biomechanics Flashcards
what is kinetics?
- study of forces associated with motion of a body
what is kinematics?
- concerned with description of motion
what is linear motion?
- something travelling the same direction and distance over same time
what is rectilinear?
- all parts moving in same direction at the same time
what is curvilinear?
- when an object moves the same distance over the same time in a curve
what is angular motion?
- movement that occurs around an axis of rotation
what is general motion?
- combination of angular and linear motion
what are spatial reference systems?
- allows you to track athletes position over time
- describes where diff parts of body have moved
what are scalars?
- described by magnitude
e.g. speed, distance, volume
what are vectors?
- described by magnitude and direction
e.g. velocity, force, acceleration
what is force?
- push/ pull which enables us to start, stop, change direction or maintain balance
what do arrows on diagrams represent? describe the length, line of application+ point of application
- force
- length= magnitude
- line of application = direction
- point of application= where force originated from
how do you work out force?
force = mass x acceleration
- measured in newtons
what are tensile forces? give an example
- pulling forces on ends of an internal structure
e.g. muscles onto tendons onto bones
what are the main force generating mechanisms?
- muscles as they form cross bridges and contract to pull tendons which attach to bones
what are compressive forces? give an example
- pushing forces acting on ends of an internal structure
- bones onto cartilage onto bones
what do free body diagrams represent?
- all external forces acting on an object; external force is the result of all interactions with other objects and surrounding environments
what are external forces? what are the two types?
- act on an object as a result of its interactions with the environment
- contact and non- contact
what is a contact force? give an example
- when objects touch e.g. ground reaction force
what is a non- contact force? give an example
- when objects don’t touch e.g. gravity
what are colinear forces?
- multiple forces applied in same line of action
e.g. tug of war - applied in same or opposite direction
what is resultant force?
- vector sum of all forces (2+)
what is the net force?
- combination of all forces acting on an object
- how all external forces act on the object and their vector addition
what is a concurrent force?
- forces acting through a single point but on different lines
what is the weight?
- force of gravity acting on an object
- measured in newtons
how do you work out weight?
weight= mass x acceleration due to gravity
what is newton’s law of gravity? what is gravitational force inversely proportional to?
- earth exerts some gravitational force which accelerates object towards the ground
- all objects attract each other with a gravitational force inversely proportion to square of distance between them and proportional to mass of each of two bodies
what is acceleration due to gravity in newtons?
9.81 newtons = 1kg x 9.81ms- 2
what is mass?
- how much stuff is present in the object
how should you study movement?
- treat one aspect of body as being the object
- isolate segment of interest
if force in muscle is bigger than external force applied downwards, what happens?
- flexion occurs
what is the centre of gravity? what does it follow?
- point where the weight of an object is balanced
- follows direction you move in
- average point where all mass congregates
why is centre of gravity varied?
- body composition
- gender
- someone with long legs/ muscular arms have higher COG compared to short stockier legs
what happens to COG if object moves position?
- COG moves in direction from which mass is distributed
what happens to COG when lifting arms?
- COG is raised as more mass and weight is oriented upwards
what happens to COG when you bend over? describe an example
- COG moves outside body e.g. Fosbury flop; manipulates COG under body to improve technique of arching
- forces we generate pushes into air and max force determines how centre of gravity can reach
what is the centre of mass?
- weight of an object acts as a single point
- indicates where point of application of force is; applies a force in same direction as weight
what are newtons laws used to predict?
- consequences of forces on human movement
what is Newton’s first law? describe
- law of inertia; object will remain moving at constant speed unless acted on by external force
what is static equilibrium?
- if acceleration is zero then velocity doesn’t change ; object in constant state of motion as forces are balanced
what happens if an object is in motion and the external forces are balanced?
- object will continue to move and acceleration will be 0m/s/s as it moves in same way
what is linear momentum?
- object’s mass and its linear velocity
how do you work out linear momentum?
linear momentum (p) = mass (m) x linear velocity(v)
- measured in kgm/s
what does more momentum of an object mean? what is curve of change in momentum same as?
- more momentum of an object means it’s harder to stop it moving
- curve is the same as curve of change in velocity ; only difference in mass
what is an unbalanced force?
- net force isn’t zero so acceleration occurs in direction of net force
how does mass affect inertia?
greater mass means greater inertia
what is newton’s second law?
- law of acceleration; net external force must be acting on an object in order to accelerate
what is the law of acceleration a relationship between?
- object’s mass, net external force experienced and acceleration
how does mass affect acceleration?
larger mass causes slower acceleration
what is newton’s third law?
- law of action- reaction
- every force has an equal and opposite reaction
describe walking stages relating to vertical forces
- vertical forces experienced on foot are similar during heel contact and toe off
- heel strike= negative horizontal force
- toe off= positive horizontal force
what is the impulse at the heel strike and toe off?
heel strike= impulse is negative so acts in backwards direction ; reduces momentum
toe off= impulse is positive so acts in forwards direction ; increases momentum (sped up)
what is impulse?
- equal to area under the force- time graph
- represents a net external force and hence produces change in momentum
what does negative impulse cause?
- reduces momentum
how do you work out impulse?
impulse = force x time
impulse (force x time) = momentum (mass x velocity)
when dealing with people what stays the same so what does change in impulse represent?
- mass stays the same
- change in impulse is represented by change in velocity
what is net force equal to? give an example
- time, rate, change and momentum of system
- hitting a ball with a bat occurs over a period of time; impulse is force multiplied by time
how to land a jump relating to velocity and momentum?
- reduce velocity to zero and hence decrease momentum
- extends the balls of the feet forwards
what is the landing distance?
- change in height from the moment you first touch the ground to moment your hips are your centre of mass
- stops continuously moving downwards
what is the landing time?
amount of time between these two events; time is generally longer when distance is longer
what is the difference between stiff landing and soft landing?
stiff landing= force is experienced over a short period of time
soft landing = force is experienced over a longer length of time
