Download Newtons Laws, Stability, Levers

Biomechanics
Is a study of forces and their effects
on the human body during
movement.
Newton’s Laws of Motion
• Sir Isaac Newton was a famous seventeenthcentury scientist who developed three laws to
explain the relationship between the forces
acting on a body and the motion of a body.
Law 1: The law of inertia
• An object at rest tends to remain at rest unless acted
upon by some external force.
• In order to get a body moving, a force must
overcome the object’s tendency to remain at rest or
inertia.
• The amount of inertia an object has depends on its
mass.
• http://www.youtube.com/watch?v=by-7kkAu2Pg
Law 2: Acceleration
• When a force acts upon a mass, the result is
acceleration of that mass.
• The object will move in the direction the force
was applied.
• Depending on the size of the force and the
size of the object, the object will accelerate
accordingly.
• Smaller object = faster
• Bigger object = slower
Law 3: Action Reaction
• For every action there is an equal and opposite
reaction.
• E.g. If an athlete exerts a force onto the ground in
order to push off (Action Force), the ground will exert
an equal and opposite force on the athlete (Reaction
Force), pushing them up in the air.
• The two forces always work in pairs
ACTION – REACTION
• A runner exerts a force against the ground.
This creates an equal and opposite reaction
force which moves the body over the ground.
•
FORCE SUMMATION
• The summation (sum) of forces that have
accumulated throughout the bodies muscles
during an action.
• Allows maximal force to be produced by the
muscles and then transferred into physical
movements
Force summation can be maximised
by:
• Using larger muscles first, smaller muscles last
• Ensuring that the athlete is balanced and
stable so therefore the athlete can generate a
maximum force.
• Correct order of muscles
• Timing of muscles
COG
Centre of Mass in the centre
line of body. Provides
person wCentre of Mass in
the centre line of body.
Provides person with high
level of balance
ith high level of balance
Centre of mass outside midline of
body provides person with less
balance. More likely to fall over.
Line of Gravity
• Line of gravity is the vertical line that passes
through the centre of gravity to the ground.
• The line of gravity is important when
determining stability:
• If the line of gravity falls within the
object/person’s base of support [area in
contact with the ground] the object is
relatively stable.
• If the line of gravity falls outside the
object/person’s base of support they are not
Base of Support
• Base of support is the area within
an object or person’s point of
contact with the ground.
• The larger / wider the base of
support = more stable
• Narrow base of support = less
stable
Stability
• Stability is vital for all movements. Improved
stability often allows skills to be executed
more effectively.
• Stability can be improved through increasing
abdominal strength. This improves body
control and speed as a person is able to move
their centre of gravity in a direction more
effectively.
Stability is improved through:
• Widening the base of
support
Stability is improved
through:
• Lowering the centre
of gravity
Stability is improved through:
• Keeping the line of gravity within the base of
support
LEVERS:
• Are simple machines which apply force and
speed more easily.
• Levers help to move loads at greater speeds
• Muscles and bones act together to form
levers. A lever is a rigid rod (usually a length of
bone) that turns about a pivot (usually a
joint). Levers can be used so that a small force
can move a much bigger force.
•
External levers vs internal levers
• EXTERNAL:
• External levers allow force and speed to be applied
from outside the body
• E.g. paddles or oars in boats, pole in pole-vaulting
Internal levers
• For human movement the most important
levers are internal, within the body
• These levers are made up of:
– bones act as lever arms (resistance)
– joints act as pivots (Fulcrum)
– muscles provide the effort
forces to move loads (effort)
SHORT TO LONG
Moves from short lever
to a long lever in
kicking
Short lever allows more
speed
Long lever allows more
force
SHORT TO LONG…
Maximising lever length to improve
performance
• Shortening the lever arm (by bending at the
joint) allows the lever arm to GENERATE force
• Once this has been achieved the lever arm can
be lengthened (straighten the joint) to
maximise speed and force applied.
Kicking a rugby ball
Back swing: Kicking leg
is bent, creating a short
lever to swing towards
the ball at speed
Forward swing: Kicking
leg straightens creating a
longer lever allowing the
ball to be kicked with
more force (and speed)