Download Biomechanics explains the way we move our bodies. It is a science

Biomechanics explains the way we move our bodies. It is a science that examines
the internal and external forces acting on the human body, and the effects of those
forces.
Applications:
-
why does a golfer slice the golf ball?
Why have pole-vaulters increased their heights since the use of fiberglass
poles?
How are prosthesis designed for amputees?
How do divers analyze their form and affect corrections
How do cyclist helmets affect their speed?
Why does a knuckle ball move in the air?
How can the Laws of Physics help us understand the Discus?
The most high profile biomechanical conundrum in recent times has been the
inclusion of Oscar Pretorius in the Summer Olympic Games of 2012. The “Blade
Runner”, a double leg amputee, uses artificial prosthesis in the form of two metal
blades to run with. Does this give him a biomechanical advantage? At what phase of
the race does he have an advantage vs. a disadvantage?
To answer these we need to understand many Biomechanical concepts. Examples
are given – but also think of other examples in sports and exercise.
Force is a power acting on a object. The sum of all forces is called a NET FORCE.
Eg. Gravity is a force that acts in a downward fashion towards the earth’s
core. Muscular thrust on the ground can enable a high jumper to clear a bar.
Forces can be represented by:
- a Scalar Quantity (60 miles per hour) or
- a Vector Quantity which includes both Magnitude AND Direction
o A Vector is represented by an arrow – the longer the vector, the
more powerful the force
Speed is a motor ability to move the body, or body parts, in the shortest amount of
time
Velocity is a measure of distance traveled per unit of time…eg. Usain Bolt has
reached peak velocities of over 12 Meters a second and average velocities of over 10
Meters a second over a 100 meter race.
Mass is the measure of how much matter a body has. It is different from Weight,
which is assigned a numerical value representing the force exerted by gravity of that
body to the ground. Therefore, on earth, a man may measure 200 lbs, but will
weigh nothing in space. However, he would have the same Mass on earth as in
space.
Gravity, in a sporting example, is a measure of the force of attraction between the
athlete and the earth, which can vary in magnitude according to where you are on
the earth. In the 1968 Olympics, Bob Beamon jumped 29 feet 2.75 inches (approx
8.9 meters) in the thin air of Mexico City (7,349 feet above sea level). This world
record held for over two decades. The farther the athlete is away from the center of
the earth (equator, mountains) the less the Gravity or force of attraction.
Center of Mass, or Center of Gravity is the point around which the body’s mass is
equally distributed. The Center of Mass of an object that is perfectly symmetrical
and with common density, such as a bowling ball, would be at its geometric center.
Your Center of Mass is not always found within you body, but is usually found 6
inches above the groin area.
Displacement is the Length and Direction an athlete or Object travels from start to
finish during a performance (eg., a Volleyball player jumps 0.8 meters during a
block attempt)
Acceleration is the RATE of change of VELOCITY. Increasing speed and decreasing
speed is key to a sports performer’s success. Can a soccer player accelerate past a
defender from a standing start? Or can they also decrease their velocity at a higher
rate than the defender?
Momentum is the PRODUCT of the body’s Mass and its Velocity. It is the amount of
motion gained or lost by the body.
Impulse creates momentum, but momentum is lost by Impact.
Eg. A basketball Player draws a defender into a screen. The defender gains
momentum through the impulse of his legs generating force on the court, but
the momentum is lost when he or she impacts the screen player.
Give at least one example of each of these Biomechanical Concepts.
The Mechanics of Levers:
There are three aspects to Levers –
A LEVER is a rigid body (long bone) that rotates around a fixed point
called an AXIS (joint) or FULCRUM. FORCES, Resistive (weight of
limb) and Applied (muscle contraction) act on the lever.
There are three classes of Levers:
First Class (eg.- Neck Extension – also a Teeter Totter)
Second Class (eg. Toe Press)
Third Class (eg. snow shoveling)
Referring to the Diagrams, and using stick figure models, give two examples in
sports of each of these different level classes in action. In each diagram show the
Fulcrum, the Effort (muscular resistance) and the Load.
Newton’s Laws of Motion:
According to Newton's first law...
An object at rest will remain at rest unless acted on by an
unbalanced force. An object in motion continues in motion with
the same speed and in the same direction unless acted upon by
an unbalanced force.
This law is often called
"the law of inertia".
What does this mean?
This means that there is a natural tendency of objects to
keep on doing what they're doing. All objects resist changes
in their state of motion. In the absence of an unbalanced
force, an object in motion will maintain this state of motion.
According to Newton's second law...
