Transcript Fundamentals of Biomechanics

Fundamentals of Biomechanics
Biomechanics
• Applying the concepts of physics and
mechanics to the way the body moves and
how it applies force to itself and other objects
• Understanding biomechanics can help
improve performance and reduce injuries in
sport
Kinematics
• The study of motion, change in position of the
body or object
–
–
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Linear- motion in a straight line
Curvilinear- motion in a curve
Angular- motion around an axis
General- linear and angular motion together
• Activity- In small groups come up with two
sporting examples for all types of movement
listed above.
Vector vs. Scalar
• Vector- a measurement that has both size and
direction
– Example: Displacement, Velocity
• Scalar- a measurement that only has size
– Example: Distance, Speed
Linear and Angular Kinematics
• Displacement vs. Distance
• Velocity vs. Speed
• Acceleration
Displacement vs. Distance
• Displacement- the change of position of the
body or an object from one place to another
– Involves both distance and direction
• Linear- Movement in a Straight Line (Horizontal,
Vertical, Lateral)
• Angular- difference between start and finish when
moving around an axis
• Distance- measure of how far a person or
object travels
– Has no direction
Velocity and Speed
• Velocity- change in displacement divided by
he time it takes for the change to occur
– Speed is the size of linear velocity
• Speed = distance moved
time taken
v=s
t
• Angular Velocity is the change in angular
displacement divided by the time for the
change to occur.
Acceleration
• Acceleration- change in velocity divided by the
time for the change to occur
– Can be a change in speed, change in direction or
combination of both
• Acceleration = change of speed per second
– a= v – u (starting velocity)
t
• Angular acceleration is the change in angular
velocity divided by the time for the change to
occur
Role Review
1. Describe the difference between a vector and
a scalar
2. Define the following terms
1. Velocity
2. Displacement
3. Acceleration
Force
• Using the IPADs research and define Newton’s
Three Laws of Motion
• Provide and example for each of the three
laws
Newton’s First Law of Motion
• An object at rest will remain at rest unless
acted on by an unbalanced force. An object in
motion continues in motion with the same
speed and in the same direction unless acted
upon by an unbalanced force.
• Sometimes called the Law of Inertia
Newton’s Second Law of Motion
• Acceleration is produced when a force acts on a mass. The
greater the mass (of the object being accelerated) the greater
the amount of force needed (to accelerate the object).
• Second Law gives us an exact relationship between force,
mass, and acceleration. It can be expressed as a mathematical
equation:
– FORCE = MASS times ACCELERATION
• F= m x a (Answer expressed in Newtons)
Newton’s Third Law of Motion
• For every action there is an equal and
opposite re-action
• for every force there is a reaction force that is
equal in size, but opposite in direction.
Role Review
• In your own words and to the best of your
recollection, describe Newton’s Three Laws of
Motion
Sample Problems
1. How much force must be applied by a kicker
to give a stationary 2.5-kg ball an
acceleration of 40m/s/s?
2. A high jumper with a body weight of 712 N
exerts a force of 3000 N against the ground
during takeoff. How much force does the
ground exert on the high jumper?
Measurement of Force
• Force is measured in Newtons (N)
– Defined as the force which produces an
acceleration of 1 metre per second squared in a
mass of 1 kilogram.
Weight and Gravitational Field
• Gravity is an example of a force field
– Force can be exerted on an object without
touching
– Field exerts a force of 9.81 N kg. (Can be
approximated to 10 N kg for calculations
purposes)
– Example: force exerted on 100kg would be 1000 N
Weight vs. Mass
• In scientific terms weight and mass are not the
same
• Mass- same everywhere for a given object.
Does not change with the gravitational field
– Inertia- resistance to acceleration. More inertia an
object has the harder it is to accelerate.
• Weight- force due to the gravitational field
and changes with Gravity
– Weight= mass x gravity field strength
Weight and Mass Practice Problems
1. A runner has a mass of 68 kg. Calculate the
runners weight.
2. A football player has a weight of 850 N.
Calculate the players mass.
3. A basketball player with a mass of 72 kg
jumps off the ground with a force of 2600 N.
What is the players net force?
Reaction Forces
• Produced as a result of Newton’s Third Law of
Motion
– Reaction forces on the ground caused when
athlete pushes hard downward on the ground.
Force in the opposite direction pushes up on the
athlete
– Reaction forces can also be applied to the impact
between sportsperson and an object. (ex. golf,
soccer, tennis racket)
Reaction Force-Practice Problems
1. A golf ball weighing 0.5kg is hit with an initial
velocity of 74 m/s. What is the force exerted
on the golf ball at impact? At impact how
much force is exerted against the club?
2. A 70 kg long jumper lands in the sand with a
force of 2800 N. Calculate the net force
exerted on the jumper. What is the rate of
deceleration?
Work, Energy and Motion
• Work= force x distance moved in the direction
of force.
