Transcript File

Biomechanics
Introduction
Planes of
motion
&
Axes of
rotation
LEVERS
 The
function of a lever in the body is either:
 To
overcome a force greater than the effort used eg a
crowbar / a calf raise
 To move something a greater distance eg an overarm
throw
A
lever consists of:
A fulcrum or pivot point – a joint
 Load – could be gravity, body weight,
added weight e.g. gym equipment
 Effort – provided by muscular
contractions

THE LEVERS IN THE BODY ARE THE
BONES OF THE SKELETON –
LEVERS CAN BE ADDED IN THE FORM OF
SPORTING IMPLEMENTS
RACKETS
CLUBS
BATS
Sporting levers
•Golf clubs are selected according to
length – a longer club will produce a longer
lever and will send the ball further
•A defender in hockey will use a heavier
stick
•An overarm serves in tennis makes the
most use of the power by making the lever
as long as possible
•A cricketer hitting for 6 will play the shot
to make the most of a long lever produced
by his body, arms and the bat.
LEVERS
REMEMBER- FLE
The part of the lever
that is located in the
middle
First Order Lever
 The
fulcrum is in the middle
 The load is at one end and the
effort applied at the other
 Example
in the body =
Joint at the neck
Second Order Lever
 The
Load is in the middle
 The fulcrum is at one end, the
effort applied at the other
 Example
in the body =
The ankle joint
Third Order Lever
 The
effort is in the middle
 The load is at one end, the fulcrum at the
other
 Example
in the body =
most of our skeletal
muscles
FORCES

Before looking at sport & movement, we must understand
FORCE
A force is a push or pull that alters or tends to alter the state of
motion of a body


A Force can cause a body at rest to move – (taking a football
penalty- the force applied with the foot make the ball move)
A force can cause a moving body to:

Change direction – (returning a tennis shot)

Accelerate – (a sprint finish)

Decelerate – slowing down at the bottom of the ski slope)

Change an object’s shape – (jumping on a trampoline)
 If
a force is applied through the middle of an
object – it causes LINEAR MOTION
 If
a force is applied off-centre it will cause spin or
ANGULAR MOTION
Many sporting examples are a
combination of both angular and linear
motion:
•The upper body shows
“LINEAR MOTION”
•Whilst the legs show
“ANGULAR MOTION”
This combination is called “GENERAL MOTION”
•Internal forces are generally produced by
concentric muscle contraction
•External forces could be:
•Gravity
•Air resistance (water resistance)
•Friction
•Reaction
NEWTON’S LAWS OF MOTION
NEWTON’S FIRST LAW
“A body continues in a state of rest or of
uniform velocity unless acted upon by an
external force” Law of inertia
NEWTON’S SECOND LAW
“When a force acts on an object, the rate of change
of momentum experienced by the object is
proportional to the size of the force and takes
place in the direction in which the force acts” –
Law of acceleration
NEWTON’S THIRD LAW
“For every action there is an equal and
opposite reaction” - reaction
Consider:
An ice hockey puck is hit by a player & travels across the
ice to rebound from the far wall of the rink.
Assume that the friction between the puck & the ice & the air
resistance are negligible, & that the puck travels from R to L
Use Newton’s Laws of motion to explain
what is happening in the following
situations:
1.
While the puck is stationary before
being hit
2. While the stick is in contact with the
puck
3. While the puck is travelling across
the ice before it hits the wall
4. While the puck is in contact with the
wall
TASK:
Write a short piece to apply what you know from
today’s lesson to your selected sport
Can you explain how forces are functioning to:
•Cause something to move
•Change direction
•Accelerate
•Decelerate
•Change the shape of an object
Selected sport: trampolining
•Forces acting - pull of gravity makes the performer
return to the trampoline – force of the performers
muscles changes the shape of the trampoline bed –
the force of the trampoline against the performer
will cause them to change direction
•Application of Newton’s Laws - External force of
performers muscles causes movement (1st Law of
acceleration) – The greater the distortion of the bed,
the greater the force acting to push the performer
upward – they will therefore go higher (2nd Law of
acceleration) – The action of landing on the bed
causes the reaction of sending the performer upward
(3rd Law of reaction)
Centre of Gravity / Centre of Mass
“The point at which the
body is balanced in all
directions”
Centre of Gravity & stability
 The
lower the centre of gravity is – the more
stable the position
Base of support
 The
larger the base of support – the more stable
the position
Line of Gravity
 An
imaginary line straight down from the
centre of gravity / mass
•If the line of gravity is at the centre
of the base of support – the position is
more stable
•If the line of gravity is near the edge
of the base of support – the position is
less stable
•If the line of gravity is outside the
base of support – the position is
unstable
To work out the centre of gravity of a 2D
shape Hang
the shape from one point & drop a
weighted string from any point on the object
 Mark the line where the string drops
 Repeat this by hanging the object from
another point
 Mark the line again where the string drops
 The centre of gravity is where the two lines
cross
Jessica Ennis – London 2012