Human Movement

Biomechanics

Lab 3: Force SummationWhen maximum force is required:• As many contributory body pars as possible should be used• Body parts with the greatest inertia should lead the action ie the

stronger, slower muscles• Body parts should be sequentially accelerated so that each

preceding body part contributes optimally before the next body part comes into the action

• Body parts should be sequentially stabilised so that each subsequent action may accelerate around a stable base.

Equipment• Tennis balls• A large throwing area

Instructions• All activities should be performed with a partner, one throwing, and

one marking. The throw should be carried out with maximum effort. Measure using stride length. The angle of release should be kept as consistent as possible.

Activity 1

The thrower takes up a long sitting position, with their back against a wall.

The shoulders and hip must remain tight against the wall.

Throw the ball using the arm only.

Distance of throw:

Trial 1:

Trial 2:

Activity 2• Move one metre away from

the wall. • The thrower should remain

in a long sitting position. • Rotate the shoulders and

arm back as far as possible. • Do not lean back. • Throw the ball using the

arms and shoulders only.

Distance of throw:

Trial 1:

Trial 2:

Activity 3• Move two metres away from

the wall. • Stand square to the direction

of the throw. • Rotate the hips and shoulder

as far back as possible• The feet must remain in

contact with the ground and must not twist around.

• Throw the ball using the hips, shoulders and arm only.

Distance of throw:Trial 1:Trial 2:

Activity 4Record the maximum distance the ball is thrown for each activity.

Activity 1:Activity 2:Activity 3:

Did the results indicate an increase or decrease in distance? An increasing number of body parts are used in each activity.What is the principal movement action or pattern used by these body parts to develop force?

List the order in which these body parts are used in a correct throwing sequence.

Keeping in mind the principal of force summation, what observation could be made regarding the Mass of the body parts used in the throwing sequence?

Activity 5• Stay two metres away from the wall. Stand side

on to the direction of the throw, with the feet shoulder width apart and the back knee straight. Rotate the trunk as far back as comfortable. Throw the ball using the hips, shoulders and arm, but make sure the body weight has been transferred before the arm begins to move.

Distance of throw:Trial 1:

Trial 2:

During the throw, watch the action of the front leg. In order that forces can be effectively applied, this leg should stop or stabilise before the forward arm swing.

Explain why this side on position permits greaterincreases in force production.

Activity 6• Repeat Activity 5, but now step forward and throw the ball. • The back foot should be free to move or slide.Distance of throw:Trial 1:Trial 2:

Because the forward swing of the arm does not occur until the centre of gravity has ceased its forward movement and stabilised over the front foot, the momentum of this forward movement cannot contribute to the total momentum of the throw.In the throwing action how does the forward movement of the back foot assist force production?

Have the results shown a consistent increase in distance with each activity?

Motion

• Movement is the process of continually changing positions• All physical activities involve the body or implement continually changing position.

Motion is classified according to the pathway followed by the moving object:• Linear Motion (translation)• Angular Motion (rotation)• General (combination of the two)

Inertia• A body’s resistance to change in its state of motion.• The heavier an object is the greater its inertia and therefore the greater the force

required to move it or change its state of motion• For example, pushing an object – once inertia is over come it is easier to move

– Merry-go-round – feeling of moving to the outside– Car accelerating – cars front end goes up, person goes back– Car breading – cars back end goes up, person goes forward

Momentum• Mass (weight) of an object x its velocity• An object can only have momentum if it is moving. The greater the momentum, the

further it may travel and the harder it is to stop or slow down.• To increase momentum, an object must either increase its weight while retaining the

same velocity or increase its velocity.

Transfer and Conservation of Momentum• This concept is based on the knowledge that momentum can be

transferred from one body to another, or from one body part to another.

• This can happen in linear motion as well as angular motion.• The gymnast can transfer momentum into the upper body in a kip

movement on the high bar.• Parts II, III and IV shows the legs being forcefully kicked

downwards, thus transferring momentum into the upper body which is then able to rise above the bar (Newton’s 3rd Law).

• The conservation of sequential summation of force to develop maximum force is based on the transfer and conservation of angular momentum from one body part to the next.

Lab 4: Accuracy

When considering both the vertical and horizontal component of accuracy, the performer must take into account:

• The release height of the ball which controls the vertical component• The sideways alignment of the arm which controls the horizontal

component.Equipment• Tennis balls• Suitably marked wall

Activity 1• Stand 3 metres away from a wall.• Roll a ball along the floor to hit a target line at the bottom of the wall.• For this activity, the release height has stayed at the same level as it rolls

across the floor to hit the target line. This has ensured that it has struck the wall at the same height each time. The vertical component has been controlled.

Activity 2• Stand 3 metres away from a wall. • Perform several underarm pitches to the wall.• Try to hit a target line one metre above the floor.

