Biomechanics U2

Includes: Balance and stability, laws of motion, projectile motion, and levers

Newton's First Law

An object at rest stays at rest or in uniform motion stays in motion unless acted upon by an external force.

Example of external forces acting on objects

Muscles, wall stopping a ball air resistance (wind), gravity, friction

Newton's Second Law

When a force is applied on an object the object will accelerate in the direction that the force is applied, directly proportional to the size of the force and inversely proportional to the objects mass.

Equation for Newton's second law

Force=Mass x acceleration

Therefore…

Acceleration= Force/mass

Mass= Force/acceleration

When force increases:

acceleration increases

When force decreases

Acceleration decreases

When mass increases (force stays equal)

Acceleration decreases

When mass decreases (force stays equal)

Acceleration increases

Newtons 3rd law

For every action there is an equal and opposite reaction

When answering questions about newtons 3rd law what should you include?

Action force/reaction force

How to structure ALL biomechanics questions

D- Definition

E- Equation

E- Explanation

P- Performance link (causing them to go faster, causing them to power ahead of the other rider, etc)

Define momentum:

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

Formula for momentum

Mass (weight of the body) x velocity (speed something is going at)

What is conservation of momentum?

References the idea that a projectile/body will continue in motion unless acted upon by an external force.

• Total momentum of 2 bodies prior to impact is equal to the total momentum after the impact (no energy lost in the collision)

What is force summation?

Force summation is the correct timing and sequencing of body segments to produce a maximal force.

Eg: Trying to throw a ball as far as possible.

BEST acronym to remember when thinking of ways to maximise force summation:

1. use as many Body parts as possible

2. sEquence- move heavier/slower (more mass, less velocity) body parts such as legs and trunk, followed by lighter/faster (more velocity, less mass) body parts such as the arms and fingers.

3. Stabilization- Body parts must stabilize so momentum is not lost.

4. Timing- move the next body part only once the previous body part has reached maximum velocity.

5. Follow through with movement

What is impulse?

Impulse is a measure of change in momentum in a body.

Formula for impulse

Impulse=Force (how hard a ball is thrown) x time (how long the ball is in the air)

How can impulse (momentum changing) occur?

By speeding up and object or slowing it down (Stopping/breaking momentum, or starting/making momentum)

What is force reception?

Force reception is when we try to safely stop the momentum of a projectile, and take the objects momentum from whatever it starts at (decided by momentum maker), to 0.

How do we decrease force reception/reduce force?

To reduce the force reception of an object, we must extend the time over which we recieve the force.

• This means that although impulse remains the same (original momentum--->0), we are increasing time, which means the force must be decreased.

How do we increase force reception/ increase force

To increase force reception of an object, we must shorten the time over which we recieve the force.

• This means that although impulse remains the same (initial momentum--->0), we are decreasing time, which means force must be increased accordingly.

Why can we increase impulse as a momentum maker but not as a momentum breaker?

We can increase impulse as a momentum breaker as we are the ones deciding how much mass and velocity to put on the ball, which could mean that an object goes from 100-0 (bigger impulse) or 5-0 (smaller impulse) depending on the momentum we give it. As a momentum breaker, all we can control is how much force we receive by extending or decreasing time (Impulse is constant, unchangable)

How do we increase impulse?

We can increase impulse in 2 ways:

1. Increase Force (Get Stronger) You train your muscles to apply a massive amount of force in a split second.

2. Extend time over which force is applied. (Increase time) If we increase time in which force is applied over, we will create a larger impulse (Force x time), and will be able to summate more force (BEST).

What is the main technique we can use to extend time over which force is being applied?

By following through the action (Eg: tennis)

What is angular momemtum

Movement around a central axis

Equation for angular momentum

Moment of inertia (mass times radias squared) x angualr velocity

What is an eccentric force?

A force that does not act in a line that passes through the centre of mass of an object, causing it to rotate.

