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Objectives: ALL toDeliver PowerPoint presentation to class on:

Application of force in sportLinear, angular & general motionNewtons laws of motion (1st, 2nd & 3rd) Give examples of all above from own sport

Aims: Basic Mechanics

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Application of Force in SportSport could not occur without force e.g.:

Hitting golf ballComing out of blocks in athletics

Braking in motor sportsChanging direction (e.g. Dodging/sidestepping)Changing shape (e.g. Landing on crash mat)

3 factors need to be accounted for when considering force insport:1. Size of force2. Point of application of force3. Direction in which force acts

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Application of Force in Sporte.g. Sprinter out of blocks Part 1 = large force applied by contraction ofmuscles (larger force = greater acceleration) i.e.Size of forcePart 2 = force generated by muscles is frictionalforce occurring at point where spikes touchstarting blocks i.e. Point of application

Part 3 = friction opposes motion so as spikes pushdown/back frictional force causes sprinter to moveforward

http://www.youtube.com/watch?v=By1JQFxfLMM

http://www.youtube.com/watch?v=By1JQFxfLMMhttp://www.youtube.com/watch?v=By1JQFxfLMM

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Newtons First Law Law of Inertia

Every body at rest, or moving with constant velocity in a straightline, will continue in that state unless compelled to change by an

external force exerted upon it

i.e. An object will not change its state of motion (still or moving)unless something else (an external force) acts upon it

Examples:Sprinter running at constant speedCyclist going at constant speedSwimmer swimming at constant speedAny vehicle going at constant speedAny sportsperson standing still

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Newtons Second Law Law of Acceleration

the acceleration of a body is proportional to the force causing it, andthe acceleration takes place in the direction in which that force acts

Our sprinter should apply max possible force & accelerate to constantspeed & maintain that speed

Why then would sprinter slow down?Physiological effects e.g. Depletion of energy stores needed for

muscular contraction (ATP & PC)Effects of air resistance (very small)

Slowing down = change in velocity = deceleration100m runners tend to decelerate c.80-90mWinner may be one that decelerates least!

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Newtons Third Law Action/Reaction Law

Other sporting examples:Kicking a football 1st law states exerting force will set it inmotion; 3 rd law states ball will exert equal/opposite force onfootHigh jumper exerts force on ground for height/upwardacceleration reaction force must be more than athletesweight forcei.e. Reaction force = weight force + internal muscle force

http://www.youtube.com/watch?v=iH48Lc7wq0U&feature=related

http://www.youtube.com/watch?v=5QCj1AjlWk0&feature=fvw

http://www.youtube.com/watch?v=iH48Lc7wq0U&feature=relatedhttp://www.youtube.com/watch?v=5QCj1AjlWk0&feature=fvwhttp://www.youtube.com/watch?v=5QCj1AjlWk0&feature=fvwhttp://www.youtube.com/watch?v=5QCj1AjlWk0&feature=fvwhttp://www.youtube.com/watch?v=iH48Lc7wq0U&feature=relatedhttp://www.youtube.com/watch?v=iH48Lc7wq0U&feature=related

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Centre of Mass (COM)

Where weight of object tends to be concentrated & balancedin all directions

i.e. point where object/body balanced in all directions

e.g. Spherical objects like a shot mass distributedsymmetrically around centre (therefore its centre of mass)

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Centre of Mass (COM)Humans irregular shapes so COM harder to find

When stood upright/still COM = around navel

When we move this point changes

e.g. Arm above head moves up bodye.g. Arm adducted to right moves slightly right

COM not necessarily in actual physical matter of an object

e.g. Quoit/ring COM in hole

With athletes sometimes COM outside body e.g. Fosbury floptechnique in high jump COM outside body/underneath bar

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Activity: COM changes

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Stability & BalanceStability = ability of object to resist motion & remain at rest

More stable = more able to resist motion

Stability needed in sport to balance or for example in defensivepositions (front foot)

Factors affecting stability & balance:

Mass of the body/object greater mass = greater stabilitySize of support base larger support base = greater stabilityHeight of COM lower COM = greater stabilityNumber of points of contact with ground more points = greaterstability

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Stability & BalancePosition of COM important to maintain balance

Objects/people stay balanced if COM stays directly over base ofsupport

When COM moves away from base of support object becomes moreunstable

E.g. Gymnast on balance beam when COM moves outside beamgymnast becomes unstable & will fall!

If COM lowered or base of support increased object/body becomesmore stable e.g.:

Martial artist has wide stance to resist attackBoxer the same to stay on feet

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Types of Motion

3 recognised types of motion:1. Linear2. Angular3. General

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Linear MotionMovement of body/object in straight line

When all parts of body move same distance, in same directionat same time e.g. Waterskier

Curvilinear motion = linear motion in curved line (e.g.Shuttlecock in flight)

Occurs when force applied through COM of body e.g. Drivenpass

Force passing through COM causing linear motion = DIRECTFORCE

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Angular Motion (rotation)Occurs when all parts of body/object move in circle (or part of

circle) around fixed axis of rotatione.g. Spinning ice skater rotates about longitudinal axis

(through body from top to bottom)

Moving arms/legs when swimming/running are angular motionbecause they move about axis of rotation (joints)

Force passing outside COM of body causing angular motion isECCENTRIC FORCE

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General Motion

Combination of linear & angular motionMost common in sport

e.g. Running/swimming trunk moves linearly &arms/legs move angularly

http://www.thesunblog.com/sports/questionmark.jpg

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http://www.thesunblog.com/sports/questionmark.jpg

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Homework:

Revision for test on basic mechanics

Next Week