• If you have succeeded in hitting along the target line,you have achieved accuracy in the

plane only.• If on the other hand, you have hit the wall above or below the target line, you have made an error in the

plane only.• The vertical component of accuracy is controlled by the

techniques employed in the principle flattening the Arc.

Activity 3• Stand beside a wall or blackboard. Extend an arm behind

you and put the chalk against the blackboard. Keeping the arm straight, draw an arc on the board. Number the arc 1.

• Repeat the activity, keeping the chalk in the same starting position. This time take a large step forward onto a straight leg and transfer the body weight onto the front leg before you draw the arc. Number the arc 2.

• Repeat the second activity, but step forward onto a bent knee. Number the arc 3.

• Repeat the third activity, but finish with a follow through, keeping the hand travelling in the desired direction of the force. Number the arc 4.

• Draw and label the shape for each arc in the space provided.

• Compare activity 1 and 2. What effect, if any did the step have in flattening the arc?

• Which arc is the flattest?• Could the basic techniques used to obtain

accuracy in a softball pitch be used to obtain accuracy in a baseball pitch?

• What special contribution does the arm make to the flatness of the arc in a baseball pitch?

Activity 4• Stand three metres from a corner in the gym with your

throwing shoulder against the wall. • Perform an underarm throw releasing the ball at various

heights. Make sure the arm is tight against the wall throughout the swing and to the point of release.

• In this task the direction of the arm swing has been kept consistent, therefore no sideways movement of the arm during the swing, or the ball after release should be observed. The ball should have struck the wall at various heights along a perpendicular line almost coinciding with the corner line of the gym. Therefore the horizontal component of accuracy has been controlled.

Activity 5• Stand three metres from a wall and perform several underarm

pitches to hit a target line on the wall.• If you have succeeded in hitting along the target line you have

achieved accuracy in the plane only.

• If on the other hand you have hit the wall to either side of the target line you have made an error in the

plane only.• When you achieve perfect target accuracy, you have successfully

combined the vertical and horizontal components of accuracy.

• If a cricketer bowls a wide delivery, what is the error in technique that has occurred?

• In maintaining a good bowling line in cricket, why should the bowler ensure that the shoulders rotate in the vertical plane?

Aim:To examine the type of motion produced when a force is applied to a ruler and a coin.

Equipment: • 2 x rulers• $2 coin• Sticky tape Activity 1• Place a 30cm ruler flat on the table so that the long side is 5cm from and

parallel to the edge of the table in front of you.– Gently flick the ruler at the 0cm mark– Observe and record in the table the type of motion produced– With a second ruler, measure the distance from the middle of the flicked ruler

(15cm mark) to the edge of the table– Record the result– Repeat the activity at the 10cm, 15cm, 20cm, and 30cm mark for each trial– Ensure that the same force is used for each trial

Distance from 15cm mark to edge of table

Direction of spin(eg clockwise)

Magnitude of spin (eg fast/slow, small/large)

0cm

10cm

15cm

20cm

30cm

• For the 30cm ruler flick, where can the centre of gravity be found?

• How did you determine this point?

• Was the direction of the spin the same for each trial? Yes/No.

• Give reasons for your answer.

• At which point(s) did the application of force to the ruler move its 15cm mark the furtherest?

• Why was the best result achieved there?

• Is there any similarity between your answer a and e and f? Yes/No.

• If so, outline the similarity.

• Describe the sporting situations where it is essential to apply force through the centre of gravity of an object?

Activity 2• Tape a $2 coin to the top of a ruler at the 5cm mark (don’t

put tape under the ruler)• Repeat the procedures from Activity 1, but flick the ruler at

0cm, 10cm, 20cm and 30cm marks in turn• Record the type of motion produced and the distance

travelled at the 15cm mark for each trial• By trial and error, find the mark on the ruler which, when

flicked, produces minimum rotation and maximum distance travelled at the 15cm mark

• Record the result

Distance from 15cm mark to edge of table

Direction of spin(eg clockwise)

Magnitude of spin (eg fast/slow, small/large)

0cm

10cm

15cm

20cm

30cm

cm Little or no spin Little or no spin

• What difference did the coin make to the ruler?

• Where is the centre of gravity on the ruler in this activity?

• How was this determined?

• Is the position of the centre of gravity the same as it was in Activity 1? Yes / No

• Outline the main differences between the action of the ruler (ie its direction and its spin) in Activity 1 and 2.

• Was the greatest amount of spin achieved at the same point in Activity 1 and 2? Yes / No.

• Give reasons for your answer.

• Describe sporting situations where force is applied to an object through the centre of gravity in a similar position.

• Describe the motion of the ruler when force is applied at the end of the ruler with the coin taped to it.

• Describe the motion when force is applied to the other end.

• Describe sporting situations where force is applied deliberately to achieve similar motion.

Rotational MomentumChanges in rotational momentum can be affected by two things:

• Increases or decreases in rotational speed• Changes to the distribution of mass around an axis point -=

changes to rotational inertia.

