Download MECHANICS, MOTION AND MOVEMENT

MECHANICS, MOTION AND MOVEMENT
Motion
LINEAR MOTION
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When a body moves in a straight or curved
line, with all its parts moving the same
distance, in the same direction and at the
same speed. E.g. Linear motion in a
straight line = Tobogganist. Linear motion
in a curved line = shot in shot put
ANGULAR MOTION
-
GENERAL MOTION
-
When a body or part of a body moves in a
circle or part of a circle about a particular
point called the axis of rotation. The
movement must occur around a fixed
point/axis. E.g. when an athlete spins, turns,
circles or somersaults. The fixed point in the
human body is usually joints. Angular
Motion of a body part = the arm
when swimming front crawl – shoulder acts
as the fixed point. Angular Motion of the
whole body = when a Gymnast swings
around the high bar
A combination of Linear and Angular
Motion. E.g. Javelin – the approach shows
Linear Motion with the Javelin and torso of
the athlete; while showing Angular Motion
through the movement of the legs and nonthrowing arm
Force
This is ‘a push or a pull that alters, or tends to alter, the state of motion
of a body.’
A force can perform the following functions:
 Cause a body at rest to move
 Cause a moving body to:
o Change direction
o Accelerate
o Decelerate
 Change an objects shape
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The effects of force on a penalty kick in Football are given in the table below:
EFFECT OF FORCE
EXAMPLE FROM A PENALTY KICK
IN FOOTBALL
The Football will remain at rest on the
penalty spot until the force of the
footballer’s boot on the ball causes it
to move
If the ball is travelling towards the
goal and the goalkeeper makes a
save, the force exerted by the hands
of the goalkeeper will push the ball
away in the opposite direction
The penalty taker can accelerate
faster towards the ball, after initially
starting to move, by applying a larger
force on the ground
The force of the net at the back of the
goal will cause the ball to slow down.
Or the force of the goalkeepers hands
on the ball will cause it to stop moving
At the point where the player’s boot
contacts the ball, the ball will be
slightly deformed and no longer truly
spherical. The force of the ball on the
net will also cause the net to change
shape
A force can cause a body at rest to
move
A force can cause a moving body to
change direction
A force can cause a moving body to
accelerate
A force can cause a moving body to
decelerate
A force can cause a body to change
its shape
YOU WILL NEED TO BE ABLE TO EXPLAIN THE FOLLOWING WHEN
RELATING TO SPORTING EXAMPLES:
 The Effect of Size of Force
 Direction of the Force
 Position of Application of Force on a Body
Link between Force and Motion
‘Without Force, there can be no Motion’
Newton’s Laws of Motion
1ST LAW OF MOTION
(‘Law of Inertia’)
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‘A body continues in a state of rest or
of uniform velocity unless acted upon by
an external force’
E.g. Hockey ball during the penalty flick. ‘A body (the Hockey ball) continues
in a state of rest (on the penalty spot) unless acted upon by an external
force (the muscular forces on the Hockey stick).’
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2ND LAW OF MOTION
(‘Law of Acceleration’)
‘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’
E.g. Hockey ball during a penalty flick ‘When a force acts on an object (the
muscular forces applied to the stick on the ball), the rate of change of
momentum experienced by the object (the acceleration of the Hockey ball)
is proportional to the size of the force (the ball will accelerate faster with a
greater push of the stick) and takes place in the direction in which the force
acts (the ball accelerates towards the Hockey goal).’
-
3RD LAW OF MOTION
(‘Law of Action/Reaction’)
‘For every action there is an equal and
opposite reaction’
E.g. a Rugby player swerving to the right to avoid a tackle ‘For every action
(the Rugby player pushes the ground to their left with their feet) there is
an equal and opposite reaction (the ground exerts an equal force to the
right allowing the player to swerve in that direction).’