This causes a turning effect, known as a tourque.

Moment arm

Distance from the object's centre of mass---> the point in which the force is applied.

A larger moment arm will cause an object to rotate more.

What is a tourque?

The turning effect of an eccentric force applied to an object.

Equation for tourque

Force (how much pressure is applied) x moment arm (distance fromt he objects centre of mass.)

Difference between angular momentum and tourque?

Angular momentum refers to the amount of rotational motion a body has, compared to torque, which is what CAUSES the object to start rotating. (Torque is the force; angular momentum is the turning effect)

What is angular velocity?

The speed at which an object is turning at

What is moment of inertia?

The tendency of a body to maintain a state of angular motion, resistance to changing this state.

What happens to angular momentum when force and moment of inertia differ?

Whilst the moment of inertia may increase or decrease, causing angular velocity to increase or decrease accordingly, angular momentum will stay relatively the same, as when one factor increases, the other decreases (cancels)

Why is it important that kids find a lighter cricket bat to play with?

Because they have a small amount of strength, meaning that if they try to swing a large bat, they will be able to generate minimal velocity, meaning they must find a 'sweet spot ' with a bat that they can swing with enough force.

What is conservation of angular momentum?

Once airborne, angular momentum is maintained, meaning a spinning body will continue to spin indefinitely, unless an external force acts upon it.

• This means that whilst angular velocity and moment of inertia increase and decrease, angular momentum will not change until acted upon by a force such as a wall, water, etc.

What is displacement?

Physical distance from the start point to the end point.

Eg: If we run around an athletics track for 4 kms, our displacement wil be 0.

What is distance?

The length of a path between 2 points that we cover.

Eg: if we run around an athletics track for 4kms, or distance will be 4km

Positive acceleration

speeding up

Negative acceleration

slowing down

Define equilibrium

A state where all forces and torques are balanced.

When may equilibrium occur?

When we are standing still or moving at a constant velocity.

Define stability

The resistance to a change or disruption of equilibrium.

Define balance

The ability to control and maintain equilibrium

Name 3 factors that influence stability

1. Area of base support

2. Position of centre of gravity

3. Line of gravity

What is area of base support?

• The area that is bounded by body parts in contact with the surface.

-The larger the base, the greater the stability

Eg: Sumo wrestlers have greater stability and therefore greater resistance to a disruption in equilibrium than ballerinas, since they have a larger base of support.

Position of centre of gravity

This is a theoretical point through which the weight of an object appears to act.

• This point lies around our hips, but changes as we move.

• A lower centre of gravity increases our stability, which makes it harder to disrupt our equilibrium.

• To lower our centre of gravity, we must squat/bend our legs.

Line of gravity

This is a theoretical line drawn from our centre of gravity to the base of support.

• If we lean forward without moving our feet (base of support), our line of gravity goes outside our base of support, making us unstable.

• This is important for sprinters so that they can react quickly (become unstable and disrupt equilibrium quickly)

What is a lever?

Levers are a rigid bar used for assistance.

Why are levers used?

Levers are used to increase the force applied to move a weight.

3 things all levers have

1. Axis

2. Resistance-(weight or load) that is moved.

3. Force- (effort) required to move the resistance

1st class levers

Axis is in the middle of the lever. (seesaw)

2nd class lever

Resistance is in the middle of the lever

3rd class lever

Force is in the middle of the lever

Define mechanical advantage

Mechanical advantage is the measure of how much a lever can amplify force or speed.

Formula for mechancial advantage

Resistance arm divided by force arm

Resistance arm

The distance from the resistance (load), to the axis (where the lever is pivoting)

Force arm

The distance from the force (effort), to the axis (where the lever is pivoting)

How can we increase the resistance arm? How does this benefit us?

• We can increase the resistance arm by straightening our arms or legs, and using a longer lever.

• This means that the distance from the resistance to the axis is much longer, decreasing the mechanical advantage further below 1, therefore generating greater speed and an increased RANGE OF MOTION, however less force.

