Kinetic concepts of human movement

Question 1

Biomechanics

Answer 1

The science that studies living things from a machanical perspective.
Uses principles based around motion and forces to assist in developing and refining human movement.

• kinetics studies motion and the forces that underlie this motion.
• Kinematics is solely focused on the study of motion and does not take into account any forces that may be acting upon the body in motion.

Question 2

Movement analysis

Answer 2

Could be quantitative (numbers and data) or qualitative (subjective, observationsal information)

e. g 200m sprint:
quantitative: use of timing gates every 20m could provide feedback on their reaction time, acceleration and maintenance of speed across race.

qalitative: an observation as you were slow off the blocks or around the bend

both are useful, where:
quantitative is used more in a lab setting, providing specifc data
qualitative is used more in day to day by coaches or physical educators.

Question 3

Force

Answer 3

defined as a push or a pull.
e.g gravity acting on an object, someone kicking a ball or muscles pulling on a bone.

Force = mass x acceleration (f=ma)

Forces can impact objects in two ways:

1. change the shape of an object (stretch, squash or twist)
2. move the object (move from rest, speed up or down or change direction)

force is measured in newtons which is the amount of force to move 1kg of mass at 1m/s2

Question 4

TYPES OF FORCE (Friction)

Answer 4

Occurs when two surfaces are in contact with each other. It opposes the motion of an object.

Question 5

When is friction increased/decreased in sport

Answer 5

• increased: studs in footy (increased surface aera) chalk in gymnastics (increase friction between bar and hands) grips on cricket bats
• decreased: down hill skiing wax on skies to reduce fricion, lubricant on chain decreases friction on bike chain.

Question 6

Friction principles

Answer 6

• to start an object moving across a surface, the friction must be overcome by applying an increasingly greater force. As the applied force increases, so does the friction to an extent.
• the max amount of friction that can be generated between two non-moving surfaces is called maximum static friction.
• if the applied force increases beyond the maximum static friction, the object will begin to move.
• the greater the mass of an object, the more friction and therefore greater force required to move it.

Question 7

Air and water resistance - Drag force

Answer 7

When an object or body moves through air or fluid a drag force will be experienced.

Drag force opposes the direction of motion of the object slowing it down.

drag is affected by:

• air density
• cross sectional area of the body
• speed of object (greater speed= greater force)

Question 8

how can drag be minimised

Answer 8

• technique (manipulating body position) (tuck on bike, torpedo in swimming
• clothing (fabric and design) (tight bathers when swimming, teardrop helmet in cycling)

Question 9

Newtons first law of motion: inertia

Answer 9

an object will remain at rest or in a constant state of motion unless acted upon by an external force.

e.g golf ball would continue straight if gravoty (external force) didnt bring it back to the ground.

soccer ball would not move until a player kicks it.

a heavier weight= greater inertia

Question 10

Gravitational force

Answer 10

Is a downward force that acts on all objects on earth

the accerlation of gravity on earth is 9.8 m/s

Question 11

Weight / mass

Answer 11

mass is the amount of matter that makes up an object (kg)

weight= mass x gravity (measured in newtons)

if gravity was higher mass remains unchanged, but weight would change

Question 12

Momentum (and examples)

Answer 12

the amount of motion an object has and its resistance to changing that motion.

momentum= mass x velocity

an object that is not moving, has zero momentum due to no velocity.

when two objects collide, they will move in the direction of the object with the greater momentum. Whenever two objects collide, there is a change in the momentum of each object. The mass of each object stays the same, so the chage in momentum is a result of a change in object’s velocity.

Question 13

Conservation of momentum

Answer 13

The total momentum before a collision is equal to the total momentum after a collision
in golf, before contact is made with the ball, the golf ball has zero momentum (due to zero velocity) and the club head has a high momentum. After the shot has been made the momentum will e passed onto the ball which will move off with a hig momemtum and the club will decrease to zero.

Question 14

Summation of momentum

Answer 14

Is the sequential and coordinated movement of each body segment to produce maximum velocity.

when the main objective of a sport is to hit, kick or throw an object or ball as far as possible, the object needs to be released or struck with maximum velocity.

Question 15

Principles of force summation

Answer 15

• use stronger and larger muscles first
• use as many body parts as possble so that force can be generated over more time.
• transfer momentum from one body part to another when at maximum velocity
• ensure a stable base so that momentum can be transferred from one body part to another.
• ensure appropriate follow through to prevent unnecessary deceleration of body parts

throwing examples: momentum generated in lower body is transferred to the hips and trunk, then the shoulder and elbow and finally to the wrist.

Question 16

Impulse

Answer 16

Is the force being applied and the time period over which it is applied.

Impulse = force x time

a change in the momentum of an object can result from a large force being applied over a very short period of time (softball strike) or a small force being applied over a longer period of ime (gold ball rolling over putting green)

Question 17

How is momentum decreased or increased.

Answer 17

1. increased momentum:
   - spinning in discus compared to simply standing and throwing.
   - pushing a puck in hockey instead of slapping it
2. reduce momentum:
   - giving with the ball in cricket when catching by having the hands continue to move in the direction the ball was travelling
   - bending your hips, knees and ankles when you land after jumping
   - moving with the direction of the ball when receiving a pass on the chest in soccer

Question 18

Newton’s second law of motion: Acceleration

Answer 18

The rate of acceleration of body is proportional to the force applied to it and in the direction in which the force is applied.

to produce maximal force, mass and acceleration should be at their highest (f=ma)

example: The higher the mass and the faster it can be accelerated, the higher the overall force that can be transferred to the baseball.
- What would happen if a bat that is too heavy is used? It is counterproductive to select a very heavy baseball bat if the person swinging the bat cannot accelerate it quickly enough to hit the ball
- What would happen if a bat that is too light was used? The player would be able to swing with a high level of acceleration, but due to the low mass of the bat, the force applied to the ball would be low.
- From a practical perspective, athletes need to find a balance between mass and acceleration (ie. Appropriate weight that can still be swung with high acceleration

Question 19

Acceleration

Answer 19

There is an inverse relationship between the mass of an object and its acceleration, using the formula F=ma.

• when mass is increased, acceleration is decreased
• when mass is decreased acceleration is increased.

Question 20

Newton’s third law of motion

Answer 20

For every actions there is an eqal and opposite reaction.

Whenever an object exerts a force on another object, there will be an equal and opposite force exerted by the second object on the first.

e.g When running, we push down and backward on the ground with our feet (action) and the surface pushes up and forward (reaction). This is called the ground reaction force

Question 21

third law of motion e.g

Answer 21

Consider the same individual jumping three different times:
If aim is to jump directly into the air and land on the same spot, the force must be applied directly down.
If aim is to jump up and forwards, the force must be applied down and back.
If aim is to jump up and backwards, the force must be applied down and forward
The size of the force applied to the ground determines the force applied back to the person jumping