L = IwWhere L = rotational momentum

I = rotational inertiaw = rotational speed

• A diver performing a forward tuck somersault cannot change the rotational momentum of the body after take off – there is nothing to push against in mid-air – rotational momentum can only be increased if you have something to push off Eg. A vaulting horse.

• The rotational inertia can be changed mid-air = change in rotational speed

Conservation of Rotational Momentum

• Some rotational momentum is lost due to air resistance – not much

• For all intensive purposes it is conserved until a force is applied to change it – it will stay the same unless something is dome to change it (push off the vault = increase, hit the ground = 100% decrease).

Lab 6: ProjectileAim: • To examine the effect that altering the following has on the

distance a projectile travels:• Force of projection• Angle of release• Height of release

Equipment:Activity 1 and 2• Tennis ball• 25m tape measure• marker• large wooden protractor (optional)Activity 3• Above plus a chair

Activity 1 – Force of projectionMethod – Part A• A person stands at the 0 metre mark. The non throwing arm is

raised at an angle of 45 degrees to the horizontal.• A tennis ball is held close to the chest, with the elbow away from

the body.• The ball is then ‘pushed’ hard away in line with the non throwing

arm• A partner measures the distance from the 0 metre mark to where

the ball hits the ground• Repeat a further two times and record results.

Method – Part B• Repeat the above procedure, but this time only bring back the ball

level with the elbow before ‘pushing’ ie give it ‘half a throw’• Measure the distance covered in flight and record the results in the

table below• Repeat a further two times

Discussion of Activity 1:

• Which action achieved the greater distance?

• Outline results for this result.

• Complete the following principle: “The the force of projection or speed of release, the

will be the distance travelled”

• Describe a sporting situation that uses this principle.

Activity 2 – Angle of releaseMethod – Part A• Use the same procedure as in Activity 1 Part A, but this time

stretch the non throwing arm out horizontal in front of the body• This position is 0 degrees• Project the tennis ball in line with the non throwing arm, measure

the distance covered in flight and record the results in the table• Repeat a further two times and record results.

Method – Part B• For projection at an angle of 45 degrees, re-record your results

from Activity 1 Part A in the table• Method – Part C• Repeat the above procedure with the non throwing arm raised to

80 degrees and the ball projected in line with it• Again perform all three trials and record the results.

Discussion of Activity 2:

• Was the ball released with the same force (at the same speed) each time? Yes/No.

• Ignoring distance, which of the three angles had the greatest horizontal component of velocity?

• Which angle had the greatest vertical component?

• At which angle of release was the distance covered greatest?

• Outline the reasons for this result.

• What advice would a long jump coach give the jumper to get the better results?

Activity 3 – Height of ReleaseMethod – Part A• Use the same procedure as in Activity 1 Part A ie

the non throwing arm is held at 45 degrees. For this part of the activity, stand on a chair or bench.

• Measure the distance covered in flight and record the result.

• Repeat twice more.

Method – Part B• For projection with your feet on the ground, re-

record your results from Activity 1 Part A

Discussion of Activity 3

• What height (chair, ground) achieved the greater distance?

• Outline the reason for this result.

• Complete the following principle: “the the height of release, the will be the distance travelled”

• Describe 3 sporting situations that use this principle.

Table of ResultsTrial 1 Trial 2 Trial 3 Trial 4

Force of projection

a.Full throw

a.Half throw

Angle of release

a.0 degrees

a.45 degrees

a.80 degrees

Height of release

a.From a chair

a.With feet on the ground

Projectile motion

• As soon as an object or body is released into the air, it becomes a projectile.

• A projectile can have a range of different trajectories or flight pats depending on the nature of the activity.

• A projectile is automatically under the influence of gravity and air resistance as it travels through the air.

Range of trajectories for various sporting activities

Factors affecting the flight path of a projectile motionApplication of force• The force applied to the projectile will largely affect its motion• The force can vary in its amount as well as its direction of application• The greater the force applied to the projectile the further the projectile will

travel

Angle of release• In most sporting situations, where the maximum distance of a projectile is

desired, there needs to be an accurate angle of release, to maximise the effects of gravity and air resistance.

• Where optimal distance is required, the optimal angle of release is 45°.• Any deviation from this optimal angle will result in reduced distance.• There are some situations that require the release angle to be more or less

than 45°.• In long jump too much horizontal distance would be lost at this angle so a

lower angle of take off would be more beneficial.• The opposite would occur in high jump where vertical distance is the aim.

Height of release• If the angle of release and speed of release were constant, an

object released from a higher point, such as a cliff top, would travel further than an object released from ground level.

• This can be seen at a golf course where the tee is at the considerable higher level than the green.

• In this situation the golfers have the opportunity to hit the ball greater distances than if the tee was situated on a lower level.

• This is due to the extra flight time the ball experiences before it falls all the way to the ground.