How can we increase the force arm? How does this benefit us?

• We can increase the force arm by bending our arms or legs, and using a shorter lever.

• This means that the distance from the resistance to the axis is much shorter, decreasing the mechanical advantage further above 1, therefore generating greater force and a decreased RANGE OF MOTION, however less speed.

How to structure a mechanical advantage question:

D- Define mechanical advantage

E- Equation

E- Explanation (include what 3rd class levers are used for, reistance arm, decreased further below 1.

P- Performance link (GREATER RANGE OF MOTION, throw further, not as far, etc.)

Example of structuring a mechancial advantage question: Using knowledge of mechanical advantage, explain why a mechanical advantage of below 1 is beneficial for a hammer thrower.

1. Mechanical advantage is a measure of how much a lever will amplify force of speed.

2. , and is calculated by resistance arm divided by force arm.

3. The hammer is a 3rd class lever, and is used to produce speed.

4. By straightening the arms and using a longer hammer, the thrower can increase their resistance arm, therefore decreasing the mechanical advantage durther below 1.

5. This increases the range of motion of the hammer, and produces a greater speed, allowing the thrower to throw further.

Projectile motion

the curved path that an object follows when thrown or launched in the air.

Vertical component of projectile motion

Refers to the height reached and flight time of a projectile

This is influenced by gravity

Horizontal component of projectile motion

Refers to the horizontal distance covered by a projectile

This is influenced by air resistance (wind)

3 factors of projectile motion:

H- Height of release

A- Angle of release

V- Velocity of release

What is the height of release?

The height of release is the difference between the height a projectile is released from and the height in which it lands/stops.

What is the angle of release?

The angle of release is the angle the object is projected into the air at.

• This is dependent on the objective of the sport.

How do height of release and angle of release interact?

If we increase the height of release, the angle of release decreases, allowing us to hit a ball faster, but not as far.

If we decrease the height of release, the angle of release increases, allowing us to hit a ball slower, but achieve a greater distance.

Height of release higher than landing height: Optimal angle of release will need to be smaller to maximise horizontal distance.

Height of release is lower than landing height: Optimal angle of release needs to be bigger to maximise horizontal distance.

What is the velocity of the release?

This is the speed at which an object is thrown, kick or propelled into the air at.

The greater the speed of release, the greater horizontal range of the projectile.

What is a skill?

The ability to do something well.

What is a motor skill?

A voluntary, goal directed activity that we learn through practise and experience. Motor skills are a special form of skill that require movement of the body or limbs to achieve a goal.

Name the 2 types of motor skills

• Gross motor skills

• Fine motor skills

Gross motor skills+example

Involves the recritment of larger muscle groups, or uses the whole body.

Eg: Serve, drop punt, somresault

Fine motor skills+example

Involves recruitment of smaller muscle groups, such as hands, and does not use the whole body.

Eg: Hand movements in dance, chess, darts.

3 stages of learning a skill

Cognitive stage (beginning stage)

Associative stage (practise stage)

Autonomous stage (automatic/advanced stage)

Cognitive stage of learning (understanding)

The beginner makes large errors

They make frequent errors

They are unable to detect their own errors.

What learners in the cognitive stage need to do to improve their skills

• Few simple instructions at a time

• Demonstrations are best

• Break complex skills into smaller parts

• Lots of practise

• Positive/constructive feedback

• Focus on mastering fundamental movement skills

Associative stage of learning (practise)

The learner makes slightly smaller errors

They make less frequent errors.

They are able to correct majority of their errors.

What learners in the associative stage need to do to improve their skills.

•Regular feedback to refine skills and reduce chance of poor habits developing

•Opportunities to practise with increased variability (more random and more open)

Autonomous stage of learning (automatic)

The learners make very few, tiny errors, and are able to straight away detect and correct their errors.