• Kinetic Energy – mechanical energy possessed
by a moving object or body by virtue of
motion
– KE = ½ x mass x (velocity)2 (Answer in Joules)
Example: Shot Put
Momentum Basics
• Momentum is another vector measurement.
Momentum is in the same direction as velocity.
• Scientists calculate momentum by multiplying the
mass of the object by the velocity of the object. It
is an indication of how hard it would be to stop
the object.
– If you were running, you might have a mass of 50
kilograms and a velocity of 10 meters per second west
(really fast). Your momentum would be 500 kg-m/sec
west. Easy as pi
Momentum and Impulse
• Momentum- the property an object has due
to its movement.
– P= m x v (P=momentum, M= Mass V= Velocity)
• Impulse- force multiplied by the time it acts
– Impulse = F x t (F=Force, t = time)
Momentum-Impulse Relationship
• Linear impulse = change in linear momentum
– Size and direction of change of momentum
depends on the force acting upon it and for how
long
– Example- Bat hitting a baseball
• Impulse = change of momentum
– F x t = change of (m x v)
Levers and Centre of Mass
Levers
• Internals Forces- forces exerted on one part of
the body on another.
– When muscle contracts origin and insertions are
pulled together
• Ex.- Bicep Curl
Class 1 Lever
• The fulcrum lies between the effort and the
load
– Ex. Skull-Neck, Tricep-Elbow Joint
Class 2 Lever
• Lever where the fulcrum is at one end, the
effort at the other and the load lies between
them.
Class 3 Levers
• Levers where the fulcrum and load are at
opposite ends with the effort in the middle
– Effort is always larger than the load because the
effort is nearer the fulcrum
– Most common type of levers found in the human
body
Levers
Torque (Moment)
• If force applied to an object that is free to
move around an axis then torque is created
– Sometimes referred to as Moment of Force
Equation: Moment of Force= force x distance to fulcrum (Nm)
Size of the Torque depends on
1. the size of the force
2. the direction of the force
3. how far the force is applied from axis
Biomechanics and Force
• Does a persons biomechanics effect their
ability to create force? Explain
• In partners brainstorm 1 sporting events
where a person with shorter limbs would have
a mechanical advantage and 1 sport where a
person with longer limbs would have a
mechanical advantage. Explain your answers.
Centre of Mass
• Using your course companions pgs. 96-98
complete the following questions
1. Define Centre of Mass
2. Describe factors that will effect where the centre
of mass lies within an individual
3. List three reasons why knowing the centre of
mass is important.
Group Role Review
• In small groups complete the following two questions.
(Use diagrams to help)
• 1. Describe and apply Newton’s second and third laws
of motion to a sprinter leaving the starting blocks.
• Define Newton’s Laws (Include Reaction Force)
• Provide a detailed description or diagram to represent your
answer
• 2. Describe the relationship between impulse and
momentum on a high jumper
• Define both terms (impulse and momentum)
• Apply terms to the approach and jump
Centre of Mass
1. How might body position effect a persons
centre of mass. (Refer to Definition) Explain
your answer.
2. In groups brainstorm and record sports
where the centre of mass remains within the
body throughout the movement and
activities where the centre of mass
temporarily lies outside the body.
Centre of Mass
Projectile Motion
• In groups throw four objects, a tennis ball, a
softball, a table tennis ball and a birdie with
the same velocity and height of release
– Draw the approximate flight path of each
– Brainstorm all the factors that affect the flight
path and distance for each of the items used.
– Describe how spin may effect both flight path and
distance
Rotating Systems
Rotating Systems
• Angular Displacement- similar to linear
displacement, the elative angle compared to
some fixed position or line
– Ex. – Golf Swing from starting position
• Measured in radians
– 1 degree = 0.017453 Radians
Moment of Inertia
• Is the resistance to rotational motion
– The bigger the moment of inertia the larger the
moment of force to provide angular acceleration
– Same as linear situation but instead of moving in a
line, object or body moves around an axis
Brainstorm
• When thinking about an object or body
rotating around an axis, what factors will
effect the moment of inertia? Explain your
answers.
• Apply those factors to different sporting
activities.
Angular Momentum
• Angular Momentum is defined as:
• Angular velocity X moment of inertia
• Enables explanation of why the rate of spin
changes when the moment of inertia changes
– Law of Conservation of Angular Momentum
Law of Conservation of Angular
Momentum
• Law states that “the angular momentum of a
system remains constant throughout a
movement provided nothing outside the
system with a turning moment acts upon it”
(Davis et.al)
– Ex.- a skater already spinning changes their
moment of inertia (changing body position), then
the rate of spin will also change
Angular Velocity
• Angular Velocity is defined as:
– Angular Velocity = angle turned (in radians)
time taken to turn
• Concept applies to situations where rate of
spin changes with time
– Ex. hammer throw