Year 11 biomechanics with levers, force summation

BiomechanicsBiomechanicsThe study of forces and their effects on the human body

Year 11 Achievement Standard 1.2

Characteristics of motionCharacteristics of motion

Linear motion- Motion that occurs is a straight line. All parts of the body

move in the same direction and at the same speed (e.g. jumping up in the air to catch a ball or travelling in a car).

Line out jumper in Rugby Union

Drag Racing


Angular motion- Motion that occurs around an axis. This axis can be

internal (e.g. body parts rotating around a joint) or external (e.g. spinning a ball on your finger).

Spinning a ball on your finger

Spinning figure skater


General Motion- A combination of linear and angular motion. This is the

most common of all movements, as most human movement requires the rotation of body parts around joints (e.g. cycling, swimming and running).


Apply your knowledge!- Classify the following physical activities as linear motion or

angular motion or general motion.

1. Sprinting2. Rebounding a basketball3. Driving a car4. Tossing a underhand ball in basketball5. Horse riding6. Lawn bowls

Centre of gravityCentre of gravity

Centre of gravity can be defined as “the single point at which all parts of an object are equally balanced”.

For a ‘normal’ human being standing upright, their centre of gravity lies around the area of their navel.

A persons centre of gravity can change depending on their body position because as mentioned before, the centre of gravity is the exact point where all parts of an object are equally balanced.

The centre of gravity can also lie outside an object, especially if the object is bent over or leaning in a certain direction


= Centre of gravity

Centre of gravity for a “normal person”


Centre of gravity for a person whose hands a stretched in the air

= Centre of gravity


Centre of gravity outside of a persons body

= Centre of gravity

Line of gravity Line of gravity - - The line of gravity is important The line of gravity is important when determining the stability of an object.when determining the stability of an object.

Line of gravity is the vertical line that passes through the centre of gravity to the ground.

If the line of gravity falls within the object’s base of support (i.e. its contact with the ground), the object is relatively stable.

If the line of gravity falls outside the object’s base of support (i.e. its contact with the ground), the object is relatively unstable.

Line of gravityLine of gravity

Centre of gravity

STABLE

Centre of gravity

UNSTABLE

Line of gravity Line of gravity

Base of support – Base of support – The object on the left is The object on the left is more stable because of its relatively larger BOSmore stable because of its relatively larger BOS

BOS is the area within an objects point of contact with the ground. The larger the area the base of support covers, the more stable an object will be.

Wide BOSNarrow BOS

BOSBOS

Line of gravity, BOS in relation to movementLine of gravity, BOS in relation to movement

The line of gravity (LOG) must go outside the base of support to initiate or continue movement.

The direction that the line of gravity takes relative to the BOS will be the direction of the resulting movement.

The further away the LOG is from the BOS, the greater the tendency the body has to move in that direction. E.g. Evasive running.

Line of gravity

Leg pushes against the ground

Top of body moves towards LOG

Direction of movement

Base of support

Centre of gravity, Line of gravity, Base Centre of gravity, Line of gravity, Base of support and Physical activityof support and Physical activity

Apply your knowledge!- Label the following images with the COG, LOG and BOS.- Is the performer stable?

5 Quick Questions5 Quick Questions

1. Name 3 ways to ensure you are stable (use biomechanical terms)

2. In relation to stability, what is one advantage of being shorter? (use biomechanical terms)

3. When you do a right handed lay up, what movement is occurring at your right hip?

4. What is the agonist muscle causing this movement?

5. What is the antagonist muscle during this movement?

ForceForce

What is a force?◦A push, pull or twist that causes movement of

an object

◦Force = Mass x Acceleration

◦Levers are used to apply a force

Levers – are used to apply forceLevers – are used to apply force

Consist of a pivot point (fulcrum) and a lever arm (connecting the pivot point to the resistance).

Lever arm

Resistance

Fulcrum (pivot point)

Downward Pressure

LeversLevers

The amount of leverage a person processes is dependent on the length of their body, in particular the length of their arms and legs.

Longer levers result in greater speed at the end of the lever arms – this is beneficial for throwing and striking objects.

