Transcript BASIC CONCEPTS OF BIOMECHANICS

1.
2.
Linear motion – straight or
curved line. Motion along a
line. All parts same speed /
direction.
Angular motion – circle or
part of a circle. Movement
around a fixed point or axis.
3. General motion – combination of
linear and angular motion
1.
Pure linear motion
2.
Pure angular motion
3.
General motion
You need to be able to explain why they are
each type of motion
A push or pull that alters or tends to
alter, the state of motion of a body
“A force is that which alters or tends to alter a
body’s state of rest or of uniform motion in a
straight line.”
If a body changes direction or speed, a force has been
applied
Can it move something that is still to
move?
 E.G.,

A.
Cause a body at rest to move
B.
Cause a moving body to change
direction, accelerate or decelerate
C.
Change an object’s shape.
Effect of force
Example:
A force can cause a body at
rest to move
F exerted by foot – moves the ball from rest
A force can cause a moving
body to change direction
F exerted by GK hands redirects the ball
A force can cause a moving
body to accelerate
More F into kick = greater acceleration of the ball
A force can cause a moving
body to decelerate
Wind resistance decelerates the ball
GK hands decelerates the ball
A force can cause a body to
change its shape
Ball out of shape on kick / foot contact
Effect of force
Example:
A force can cause a
body at rest to
move
F by leg muscles to move the ‘returner’ into position
A force can cause a
moving body to
change direction
Force of racket (body muscles) will be exerted onto ball and send
ball in new direction (direction on the F applied)
A force can cause a
moving body to
accelerate
Greater muscular F exerted via racket to ball = greater acceleration
of ball to server (lighter ball = greater acceleration too).
A force can cause a
moving body to
decelerate
A force can cause a
body to change its
shape
Wind in opposing direction decelerates ball.
Resistance, so decelerates ball (gives more time before contact)
Time in air = greater gravitational deceleration
Racket contact with ball – ball warped (and racket)
Effect of force
Example:
A force can cause a body at rest
to move
Unless net (unbalanced) F acts, sprinters will stay in blocks
– still
A force can cause a moving
body to change direction
F from muscles and arms, pushes on blocks (N3L) and
pushes sprinter to change direction out of blocks.
A force can cause a moving
body to accelerate
Greater F – Quicker start time out of blocks and
acceleration down track
A force can cause a moving
body to decelerate
Greater wind resistance decelerates the sprinter
A force can cause a body to
change its shape
Air resistance – sprinters cheeks!
Drive from blocks – footwear and foot flatten / expand
with F application

Size of the force

Direction of the force

Without forces being
applied, there will be
no change in motion!

Whether still of
moving.

Sir Isaac Newton
3
Laws of Motion :
1 INERTIA
2 ACCELERATION
3 ACTION & REACTION

This is the law of inertia, and
states:

‘Everybody at rest, or moving
with constant velocity in a
straight line, will continue in that
state unless acted upon by an
external force exerted upon it’

Objects tend to remain either at
rest or in straight line motion.

In simple terms, to change the
motion of an object or
performer a force must be
applied.

A golf ball will only move from
the tee when a force is applied
to it from the golf club

A sprinter will only move out of
the blocks when they exert
force from their muscles

This is the law of acceleration, and states:

‘The acceleration of a body is proportional to the force
causing it and the acceleration takes place in the direction
in which the force acts’

This law describes the relationship between net force,
acceleration, and mass

Often described as:
F = ma Force = mass x acceleration
 This law suggests that the greater
the mass of an object, the greater
the force required to give the same
amount of acceleration and also
the greater the force applied the
greater the acceleration

For example, less force is applied
to the shuttlecock than to a shot
put in order for it to move

F - ma

At a constant velocity
the force of tire
friction (F1) and the
force of air resistance
(F2) have a vector
sum that equals the
force applied by the
cyclist (Fa).

The net force is
therefore 0.

More mass results in less
acceleration when the
same force is applied.

With the same force
applied, the riders and
the bike with twice as
much mass will have half
the acceleration, with all
other factors constant.

Note that the second
rider is not pedaling.

One person is to
use the bats and
balls to devise a
sporting example
to explain how
mass and
acceleration
affect each other.

Those taking part
can only agree or
disagree.

If you do disagree
you take over as
the teacher.

Are you able to do
the same for the
third Law?

Those taking part
can only agree or
disagree.

If you do disagree
you take over as
the teacher.

This is the law of reaction, and
states:

‘To every action there is an
equal and opposite reaction’

When a swimmer for example
exerts a force on the starting
blocks, the blocks exert an
equal and opposite reaction
force upon the swimmer,
propelling them into the pool

The American football
player's foot is pushing
against the ground, but it is
the ground pushing against
the foot that accelerates
the player forward to
catch a pass.
1st Law – INERTIA - remains at set unless a
force affects them
2nd Law – ACCELERATION - push harder to
get more acceleration
3rd Law – ACTION & REACTION - action
force is muscular force, reaction force pushes
athlete off blocks

Draw a free flow diagram
using Newton's laws of motion
to describe the resultant forces
 If you agree
impacting on the ball.
with what is
being
drawn then
allow them
to continue.

If you
disagree
then you
take over.
 The amount of material of
which it is made.
 Shot put vs foam ball
 Used to advantage in sports?

The point at which the body is balanced
in all directions

Distribution of mass – symmetrical

Body position and shape –
unsymmetrical; males vs females

Changing positions – HJ (Western Roll vs
Fosbury Flop

With a partner one of you stand with your back
against a wall. Your heels against the wall

Try and place a ball down on the floor without
moving your feet.

See if your partner can place the ball further
away?
Why do you fall
forwards?
 Or if you don’t fall
why do you feel like
falling?


Distribution of weight around a
balance point

The centre of a body's mass. In the
human body it is the point, which all
parts are in balance with one another.

It is dependant on current position in
space, anatomical structure, gender.
 Relates
to how difficult it is to
disturb a body from a balanced
position

Is determined by :

Position of athlete’s centre of mass

Position of the athlete’s line of gravity=
a line extending from the centre of
mass vertically down to the ground.

Size of the athlete’s area of support
Adopt a wide stance arms down
 Adopt a wide stance arms up
 Feet together arms down
 Feet together arms up


Is there a difference in how easy it was to
move the person?

We talked about angular and linear
motion at the beginning of the class, so
how can we create these types of
motions?

Investigate how you can cause these
actions using the tennis ball.
 Think about the force that you are
applying and the centre of mass.


Linear motion – force
passes through the centre
of mass DIRECT FORCE

Angular motion – force
passes outside the centre of
mass ECCENTRIC FORCE
Application of
F
Type of F
Type of M
F passes
through the
C of M
DIRECT
LINEAR
F passes
outside the
C of M
Movement in
circle (part)
around axis
of rotation
ECCENTRIC
ANGULAR
Egs of this
•Tennis drive
•Vertical jump
•Shot put
•Tennis topspin or
slice
•Curve ball / spin
•Beckham free
kick
•Golf wedge shot
Throw a tennis ball into the air making it
spin.
 Draw a diagram that shows the centre of
mass, the point of application of Force
Action/Reaction
 Direction of force.
 What is the scientific name given to the
force resulting in the angular motion.


Using the bat and ball in your groups can
you cause the ball to move in a linear
motion by applying a direct force?

Can you apply an eccentric force to
cause the body to move with an angular
motion.

What would be a really good sporting
example?
Draw a free flow diagram of a sprinter in
the blocks.
 Explain the Laws of motion, mass, and
force.
