BIOMACHANICS NOTES FOR GRADE 12
DEFINITION OF BIOMECHANICS
What is biomechanics in relation to physical education and sport?
 Biomechanics is the study of the movement of living things using the science of mechanics.
Biomechanics is the science that examines the external and internal factors acting on human body
and the effects produced by these forces. Biomechanics studies what makes a body move and the
results of that movement.
 DEFINATIONS USED WHEN DISCUSSING MOTION.
 MASS – is the amount of material which an object is made.
 WEIGHT- is the force of attraction between an object and the earth. Weight depends
very much on the mass of the body .( w = m x g )
 VELOCITY – is the rate at which a body moves from one location to another.
 ACCELERATION – is the rate at which velocity changes with respect to time.
 SPEED = distance covered
Time taken
FORCES AND BODY LEVERS
A force can be described as a push or pull or the effect that one body has upon another.
Force can; 1. Cause a body to move
2. Cause a moving body to slow down, stop, and increase its speed or change direction.
Forces can produce three types of movement either separately or together:
Deformative movement. A force that changes the shape of the body.
Translational movement: A force that moves the body from one place to another.
Rotational movement: A force that causes a body to rotate.
What happens when you kick a ball? When you kick a ball, you produce the three types of movement at
one time.
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1. Deformation. 2. Translation (forward movement) and Rotation (spin)
The magnitude of acceleration caused by a force will depend on the mass of body being moved. For a
given force, the larger the mass, the smaller the acceleration. (Which is why sprinters for example, aim
not to carry excess weight.)
MEASURING FORCE.
Force can be measured in terms of: magnitude, Direction, Point of application and line of action.
INERTIA AND FORCE.
What is inertia?
This is the property of matter that causes it to resist change. When you want to set a body in motion, you
need to overcome the tendency of the body to remain at rest.
What is force therefore? Force can also be that which alters or tends to alter a body’s state of rest in a
straight line.
Where do forces that act on a body come from?
1. Originate within the body
2. Originate outside the body.
 FORCES ORIGINATING WITHIN THE BODY
Forces originating within the body are provided by concentric and eccentric muscle contraction which
acts upon the bones with sufficient force to set them in motion. A muscle creates a pull by contracting
along its long dimension.
 FORCES ORIGINATING OUTSIDE THE BODY.
Gravity is the most persistent of the outside forces acting on the body. All objects within the earth
gravitational field are constantly acted upon by the force of gravity.
The magnitude of the gravitational attraction is called weight.
Centre of gravity is the point of concentration of mass. In human body the in standing position is
considered to be in the hips.
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 LAWS OF MOTION.
NEWTONS FIRST LAW OF MOTION .THE LAW OF INERTIA
Newton’s first law of states that; an object at rest tends to remain at rest unless acted upon by some
external force.
The law also expresses that an object in motion tends to remain in motion and to travel in a straight line
with uniform velocity unless acted upon by some external force.
There are two basic types of motion;
1. Linear motion –occurs when an object or person travels in straight line.
2. Angular motion –occurs when an object turns about the point of axis, fulcrum gymnastics skills
when an athlete twists or turns.
Example. a deflected ball in basketball pass . the applied force accelerates the ball in the direction which
the force acts .in order for the direction of the ball to be changed completely to the direction in which the
second force is applied , the second force must be much greater than the first.
Basically , if an object is motion , it keeps going unless something stops it .some examples of outside
force that affect inertia are gravity , the surface of playing field , a defensive player or the braking action
of an athlete’s body to stop. Because of every objects tendency to maintain its state of motion (inertia)it
takes more force to start an object moving than to keep it moving.
SECOND LAW – THE LAW OF ACCELEATION (LLAW OF MOMENTUM)
Newton’s second law of motion states that when a body is acted upon by a force its resulting change I
momentum ( acceleration )is proportional to the force causing it , and inversely proportional to the mass
and the change takes place in the direction in which the force is applied. The produced acceleration or
deceleration is proportional to and in the same direction of force. Example, a baseball player hits ball with
double the force, the rate at which the ball will accelerate (speed up) will be doubled. Football players can
slow down, stop or reverse the direction of the other players depending upon how much force they can
generate with direction.
MOMENTUM is the amount motion possessed by a moving object. Everybody in motion has certain
mass and a certain velocity, the product of these two is its momentum. Meaning the body’s momentum
can be changed by mass or its velocity.
 COLLUSION
Momentum is important when there is collusion with another body. The greater the momentum the
greater the effect on the other bodies and the greater is the force required to stop a body. For example,
when catching a ball the faster it is moving the more force is required to stop it
.
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 STRIKING SITUATIONS
Momentum is also important in striking situations.
