Biomechanics Flashcards
What is force?
what can it do?
> a push or pull that alters, or tends to alter, the state of motion of a body.
Functions:
- cause a body at rest to move
- cause a moving body to change direction, accelerate or decelerate
- make an object change shape
Define Inertia
The resistance of a body to change its state of motion whether at rest or while moving
Define Velocity
The rate of change is displacement. This is related to speed and includes a directional element
Define Acceleration
The rate of change in velocity.
Acceleration (m/s/s) =
(final velocity - initial velocity) / time
Define Momentum
The quantity of motion possessed by a moving body.
Momentum (kgm/s) = mass x velocity
What is Internal Force?
> generated by the concentration of skeletal muscle
- a 100m sprinter must contract the rectus femoris to extend the knee and gastrocnemius to plantar flex the ankle to generate the force required to drive out of the blocks
What is External Force?
> comes from outside the body and acts upon it.
can be weight, reaction, friction and air resistance
What 5 effects can force have?
E.G. Penalty Kick in Football
- can create motion - ball remains at rest until a force is applied to make it move.
- can accelerate a body - greater the force applied by the foot, the greater the acceleration towards goal.
- can decelerate a body - ball moving through air resistance will slow down
- can change direction of the body - goalkeepers hand saving the ball and pushing it away from goal
- can change the shape of a body - as the ball hits the net it will make the shape of the net change.
Define Net Force
The sum of all forces acting on a body, also termed resultant force. It is the overall force acting on a body when all individual forces have been considered
Define Balanced Forces
These occur when two or more forces acting on a body are equal in size and opposite in direction.
Net force = 0, the body will remain at rest or in motion with constant velocity
Define Unbalanced Forces
These occur when two forces are unequal in size and opposite in direction.
A net force will present and the body body will change its state of motion, either accelerating or decelerating
Define Weight
The gravitation pull that the earth exerts on a body.
Weight (N) = mass x acceleration
How does Weight class as a Vertical Force?
.> Weight is the gravitational pull that the earth exerts on a body
> measured in newtons
> weight force is always present and acts downwards from the bodys centre of mass
Define Reaction
The equal and opposite force exerted by a body in response to the action force placed upon it
How does Reaction class as a Vertical Force?
> reaction is the equal and opposite force exerted by a body in respose to the action placed upon it and measured in Newtons (N)
Third Law - it is always present when two bodies are in contact
normal reaction can be shown on a diagram with an extending arrow upwards from the point of contact with the surface
Define Friction
The force that opposes the motion of two surfaces in contact
How is Friction classed as a Horizontal Force?
> friction is the force that opposes the motion of two surfaces in contact and is measure in newtons
a sprint cyclist tyres would tend to slip backwards as they rotate; friction opposed this and acts forwards
shown on a diagram by horizontal arrow extending in the same direction as the motion form the point of contact parallel to the sliding surface.
What’s newtons first law?
law of intertia
- a body continues at a state of rest unless a force is acted upon it.
- the greater the mass, the greater the inertia
Apply newtons first law to a penalty kick in football?
Newtons first law tells us that a body remain at rest unless a force acts on it. Therefore, a football stays on the spot until kicked by a football.
what’s newtons second law?
law of acceleration.
- ‘When a force acts on an object, the rate of change in momentum
experienced by the object is proportional to the size of the force and takes place in the direction in the which the force acts’
What’s an example of newtons second law?
The speed and direction of the football isdependant upon the size of force applied by the foot:
- A footballer that only needs to pass the ball a short distance will apply a relatively small amount of force in the direction of his teammate to make
a successful pass. - If the player is further away then a greater force
is required to pass over the longer distance
What’s newtons third law?
All actions have an equal and opposite reaction
what’s an example of newtons third law?
rugby conversion:
A forward and upward action is applied to the ball from the foot. The ball will apply an equal and opposite down and backward reaction force to the foot.
Define reliability
The extent to which an experiment, test or
measuring procedure gives the same
results after repeated trials
Define validity
How well a test measures what it claims to measure. It is important for a test to be valid in order for the results to be
accurately applied and interpreted
What are limb kinematics and what do they do?
- Study of movement in relation to time and space.
- 3D or optical motion analysis records an athlete performing a sporting action.
- Analyses joint and limb efficiency with measurements of bone displacement,
velocity and acceleration in multiple planes of movement. - coaches use these to adjust specific limb placement ad technique
What are force plates?
- Ground reaction forces can be measured in lab conditions using force plates.
- Data from the athlete balancing, running or jumping can be used to assess the size and direction of the force.
- Used for gait analysis, walking, running, balance and rehabilatation.
What do we use force plates for?
- Assess an athletes posture and help with alignment issues to cure pain
- Improve balance to help with athletes who need to hold a static position, e.g. netballer holding a position to mark the ball
- Rehabilitation from injuries and help speed up recovery
- Measure force, power and acceleration and assess/improve the best technique
- Optimise angle of take off and improve technique
- Reduce/prevent injuries, e.g. when bowling a cricket ball
- Help with the development of protheses athletes
What are wind tunnels?
- Wind tunnels are created from a large fan at the end of an enclosed tunnel.
- Objects such as bikes and helmets can be measured by blowing coloured
smoke through the tunnel and assessing how it passes the object. - Small changes can be made to the shape and thus improve the aerodynamics.
- Very specialised equipment, very expensive and requires complex analysis of the results.
Define centre of mass
The point at which a body is balanced in all directions; the point from which weight appears to act
- Its location is dependant on the distribution of body mass and can be manipulated to improve sporting technique.
Define stability
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
Factors that affect stability
- Mass of the body
- Height of the centre of mass
- Base of support
- Line of gravity
Stability; mass of a body
Greater the mass, greater the inertia, therefore the greater the stability.
E.g. a prop in rugby has a high mass to withstand the applied forces
Stability; height of CoM
Lower the Com, greater the stability.
E.g. when a gymnast lands they flex at the hip and knee to lower their CoM
and have a stable landing
Stability; base of support
Greater the BoS, greater the stability. Can be achieved by moving two points of contact wider apart to create a larger surface area or increasing the number of points of contact.
E.g. wrestlers stand with a wider base
Stability; line of gravity
The imaginary line that extends down from the CoM. The more central the
line is, the greater the stability.
E.G. A netball shooter has line between her base, whereas a GK has hers outside and will often over rotate and fall forward.
What are lever systems?
Lever systems are the coordination of our bones and muscles, primarily to create human movement.
What are the 2 main functions of lever systems?
- Generate muscular effort to overcome a given load
- Increase the speed of a given
movement
What’s the first class lever?
Effot - Fulcrum - Load
E.G. Extension of the neck when preparing to head a football.
What’s the second class lever?
Effort - Load - Fulcrum
E.G. Standing on ball of the foot in the take off phase of a high jump
What’s the third class lever?
Load - Effort - Fulcrum
E.G. Flexion of elbow during a bicep curl
What’s the moment of force?
The turning force of the effort/load about the fulcrum can be calculated.
Moment of Force (Nm) =
Force (N) x perpendicular distance of the force from the fulcrum (m)
Define mechanical advantage
Second class lever systems where the effort arm is greater than the load arm. A large load can be moved with a relatively small effort
Define mechanical disadvantage
Third class lever systems where the load arm is greater than the effort arm. A large effort is required to move a relatively small load.