Centre of Mass (CoM)
CENTRE OF MASS
-
‘The point at which the body is balanced
in all directions.’ Also the point at where
all of its mass could be considered to be
concentrated
MASS
-
The amount of material of which a body
is made
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With symmetrical objects in which the mass is evenly distributed, the
centre of mass is found at the geometrical centre of that object e.g.
shot put
Sometimes the CoM can lie outside the body. E.g. the CoM of a ring
will be at the centre – outside the object itself
In humans the CoM is not a fixed point; as it depends on the position of
the body and can also lie outside of the body
CoM of a male standing upright with their arms to the sides is about 23cm above the naval and slightly lower for a female (as males tend to
have more weight in their shoulders and women tend to have more
weight on their hips)
As soon as an athlete moves from that position, so does the CoM. E.g.
if the arms are raised above the head then the CoM will raise as well
In other body shapes the CoM can move outside the body. E.g. Pike
Jump in Gymnastics or Trampolining (CoM will be outside the stomach
as the arms and legs move forwards) or the Fosbury Flop in High Jump
(CoM comes out the back of the body as it bends backwards)
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Stability
‘Relates to how difficult it is to disturb a body from a balanced position’
This is determined by a number of mechanical principles that depend on the
following:
 Position of athlete’s CoM
 Athlete’s base of support (e.g. feet)
 Mass of the athlete
 Position of the athlete’s line of gravity (a line extending from the CoM
vertically down to the ground)
PRACTICAL EXAMPLES OF THE EFFECTS OF CHANGES IN THE
POSITION OF THE CoM AND THE AREA OF SUPPORT
YOU NEED TO BE ABLE TO APPLY THIS TO PRACTICAL EXAMPLES
FROM VARIOUS SPORTS
Relationship between CoM and Application of Force
LINEAR MOTION
-
ANGULAR MOTION -
If the line of action of the force passes through the
body’s CoM, the resulting motion will be linear.
E.g. an athlete performing a vertical jump. A force
that passes through the CoM of a body is called a
Direct Force (a force whose line of application
passes through the CoM of a body causing the
resulting motion to be linear)
If the line of action of the force passes outside the
body’s CoM, the resulting motion will be angular.
E.g. forward somersault on the trampoline. A force
That passes outside the CoM of a body is called
Eccentric Force (a force whose line of application
passes outside the CoM of a body causing the
resulting motion to be angular)
PRACTICAL ANALYSIS OF TYPICAL PHYSICAL ACTIONS
YOU NEED TO BE ABLE TO COMPLETE A PRACTICAL ANALYSIS OF A
NUMBER OF PHYSICAL ACTIONS INCLUDING THE FOLLOWING:
 Kicking a Football
 Passing a Netball
 Long Jump
 Shot Putt
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EXAM QUESTIONS
JANUARY 2003
1
d)
Knowledge of force can be beneficial when analysing physical
activities.
Using practical examples explain how the size of force, direction
of the force and position of application of the force can affect
performance.
(3 marks)
MAY 2003
No Questions
JANUARY 2004
1
b)
With reference to the centre of mass, explain why a headstand
is an easier balance to hold than a handstand.
(3 marks)
MAY 2004
1
c)
During an analysis of practical activities, movement can be
described as linear, angular or general motion.
Use a practical example to describe how angular motion could
be produced.
(2 marks)
JANUARY 2005
No Questions
MAY 2005
1
b)
When hitting a ball in Tennis an understanding of force is
important. Explain how force can cause the ball to:
(i)
(ii)
Move straight
Spin
(2 marks)
JANUARY 2006
No Questions
MAY 2006
1
c)
Describe how the position of the centre of mass can affect a
balance.
(3 marks)
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JANUARY 2007
1
b)
Use a practical example to describe how angular motion is
produced.
(1 Mark)
MAY 2007
1
b)
iv)
Apply Newton’s 3 Laws of Motion to a strength training
exercise.
(3 Marks)
JANUARY 2008
1
c)
Explain, using a practical example, how either size or direction
of force can affect performance in PE and sport.
(2 Marks)
MAY 2008
1
b)
Movement can be described as linear, angular or general
motion.
(i)
Use a practical example to describe how linear motion
can be produced.
(2 Marks)
(ii)
A knowledge of centre of mass in physical education and
sport can improve performance.
Using a practical example from PE or sport, explain how
the position of centre of mass enables a performer to
resist motion or external forces.
(3 Marks)
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