolling Over Slowly. Further, The Momentum Of A Bigger Shot Put That Is Rolling Over

At A Certain Speed Is Greater Than That Of A Smaller One That Is Moving At The Same

Speed.

When A Cricketer Catches The Ball Coming Towards Him, He Exerts Some Force On The

Ball With Both His Hands In Order To Stop The Ball (Figure 3.5). Then The Momentum

Of The Ball Becomes Zero As Its Velocity Becomes Zero And Consequently The Ball

Stops Moving.

Momentum = Mass X Velocity

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Figure 3.5

Effects Of Principles Of Biomechanics On Activities

Walking

The Purpose Of The Activity Of Walking Is To Carry The Body From One Place To

Another. While Walking, The Body Moves Forwards Or Backwards And The Weight Of

The Body Is Shifted From Foot To Foot Alternately. Accordingly Walking Is Called An