Biomechanics Yr 12 Session 2

Recalling the terms and laws relating to the motion of objects and efficiency of movement.

What is force?

A pushing or pulling influence that changes the state of an object’s motion.

Forces always have a

* A point of application
* Magnitude
* Direction

Ground reaction force is a force…

that acts on the body as a result of the body hitting the ground.

Eccentric force…

is a force that is **not applied through/to an object’s COG**, causing movement **and rotation.**

Recall that kinetics is the study of…

forces.

Kinematics is the study of…

motion.

What generally opposes motion?

Friction

Give two examples of quantitative analyses for movements in biomechanics

Timing 100m sprint

Measuring distance of long jump

Give two examples of qualitative analyses for movements in biomechanics

“Raise your core” (when doing the plank).

Keep your back straight (whilst squatting).

What category of analysis creates a digital image of the movement by cameras and other reflective mediums?

Optoelectronic motion analysis –

What category of analysis measures joint angles and the involving angles of objects upon movement?

Goniometry

What measures acceleration and speed of the body?

Accelerometers and light gates

\

What’s embedded in the ground to measure force output?

Force platforms

What records the electrical activity within the muscle just prior to contraction

Electromyography (EMG)

The Magnus Effect…

* Occurs when an object spins and moves through the air (eccentric forces acting upon the ball)
* This causes a pressure differential between the ball’s opposing sides (air moving faster on one side than the other \[high vs low pressure\],
* causing it to move on a curved path rather than a straight one.
* It will curve in the direction of the lower-pressure side. (Low pressure left, ball moves left).

Impulse is…

the time taken for applied force

Impact is when

two objects come into contact with each other in which there is an exchange of forces

Total momentum upon impact = The amount of momentum after impact

Energy in = energy out (no force lost)

Linear motion has an object…

move in a straight line (swimmer pushing off wall, downhill skier)

Curvilinear motion is

evident when a motion travels in a curved line (400m sprint)

Angular motion is motion that…

* happens when an object rotates around a fixed point/axis.
* e.g swinging a bat, golf swing

An axis or rotation can be…

* real or imaginary
* is a fixed point by which objects can rotate around
* can be linear (upon spinning while standing)
* horizontal (doing a backflip)
* and medial (cartwheeling)

General motion occurs when

* linear and angular motion is present
* e.g. 100m sprint (body in linear motion, angular motion of the joints)

Newton’s First Law of Motion

An object will remain at rest or continue in motion unless acted upon by a compelling force (intertia)

Newton’s Second Law of Motion

F = ma

for which

* more force = more mass and acceleration
* Note that increased mass = decreased acceleration

Newton’s Third Law

For every action, there is an equal and opposite reaction

Equilibrium occurs for an object when

all acting forces are equal and balanced

Static equilibrium occurs when…

vertical and horizontal torque = 0

Dynamic equilibrium occurs when…

there is no change in V.

\
* Don’t forget that the units for acceleration is m/s^2

What is a projectile?

An object that travels in motion through the air

\

A projectile is only affected by

gravity and air resistance

For an object, the coefficient of restitution concerns

* its elasticity upon impact - how bouncy it is
* the higher the coefficient of restitution, the bouncier the object is
* COR increases when temperature increase

*Angle of release* is the angle…

* relating to the horizontal (between 0–90º relative to the ground)
* optimum release for distance is 45º because any higher will act under gravity for longer. Any lower will reach the ground faster than optimal.

A parabolic angle of release is between the angles of

0º–90º

e.g hitting or kicking a ball

The angle of release for a vertical trajectory concerns an angle of

90º

e.g vertical jump

An angle of release that takes on a horizontal trajectory is from what angle?

0º

e.g throwing the ball in baseball.

*Speed of release* is the…

speed of the projectile at the instant of release

The vertical measure of the speed of release tells us

the height reached and flight time.

The horizontal measure of the speed of release tell us

the distance covered.

*Height of release*

is the height above the point of landing. The distance between where the projectile was thrown to where it landed.

The height of release dictates the optimal release angle.

\
True or false: When the height of release is positive, the optimal angle of release increases.

FALSE!

When the height of release is positive, the optimal angle of release decreases.

Likewise, when the height of release is negative (released lower than the landing point) **the optimal angle increases.**

When the height of release is zero, however, the optimal angle is…

45º

Define the concept of rebound

* Rebound refers to the speed and force of an object after it contacts a surface

More elasticity of an object yields:

* the object returning to its original shape faster
* will rebound further

Distinguish accuracy from precision

* Accuracy is the ability to successfully direct an object towards an intended target
* Precision is **repeatability** and consistency-based to a target

How can we improve accuracy?

* Flattening the swing arc: increases the window for success by increasing the distance of chance that results in the desired outcome.
* Following through: reducing the risk of deceleration by applying force over a longer period of time (which also brings about more control of the object).

The body’s centre of gravity is

* the point in which the object’s weight is evenly distributed
* the area where gravity appears to act on the object in which it will remain balanced

\[Of levers\] FLE means 123, denoting that…

**F** is in the middle for first-class levers, **L** is in the middle for second-class levers, and **E** is in the middle for third-class levers.

FLE

123

e.g. first class-levers bare the force **(F)** in between the Load and Effort

1st class levers have a mechanical advantage \[MA\]…

equal to 1

2nd class levers have a MA…

more than 1

3rd class levers have a MA…

less than 1

MA > 1 means that for a lever…

less effort to move resistance

MA < 1 means that for a lever…

more effort to move resistance

* Range of motion increases
* Angular speed increases