Post on 16-Oct-2019
transcript
MOTION AND NEWTON'S LAWS
Definition
Motion is a change of
position or place of object
or subject in relation to a
fixed point or a reference
point.
Body motion is produced
or started by some action
of muscular system.
Distance :
Is a scalar quantity (having magnitude only).
Displacement:
Is a vector quantity (having magnitude and
direction).
Velocity:
Is a displacement divided by the time.
Speed:
Is a distance divided by the time.
1. Linear or translatory
motion
It is a motion in which any given point of the body moves along a straight line or a curved line
:All parts of the body travels
Same Distance
Same direction
In the same time
Rectilinear Motion
Each point of the segment moves in straight lines with:
Same linear displacement
Same linear velocity
Curvilinear Motion
Each point of the segment moves in curved lines with:
Nearly same linear displacement
Same linear velocity
2. Angular or rotatory
motion
Angular motion of any segment is rotation of this segment around a central imaginary line oriented perpendicular to the plane of
rotation called an axis of rotation. (rotation around an axis)
2. Angular or rotatory
motion
In angular motion each point of the segment travels through:
Same angular displacement
Different linear displacement
Same angle
Same direction
In the same time
The linear displacement depends on the length of the segment.
For example: if a tall and short subjects take the same angle ofhip movement during walking.
3. General motion
It is a combination between linear and angular motion.
For example: During walking and when the diver fall linearly
downward.
• Sports exercises : cumulative angular
motion of the joints imparts linear motion
to a thrown object (ball, shot) or to an
object struck with an instrument (bat,
racket)
NEWTON'S LAWS
The laws of motion constitute the
fundamental principles of statics, kinetics,
and kinematics.
Newton's laws of motion have many
applications to physical education
activities and sports.
The law states that:
Every body remains at rest or in
uniform motion at a constant velocity
until any force acts upon it to cause
any change
FIRST NEWTON'S LAW
Law of Inertia
Inertia
Inertia is a resistance of the body to any thing that tries to change its state of rest or motion
Types of inertia
Moving inertiaResting inertia
Inertia is directly proportional to the mass
Inertia
• The greater an object’s mass, the greater its inertia.
– the greater the mass, the more force needed to
significantly change an object’s inertia.
• Examples
– Sprinter in starting blocks must apply
considerable force to overcome his resting
inertia.
– Runner on an indoor track must apply
considerable force to overcome moving inertia &
stop before hitting the wall.
– Thrown or struck balls require force to stop
them.
Force is required to change
inertia
Any activity carried out at a
steady pace in a consistent
direction will conserve
energy.
Any irregularly paced or
directed activity will be very
costly to energy reserves.
Ex. handball & basketball
are so much more fatiguing
than running in a regular
speed
Resting inertia
The inertia of the body during rest
Clinical application:
Hanging
The sudden movement of thebody while the head is fixedwill cause dislocation of theatlanto-axial jointaccompanied by tearing of thetranseverse ligament.
Moving inertia
The inertia of the body during motion
Clinical application:
Whip lash injury (cervical syndrome)
When the car stops suddenly the trunk
will be fixed by the belt but the head is
still moving forward with the same
velocity of the car by the effect of moving
inertia . This will lead to fracture
dislocation of the atlanto-axial joint, but
without tearing of the transeverse
ligament so the subject will be alive
Law of Acceleration
SECOND NEWTON'S LAW
The law states that:
Acceleration produced by a force acting on the
body is directly proportional to the magnitude of
the force and inversely proportional to the mass of
the body and the movement occurs in the same
direction of the applied force.
Acceleration -: the rate of change in velocity
Change of velocity=AccelerationTime
a α fm
Force (F) = Mass (m)× Acceleration (a)
To attain speed in moving the body, a strong
muscular force is generally necessary
A much greater force is required from the
muscles to accelerate a 230-pound man than
than to accelerate a 130-pound man to the same
running speed
A baseball may be accelerated faster than a shot
because of the difference in weight
The force required to run at half speed is less
than the force required to run at top speed
To impart speed to a ball or an object, the body
part holding the object must be rapidly
accelerated
Law of reaction
THIRD NEWTON'S LAW
The law states that:
For every action there is an equal and opposite
reaction equal in magnitude and opposite in
direction
Clinical application
1. During standing on a hard surface
2. During walking
3. During push up exercises