Biomechanics Flashcards
What is the definition of force?
A push or a pull that alters the state of motion of a body
What is Newtons first law?
A body continues in a state of rest or uniform velocity unless acted on by an external or unbalanced force
What is Newtons second law?
A bodys rate of change in momentum is proportional to the size of the force applied and acts in the same direction as the force applied
What is inertia?
The resistance of a body to change its state of motion whether at rest or while moving
What is veloity?
The rate of change in dispacement
What is Newtons third law of motion?
For every action force appiled to a body there is an equal and opposite reaction force
What is Newtons first law of motion also known as?
The law of inertia
What is Newtons second law of motion known as?
The law of acceleration
What is Newtons third law also known as?
The law of reaction
Sporting example: Newtons first law
A 100m sprinter will remain at rest in the blocks until an external force large enough to overcome the inertia creates motion
Sporting example: Newtons second law
The acceleration of a netball during a chest pass is proportional to the size of the force applied and it will move in the same direction as the force acts
Sporting example: Newtons third law
When a swimmer pushes against thw wall in a tumble turn, the wall applies a force back to the swimmer who then moves in the opposite direction of the action force
Velocity equation
Velocity=displacement/time taken
Momentum equation
Momentum=mass X velocity
Acceleration equation
Acceleration= (final velocity-intial velocity)/time taken
Force equation
Force= mass X acceleration
What is an internal force?
A force generated by the contraction of the skeletal muscles
Example of an intenal force being generated
A sprinter must contract their rectus femoris group to extend their knee and the gastrocnemius to plantar flex the ankle in order to generate the force needed to drive away from the blocks
What is an external force?
A force that comes from outside of the body and acts upon it
Ie weight, friction, reaction and air resistance
What are the 5 effects of force?
- creates motion
- accelerates a body
- decelerates a body
- changes the shape of a body
- changes the direction of a body
What is net force?
The sum of all forces acting on a body
Resultant force
What happens if the netforce is equal to zero?
There is no chnage in motion and forces are balanced.
A body will remain at rest or continue at a constant velocity
What happens if a netforce is present?
There is a chnage in motion as forces are unbalanced.
A body will accelerate, change direction, change shape or decelerate
What are the vertical forces?
Weight and reaction
What are the horizontal forces?
Friction and air resistance
What is the definition of balanced forces?
When two forces acting on a body are equal in size and opposite in direction
What is the defintion of unbalanced forces?
When two forces are unequal in size and opposite in direction
What is the definition of weight?
The gravitational pull that the earth exerts on a body
Weight equation
Weight =ma
What is the defintion of reaction force?
The equal and opposite force exerted by a body in response to the action force placed upon it
What is the defintion of friction?
The force that opposes the motion of two surfaces in contact
What is the defintion of air resistance?
The force that opposes the motion through air
What factors effect friction?
- Roughness of the ground surface
- Roughness of the contact surface
- Temperature
- Size of the normal reaction
How the the roughness of the ground surface affect friction?
By increasing the roughness of the ground surface, friction increases
How the the roughness of the contact surface affect friction?
By increasing the roughness of the contact surface, friction increases
How the the temperature affect friction?
By increasing the temperature of the ground and contact surface, friction increases
How the the size of the normal reaction affect friction?
By increasing the size of the normal reaction, friction is increased
What are the factors affecting air resistance?
- Velocity
- Shape
- Frontal cross-sectional area
- Smoothness of surface
How does velocity affect air resistance?
By increasing velocity, AR inceases
How does shape affect air resistance?
The more aerodynamic the shape the lower the AR
How does frontal cross-sectional area affect air resistance?
By decreasing the cross-sectional area, AR decreases
How does the smoothness of the surface affect air resistance?
By increasing the smoothness of the surface, AR decreases
What is the defintion of streamlining?
The creation of smooth air flow around an aerodynamic shape to minimise air resistance
Vertical forces example
When a gymnast performs a handstand reaction force is equal in size and opposite in direction to weight which acts upwards from the point of contact.
These forces are balanced and so the netforce=0 and body remains at rest
Horizontal forces applied example
When sprinters run on a rubberised track their spikes generate a large frictional force from the starting blocks. Their low tucked body is clad in smooth lycra and moves relatively slowly though the drive phase which minimised air resistance. In this phase of the 100m friction exeeds air resistance. The forces are unbalanced and there is a positive netforce therefore allowing the body to accelerate forward.
What does a free body diagram show?
All of the forces action on a body at a particular instant in time
How does limb kinematics work?
Reflective markers are placed on the performers body and they are filmed using multiple video cameras.
The data is then transferred into the digital form for analysis.
What are the advantages of limb kinematics?
- Allows coaches to use information to change technique and improve performance.
- Examine the effect of movements causing injury
- Used to examine the effectiveness of a training technique
What are the disavantages of limb kinematics?
- Expensive
- Results don’t take individual differences into account
- Happens in a lab so game situations are hard to replicate
Example of how limb kinematics is used
For example: is used when analysing a golf swing, allows the joint and limb to br analysed and evaluate for their effectiveness
What are limb kinematics?
Kinematics is the geometry of the motion of objects which includes displacement, velocity and acceleration.
In simple terms, kinetics studies the forces that cause motion.
What are force plates?
Force plates are platforms that measure all forces applied when a performer stands, steps across or jumps on it
How are force plates used?
