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PE - Biomechanics
Today we’ll look at…
Newtons laws 1,2,3
Forces and what they can do?
Centre of mass and stability
Types of motion
Newton’s First Law of Motion
A body continues in a state of rest or uniform
velocity unless acted upon by an external
force.
Sporting Examples:
“ A football will stay on the penalty spot until kicked”
“A hockey ball will remain still until hit by the stick”
“ A football will roll until slowed by friction or
another player”
“ A hockey ball will not fall from the air without the
application of gravity”
Newton’s First Law of Motion
A body continues in a state of rest or uniform
velocity unless acted upon by an external
force.
Newton’s First Law of Motion
A body continues in a state of rest or uniform
velocity unless acted upon by an external
force.
PUSH or PULLS can alter a body (object) in the following ways
•Cause a body to move (as seen in the previous slide)
•Cause a body to accelerate
•Cause a body to decelerate
•Cause a body to change direction
•Cause a body to change shape
Forces Can Cause a body to accelerate
Sporting example:
Sailing boat.
The force that causes the boat to acceleration is the wind.
Forces Can Cause a body to decelerate
Sporting example:
Sailing boat.
The force that causes the boat to deceleration is the wind.
Forces Can Cause a body to change direction
Sporting example:
Tennis
The force that causes the Ball to
change direction is the racquet
impact.
Forces Can -
Ball shape is
compressed by the
force of the club head
on impact
Cause a body to change shape
Sporting example:
Golf
The force that causes the ball to change shape is the impact
from the club head.
Newton’s Second Law of Motion
When a force acts on an object, the motion
experienced by the object is proportional to
the size of the force and in the direction in
which it is applied.
Sporting Examples:
“If you kick a football hard, it will go a long way”
“If you kick a football softly it wont go very far”
“If you hit a hockey ball to the left, it will go left”
“If you hit a hockey ball to the right, it will go right”
Newton’s Third Law of Motion
For every action there is an equal and opposite
reaction.
Sporting Examples:
“If a rugby player pushes to the left with their foot,
they swerve to the right.”
“A high jumper needs to push down on the ground to
be able to go up.”
A football goalkeeper needs to push to the left with
their feet in order to dive to the right.”
Reaction force is the goal
keeper lifting into the air
in the opposite direction
Action force is the goal
keeper pushing down into the
floor
Centre of Mass
An imaginary
point
which is
movable
and is where
the
mass of an
object
is concentrated.
Centre
Of
Mass
As the mass of
the arms move
up so will the
centre of mass
Centre
Of
Mass
Stability
Stability is
dependant
on the
Centre of
Mass being
directly
above the
Base of
Support
Centre
Of
Mass
Base of
Support
Stability
Centre
Of
Mass
Stability is
dependant
on the
Centre of
Mass being
directly
above the
Base of
Support
Line of
Gravity
Base of
Support
STABLE
Stability
Stability is
dependant
on the
Centre of
Mass being
directly
above the
Base of
Support
UNSTABLE
Centre
Of
Mass
Line of
Gravity
Base of
Support
Centre of Mass
Remember Centre Of Mass doesn’t always need to be
inside the body
Stability is dependant on 4 things
Position of the
centre of mass?
Size of the base
of support?
Mass of the
Athlete?
Where the line of
gravity is?
Motion - Linear
When a body moves in a straight line with all
its parts moving the same DISTANCE,
DIRECTION, and SPEED
Everything is moving in the
same direction at the same
speed
SPORTING EXAMPLE = THE BOB SLEIGH
(TOBOGGAN)
Motion - Angular
When a body or part of a body moves in a
circle or part of a circle about a point (the
axis of rotation).
Circular motion about a point.
i.e. The elbow being fixed
when the forearm moves in a
half circle in a tennis serve
Axis of rotation
SPORTING EXAMPLE = BENDING YOUR ARM IN A
TENNIS SERVE
Motion – General
General = Angular +Linear
General motion is a combination of Linear and
Angular motion
Sporting examples
•Javelin
•Wheel chair athletics
•Swimming
•Running