Short levers can be moved with less force and at greater speeds – this is beneficial for moving body parts quickly and applying strength for pushing, pulling and lifting objects.

Question: From this information, what can you assume about a shorter person in comparison to a taller person?

Using Levers in SportUsing Levers in Sport

In the human body, levers are made up of the joints (fulcrum) and the bones that connect them to the objects being moved.

Levers in the human body can be manipulated to improve speed and apply large forces at the same time

Example: Running – lifting your foot and knee up will create a shorter lever, therefore you can run faster

Newton’s LawsNewton’s Laws

When exploring the area of biomechanics and human movement, it is useful to look at motion through the observations made by Sir Isaac Newton.

Newton was a famous seventeenth-century scientist who developed the three laws that govern all motion.

Newton’s 1Newton’s 1stst Law – The law of Law – The law of inertia.inertia.

‘A body continues in its state of rest or uniform motion unless an unbalanced force acts upon it.’

In other words, a body will remain at rest or in motion unless acted upon by a force. In order to get a body moving, a force must overcome the body’s tendency to remain at rest or inertia. The amount of inertia a body has depends on its mass.

Newton’s 1Newton’s 1stst Law – The law of inertia Law – The law of inertia

This soccer ball will remain at rest, until a force acts on it

Newton’s 2Newton’s 2ndnd Law – Mass, force & acceleration Law – Mass, force & acceleration

‘The acceleration of an object is directly proportional to the force causing it, is in the same direction as the force, and is inversely proportional to the mass of the object’.

When a force is applied to an object it will move in the direction the force was applied, and, depending on the size of the force and the size of the object, the object will accelerate accordingly.

A smaller object will move faster than a larger object. A greater force will move an object faster than a smaller force.

Newton’s 2Newton’s 2ndnd Law – mass, force & acceleration Law – mass, force & acceleration

Classroom experiment

Using the equipment you have been given, answer the questions in the workbook as a group

Newton’s 3Newton’s 3rdrd Law – action & reaction Law – action & reaction

‘Whenever a force is applied there is an equal and opposite reaction.’

If an athlete exerts a force onto the ground in order to push off, the ground will exert an equal and opposite force on the athlete, pushing them up into the air.

The first force of the athlete pushing into the ground is called an action force. The second force is called the reaction force (when the second body applies an opposing force back).

Newton’s 3Newton’s 3rdrd Law – action & reaction Law – action & reaction

Force summationForce summation

To give an object momentum in activities such as throwing, kicking or striking an object, the amount of momentum given to the object is determined by ‘the sum of all forces generated by each body part’ (i.e. Force summation).

To gain maximum momentum, the force needs to be generated by:

1. Using as many segments of the body as possible.2. In the correct sequence, using large muscles first

and then the smallest muscles last but fastest.3. With correct timing.4. Through the greatest range of motion.

Application of force summation – free-throw Application of force summation – free-throw shot techniqueshot technique

In order to maximise power and efficiency of the shot, the whole body is used.

Your body does not move all at once.

The shot begins with the movement of the legs, pushing into the ground.

The force is then returned back up the legs, up to the shoulders, down the forearms right to the release of the ball at the fingertips.

Application of force summation – free-throw Application of force summation – free-throw shot techniqueshot technique

Projectile motionProjectile motion

As soon as an object is thrown it becomes a projectile.

A projectile is influenced by the principles that govern projectile motion – gravity, air resistance, speed height, and angle of release.

Speed, height & angle of releaseSpeed, height & angle of release

Different angles of release affect the distance travelled and the height attained by an object.

When a ball is released from ground level, the optimal angle for release for maximum distance is about 45 degrees

The height of release is important when propelling an object anywhere higher than ground level. If an object needs to clear something higher than ground level (e.g. The cross bar on a goal post), the angle needs to be greater then 45 degrees.

90 degrees

0 degrees

45 degrees

Angle of release

Height of releaseHeight of release

The height an object is released with determine the distance the object travels

e.g.

Education

Year 11 biomechanics with levers, force summation