What learners in the autonomous stage need to do to improve their skills

•Practice under game-like conditions to focus on tactics, shot selection

•Practice opportunities with a high level of variability, open environment

•Practice that challenges each athlete to use higher-order thinking via a range of problem-based learning scenarios

3 types of movement in a skill

Discrete skills

Continuous skills

Serial skills

Discrete skills

These skills have a distinct beginning point and end point.

Example: A baseball throw, a football kick

Continuous skills

These skills have no distinct beginning or end.

Example: Driving a car, swimming, running

Serial skills

Serial skills string together several discrete tasks to form a continuous performance.

Example: Tennis serve, dance routine

2 classifications of skills

Open, closed

How to classify a skill

Skills can be classified depending on:

• Stability of the environment- Stable or unstable (are there defenders, ski slopes, wind, etc.

• Timing of the skill- internally or externally paced (do you get to choose when to perform the skill?)

• Inter-trial-variability- Is the skill performed the same or differently each time?

Open skills

• Open skills are performed in an unstable environment, are externally paced (that is, the timing of the skill being performed depends on factors external to the performer), often meaning the performer has to make a split second decision, and have high inter-trial variability (that is, the skill is performed differently each time).

Examples of open skills:

Kicking a ball in play in soccer

• There is an unstable environment since there are defenders

• The skill is externally paced by defenders providing pressure, meaning you must make a split second decision

• There is high inter-trial-variability, meaning that each time you perform the skill it must be performed differently, since sometimes you kick the ball further, apply more/less force, etc.

Closed skills

Closed skills are performed in a highly stable environment. They are internally paced and so the performer is in full control of the timing of the movements and there is low inter-trial variability, so the skill is often performed the same each time.

In such an environment the performer goes through a pre-learned motor program without having to consider environmental changes and without the stress of quick responsive decision making.

Examples of closed skills: diving, gymnastics, archery, set shot for goal in AFL and shot put.

2 types of practise strategies

Whole or part

Whole practise

Whole practice is the learning of skills in their entirety.

This is where the whole skill is practised.

If the skill is simple, whole practice is generally recommended

Skills such as hitting a softball or shooting an arrow are generally taught as a whole as the skill occurs in one continuous movement (you can’t break these skills down)

Part practise

Part practice is the learning of skills broken down into parts.

Part practice is most effective when the skill to be learned is complex and has clearly defined components.

A tennis serve would be taught as part practice where parts of the skill are independent of each other. In this case – Grip, foot position and swing would be taught separately from each other. (You could learn how to toss the ball into the air first)

Types of distribution of practise

Mass or distributed

Massed practise

Training sessions are longer in duration but less frequent

Suits non-professional, social athletes that also need to prioritise other tasks.

Eg: Local footy team training twice a week for 3 hours.

Distributed practise

More frequent but shorter training sessions.

Suits athletes who are professional, and are able to dedicate all their time to the skill.

Eg: AFL team training 5 times a week for 75 minutes

How is distributed practise used in a training session?

•Learners will have more frequent breaks, with opportunities for feedback from a coach and teammates.

This suits cognitive learners (beginners) attempting to grasp a new skill

How is massed practise used in a training session? What are the advantages of mass practise?

Continuous practice with little or no rest between repeat rehearsal of skill in the training session.

Advantages:

• Mass practise maximises practise time, and suits a highly motivated performer.

• It also suits practising non-fatiguing, discrete skills.

Disadvantages:

• Physically and mentally fatiguing

• Involves lots of repetition, may become boring.

How is distributed practise used in a training session? What are the advantages of distributed practise?

More frequent breaks, with opportunities for feedback from a coach and teammates.

This suits cognitive learners attempting to grasp a new skill

Advantages:

• Encourages greater learner engagement

• Assists beginners and unmotivated perforomers

• Reduction of mental and physical fatigue during practise

• Suitable when learning a complex skill.

• Recovery allows memory consolidation

Disadvantages:

• More time comsuming.