The speed at which a baseball is hit depends on the momentum of the bat. When playing baseball, you
can adjust how hard you hit the ball by either changing the velocity of the swing or by using a lighter or
heavier bat (changing the mass). However, a heavier bat will slow down the swing, so you may gain little
advantage.
THIRD LAW-THE LAW OF COUNTER FORCE (LAW OF INTERACTION)
The production of any force will create another force opposite and equal to the first force. For example a
swimmer propels him through the water because the water offers counterforce to oppose the actions of his
hands pushing, allowing him to move. Athletes can jump higher off solid surface because it opposes his
body with as much force he is able to generate, in contrast to sand or other unstable surfaces.
 PRINCIPLES ABOUT PROJECTILES IN SPORTS
Bodies launched into the air that are subject only to the forces of gravity and air resistance are termed
projectiles. Projectiles motion occurs frequently in sport and exercise activities.
Often the projectile involved is an inanimate object, such as a javelin or a golf ball. In some activities the
sports performer becomes the projectile, as in the long jump, high jump, diving and gymnastics. An
understanding of the mechanical factors that govern the flight path or trajectory of a projectile is therefore
important in sports biomechanics.
In other words projectile in sports include objects and other athletes in flight as a result of throwing,
kicking, batting and jumping. If you are a thrower, long jumper, basketball player or any other athlete
whose sport involve objects in flight, there principles about the effects of force on angle, height, impact
and spin can help.
The projectiles predetermined path of fight is influenced by:
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The force applied to it
The angle of release
The height of release
Impact
Spin
The two forces that cause the formation of a parabolic flight path are GRAVITY AND AIR Resistance
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GENERAL INTRODUCTION TO FORCE AND BODY LEVERS
The rotation of a body segment is caused by muscle, providing a force, acting in conjunction with the
skeletal system as a series of levers.
A lever is a “bar or some other rigid structures hinged at a point, and to which forces are applied at two
other points”
It is a simple machine consisting of three components:
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A pivot point (fulcrum)
A weight to be moved (resistance)
Source of energy (effort or force).
 FIRST CLASS OF LEVER
The fulcrum lies between the resistance and the point of effort. Example includes a crowbar, seesaw and
scissor.
Diagram 1
 SECOND CLASS LEVER
Resistance lies between the fulcrum and the point of effort –for example, opening a door using handle;
lifting a wheelbarrow.
Diagram 2
 THIRD LEVER CLASS
The point of effort is between the fulcrum and the resistance.
The force arm = the shortest perpendicular distance between the fulcrum and the application of force =the
effort arm.
The resistance arm = shortest perpendicular distance between the fulcrum and the resistance.
FUNCTIONS OF LEVERS
Levers have two main functions:
(1) To increase the resistance moved by a given effort
This can be done only if the effort arm is greater than the arm-for example, when wielding a
crowbar.
(2) To increase the velocity at which a body moves
This is done by causing it to move a greater distance within time. This can be done only if the
resistance arm is greater than the effort arm – for example, when using a gulf club.
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LEVERS IN THE BODY
 TYPES OF LEVERS
In the body, the fulcrum of the lever is supplied by the JOINT, the resistance is represented by
the BODY PART MOVED, and the effort is provided by MUSCLE PULL AT MUSCLE
INSERTION.
When a muscle contracts to cause motion at a joint, the resulting rotary effect (torque) is a
product of the force and the shortest (perpendicular) distance between the force and the axis of
rotation (fulcrum).
(1)FIRST CLASS LEVERS
First class levers occur in some degree in the body, and many are actions of extending limbs –
for example, the arm or the lower leg
DIAGRAM 2.
(2)SECOND CLASS LEVERS
Second class levers are very uncommon in the body. Two examples are , standing on tiptoes
and closing the lower jaw.
DIAGRAM 3
(3)THIRD CLASS LEVERS
The body is virtually a system of third class levers. Since in third class levers the resistance
arm(RA) is always greater than effort arm (EA), it follows that most the levers are within the
body are more suited to increasing the body’s ability to move quickly than to increasing its ability
to move heavy weights, especially since most force arms are constant in the human body.
The result is that large amounts of effort must be produced by the body to complete tasks
involving the great amount of resistance, which is why it is very important to build up muscle
strength. Weights should be lifted close to the midline of the body to the resistance arm.
On the other hand, the human body is very effective in completing tasks requiring great speed.
DIAGRAM 4
THE END: PREPARED BY: MAKYI D.
HEAD OF DEPARTMENT EXPRRESSIVE ARTS (PHYSICAL EDUCATION
AND SPORTS)
. PLEASE ADD SOME NOTES AND GIVE QUESTION TO LEARNERS FROM SYLLUBUS
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