The platform measures the ground reaction forces that the performer generates. This can be vertical or both planes of horizontal forces. Data generated including a force time graph, power and acceleration information.
Used for sport biomechanics assessment, gait analysis, balance, rehabilitation and physical therapy.
It is a metal plate, with built in force transducers that produces an electrical output proportional to the force applied, which is displayed in graphical form on a computer.
Sporting examples of when force plates are used?
Walking, running or jumping
Basketball and skating
Whata re the advantages of force plates?
- Fast and accurate results recorded
- Analysis of gait, take off and landing technique
- Results can be used to plan training programmes
What are the disadvantages of force plates?
- Equipment is expensive
- Laboratory conditions make it difficult to perform techniques (eg long jump)
- Limits potential use as they may adapt the way they perform due to laboratory conditions
What are wind tunnels used for?
Used to analyse the amount of air resistance an object is creating whilst in motion.
What are the advantages of using wind tunnels?
It allows engineers to have tight control on environmental variables such as wind speed or wind direction and gives them the ability to crontol cross winds and measure air resistance and flow with percision and accuracy in a very time efficient manner.
What are the disadvantages on wind tunnels?
- Very expensive
- Rewquire complex analysis of the results by research professionals
- Specialised facilities usually only found at engineering bases
Sporting example: wind tunnels
F1 cars are tested in wind tunnels to test the aerodynamic parts and set-ups
What is the definition of centre of mass?
The point at which a body is balanced in all directions; the point from which weight appears to act
Where is a persons centre of mass in an anatomical position?
Around their naval
Where is the centre of mass on a gymnast when performing a somersault?
Outside of the body to act a point of rotation
Explain how a high jumper can move their centre of mass outside of the body to effectively perform the Fosbury flop
The athlete will create a j-curve in their run up to allow for a creater velocity. They will then plant their outside foot to allow their inside leg to lift, along with the arms at take-off to raise the centre of mass a high as possible. They will fully extend their spine to rotate around the bar moving the centre of mass outside their body and below the bar.
This allows the athlete to use less force to take-off but still reach the same height as previous techniques allowed and so when maximum force is generated at take-off, greater heights can be achieved.
What is the defintion of stabilty?
The ability of a body to resist motion and remain at rest or for a body to withstand a force applied and return to its original position without damage.
What are the factors that affect stabiltiy?
- Mass of the body
- Height of the centre of mass
- Base of support
- Line of gravity
How does the mass of the body affect stability?
The greater the mass of the body, the greater the inertia and therefor the greater the stability
How does the height of the centre of mass affect stability?
The lower the centre of mass the greater the stability
How does the base of support affect stability?
The greater the size of the base of support the greater the stability.
Can be moving two points of contact wider apart to create a larger surface area or increasing the number of points of contact
How does the line of gravity affect stability?
The more central the line of gravity to the base of support the greater the gravity
What is the line of gravity?
An imaginary line which extends from the centre of mass downwards to the floor
How does minimising stability benifit a boxer?
When a boxer shifts their centre of mass, they become less stable because it causes their line of gravity to become less central. However this allows them to create more force when punching and faster movements when dodging an opponents punch.
How does a sprinter maximise their stabilty when in the blocks?
Their crouched position gives them a low centre of mass.
They have a large base of support with five points of contact and their line of gravity falls within their base of support. Finally sprinters high muscle mass which increases their stability before coming out of the blocks.
What are two functions of lever systems?
- To generate musclar effort to overcome a given load
2. To increase the speed of a given movement
What are the compents of a lever system?
- lever (bone)
- fulcrum(joint)
- effort(muscular force)
- load(weight or resistance)
What is in the middle of a first class lever system?
Fulcrum
What is in the middle of a seond class lever system?
Load
What is in the middle of a third class lever system?
Effort
What is an example of a first class lever system? Include which each component is
Header in football
Effort= trapezius
Fulcrum=atlas & axis
Load= the weight of the players head
What is an example of a second class lever system? Include which each component is
Long jump take off
Effort= gastrocnemius and soleus Fulcrum= joint between the metatarsals and phalanges Load= the weight of the athlete
What is an example of a third class lever system? Include which each component is
A bicep curl
Effort= bicep brachii Fulcrum= elbow joint Load= the weight held in their hand and the weight of their forearm
What does mechanical advantage allow?
A larger load to be moved with relatively small effort
Effort arm is greater than the load arm
What lever system has mechanical advantage?
Second
What is mechanical disadvantage?
The load arm is longer than the effort arm
What lever system has mechanical disadvantage?
Third
What does mechanical disadvantage cause?
It casues the performer to use a large effor to move a relatively small load.
What are the advantages of a 1st class lever (effort closer to pivot)?
The load moves further than the effort
Ie. Head moves further up & down than the neck muscles contract
What are the disadvantages of a 1st class lever (effort closer to pivot)?
Requires a large effort to move a smaller load
What are the advantages of a 1st class lever (load closer to the pivot)?
Smaller effort will move a larger load
What are the disadvantages of a 1st class lever (load closer to the pivot)?
The load moves shorter distances than the effort
What are the advantages of a 2nd class lever?
Large load can be lifted with relatively little force
What are the disadvantages of a 2nd class lever?
Slower movement
What are the advantages of a 3rd class lever?
Fast movement-load moves further than the effort
What are the disadvantages of a 3rd class lever?
Requires a large effort to move a smaller load