Acceleration is produced when a force acts on a mass. The
greater the mass (of the object being accelerated) the greater the
amount of force needed (to accelerate the object).
What does this mean?
Everyone unconsciously knows the Second Law. Everyone knows
that heavier objects require more force to move the same
distance as lighter objects.
However, the Second Law gives us an exact relationship
between force, mass, and acceleration. It can be expressed
as a mathematical equation:
or
FORCE = MASS times ACCELERATION
According to Newton's third law...
For every action there is an equal and opposite re-action.
What does this mean?
This means that for every force there is a reaction force
that is equal in size, but opposite in direction. That is to say
that whenever an object pushes another object it gets pushed
back in the opposite direction equally hard.
Refer to Video Clips illustrating Newtons Laws. Can you come up with
your own examples in Sports?
Projectile Motion:
Any airborne object, including the human body, is a projectile. The center of mass of the
projectile will follow a Parabolic Path whenever gravity is the only external force acting
on it. Skills involving projectiles might have one of three objectives. In the high jump,
the objective is to maximize the Height over the bar; in the Javelin the thrower tries to
maximize the horizontal distance or Range; and in basketball the shooter seek Accuracy.
-
to maximize the vertical distance (height) of a projectile, one must maximize
the takeoff velocity and takeoff verticality. High jumpers try to jump as
vertical as possible with as much speed as possible built up.
To maximize the horizontal distance (range) of a projectile, one must achieve
maximal takeoff velocity and take off at an angle of 45 degrees to the
horizontal. Most throwing events in the Olympics (Javelin, discus, shot,
hammer) try to achieve a takeoff angle of 45 degrees, as well as baseball
players throwing in a baseball from the outfield.
Fluid Dynamics:
A Fluid is a substance that flows – such as liquid OR gas. Air is a fluid. All athletic
events are affected by fluids – some more than others. Walking, dancing or gymnastics
are not affected that much. Cycling, swimming, surfing, and skiing are directly affected
and baseball, cricket, and soccer involve projectiles that are definitely affected by fluid
dynamics.
Fluid Drag Forces:
- Profile Drag is the resistance caused by the size of the object or person and
the Air Turbulance that is produced as it moves through the air.
How is this apparent in Skiing, cycling and running?
- Skin Friction Drag, or Surface Drag is caused by the surface roughness of
the object or person.
If an object is smooth, it will incur less skin friction or drag. The high tech swim
suits in Olympic swimmers re designed to incur the least surface drag possible.
The bowler in Cricket only shines one side of the ball so that it has more drag on
the other side and will “move” in the air.
Fluid Lift Forces: a forces directed perpendicular to the flow direction of the
moving object. These forces can be directed upward (as in discus, javelin, ski
jumping, Frisbee ) or downward ( as in Racing Cars, sinker balls in baseball,
topspin shots in tennis) or even sideways ( as in curveballs or in the Beckham free
kicks).
- the TILT of the object relative to the flow velocity is the Angle of Attack.
For example is a discus is lifted slightly upward it will create a lift force that will
make it go further than a discus that is flying directly level with the vector of
forward movement.
The Berrnoulli Princple:
When a fluid hits an object of uneven shape – like an aircraft wing – the air on the
curved side will have to travel faster than the air on the straight side. Bernoulli’s
principle sates that the higher the velocity of the fluid, the lower the air pressure.
The slower the velocity, the higher the air pressure. This creates a lift force
Upwards which is responsible for aircraft being able to fly.
The opposite is true for the Tail Airfoils of racing cars which are flat on top and
curved beneath to create a downward force.
The Magnus Effect:
This concept applies to spinning objects in motion. It only applies to
objects spinning around an axis NOT aligned to the flow velocity. So a
quarterback throwing a football with a tight spiral is not subject to Magnus force.
However a topspin forehand in Ping Pong brings the ball down in an exaggerated
fashion. Topspin restricts the horizontal distance and time in the air, whilst
backspin increases the distance and time in the air. For example the golfer will
increase the height, the time in the air and enhance the ability of a golf ball to stay
on the green due the angle of decent being greater.
http://www.youtube.com/watch?v=23f1jvGUWJs
Try to find examples of each of these biomechanical concepts have affected sports
over the years.
- for example, how has the modern tennis racket enabled the tennis player to be
more effective, that when they were using wooden tennis rackets?
Projectile Experiment:
Design a Practical Experiment to examine the role of speed and angle in the
distance a projectile travels.
Football punting/leg speed, whiffle ball throw, baseball machine and angles of
release/distance, Basketball shot and angles/success, soccer kick/bending
freekicks