AREA OF STUDY 1 - HOW ARE MOVEMENT SKILLS IMPROVED?

Unit 3 – Movement Skills and Energy for

Physical ActivityAREA OF STUDY 1 - HOW ARE MOVEMENT SKILLS IMPROVED?

Biomechanics –

Equilibrium and Human Movement

Equilibrium

Equilibrium:

A state in which opposing forces are balanced.

A state in which all forces cancel each other.

Static Equilibrium:

When an object is stationary and all the forces or torques acting on it total to zero.

Dynamic Equilibrium:

When an object is moving with constant velocity and is not changing its state of

motion (speed nor direction).

Equilibrium

Balance:

The ability to maintain and control equilibrium.

Stability:

Having a high degree of equilibrium and being able to resist change.

Stability

In most sports the ability to control and manipulate stability is critical to successful performance.

In some activities, the athlete tries to increase stability to improve performance :

For example: wrestling, batting, archery stance.

In other activities, the athlete tries to decrease stability to improve performance :

For example: sprint start, gymnastics tumbling.

Stability

Factors affecting stability include:

height of centre of gravity

alignment of centre of gravity

area of base of support

alignment of base of support

friction

mass

velocity

Factors Affecting Stability

The concept of “centre of gravity” is important when trying to understand balance.

Centre of gravity is the point of balance of an object.

For athletes participating in sport the centre of gravity :

is inside the pelvis just in front of the sacrum.

is slightly higher in males.

can vary according to body position.

Alignment of Centre of Gravity

If the line of gravity is over the base of

support, stability will be maintained.

When the line of gravity falls outside

of base of support, an athlete will lose

stability and fall over.

For example in the sprint start athletes will

align their centre of gravity outside their

base of support to make a quick start.


Area of Base of Support

The bigger the area of the supporting base,

the greater the stability.

This is because the distance that the centre

of gravity can move before it falls outsidethe base of support is increased.

An athlete wanting to increase stability will

spread their legs to increase the area of

the base of support.


Alignment of the Base of Support

To increase stability the base of

support should be aligned in the

direction of oncoming forces.

For example, a footballer about to be

tackled or a boxer about to be

punched will spread their legs in the

direction of their opponent.


Friction

Stability will be increased when the friction

between the athlete and the contact

surface is increased.

Examples:

wax on a surfboard

athlete’s spikes

footballer’s boots


Mass

A body with a larger mass will be more stable as it has greater inertia (tendency

to resist changes in state of motion), and

will require a greater force to move it.

For example a sumo wrestler is hard to push

out of the ring.


Tips for Increasing Stability

Spread your legs to increase the size of the base of support.

Align your base of support in line with oncoming forces.

Crouch down to lower your centre of gravity.

Place your centre of gravity over the base of support.

Shift your centre of gravity towards oncoming forces.

Increase friction between you and the ground.

Put on weight !

Be on the move.

Levers

A lever is a rigid bar that allows the application of increased “FORCE” and/or

“SPEED”.

All levers have common parts :

an axis (point of rotation)

a resistance (load to be overcome)

a force (effort) FORCE

AXIS

RESISTANCE

First Class Levers

In first class levers the “axis” is between the

force and resistance.

FORCE

AXIS

RESISTANCE

F AR

Rowing

F

A

R

Scissors

Second Class Levers

In second class levers the “resistance” is

between the axis and force.

FORCE

AXIS

RESISTANCE

F

A

R

F

A

R

Bottle opener

Wheel barrow

Third Class Levers

In third class levers the “force” is between the axis

and the resistance.

RESISTANCE

AXIS

FORCE

F

A

R

F

A

R

Kicking a ball

Bicep curl

Levers

The Principle of Leverage

That the velocity is greater at the

end of a long lever than at the end

of a short lever.

OR

That the further a point of a lever is

from the axis then the greater its

velocity.

F

A

R

Kicking a ball

A 3 iron will hit the ball further

than a 9 iron.

The arm & racquet

should be fully

extended at impact.

The leg should

be fully extended

at impact when

kicking a ball for

distance.

A baseball batter

should grip the bat at

the end of the handle to make the

bat as long as possible.

Revision Questions

1. When a body is at rest and all forces on it total zero, it is in a state of :

a. dynamic equilibrium.

b. static equilibrium.

c. mobile equilibrium.

d. gravitational equilibrium.

2. A baseballer widening the base of support and aligning it in the direction of the pitch is anattempt to :

a. decrease stability

b. increase stability.

c. psych out the pitcher.

d. see the ball better

3. A sprinter using blocks to enable a crouch start is an attempt to :

a. decrease stability.

b. increase stability.

c. decrease friction.

d. overcome gravity.

4, Centre of Gravity :

a. is the point of balance of an object.

b. of a gymnast can be altered if the body position is changed.

c. can fall outside the mass of an object.

d. all of the above.

Revision Questions

5. An increase in mass will :

a. increase stability.

b. decrease stability.

c. have no affect on stability.

d. none of the above.

6. Which of the following is an example of

increasing stability ?

a. a gymnast raising both arms above the head.

b. a boxer fasting before the fight.

c. a skier bending the knees.

d. a sprinter forming a crouch start.

7. An increase in friction will :



c. have no effect on stability.


8. An increase in momentum will :



c. have no effect on stability.


Revision Questions

9. The two main functions of levers are to :

a. increase force and decrease speed.

b. increase force and increase speed.

c. decrease force and decrease speed.

d. decrease force and increase speed.

10 Which of the following is NOT an example of a

first class lever ?

a. bottle opener.

b. scissors.

c. see saw.

d. crowbar.

11. A wheelbarrow is an example of a :

a. first class lever.

b. second class lever.

c. third class lever.

d. fourth class lever.

12. In kicking a football the lower leg acts as a :

a. first class lever.

b. second class lever.

c. third class lever.

d. fourth class lever.

Revision Questions

13. Outline how a tennis player can maximise the

force produced when serving the ball.

Answer: - have the arm fully extended, holding

the end of the grip on contact.

14. Give four examples of leverage in sport.

Answer: - cricket bat, hockey stick, tennis

racquet, bowling arm, kicking leg.

.

15. In simple terms a number 3 iron will hit the ball

further than a 9 iron when playing golf. Neglecting

the influence of the angle of the club head, why is

this so?

Answer: - a 3 iron is longer than a 9 iron so the club head will travel faster on a 3 iron. A faster club head speed will mean faster ball speed and greater distance.

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AREA OF STUDY 1 - HOW ARE MOVEMENT SKILLS IMPROVED?