Forces, Torque Flashcards
what is newtons first law
Inertia
Every object continues in its state of rest or motion in a straight line unless compelled to change that state by external forces acting upon it”
a=F/m
what is newtons second law
“A particle acted upon by an External force moves such that the force is equal to the rate of change of the linear momentum”
Force is proportional to the rate of change in Momentum: F=mv/t=ma
what is newtons third law
“When 2 particles exert force upon one another, the forces act along the line joining particles, and the 2 force vectors are equal in magnitude and opposite in direction”
momentum equation
Momentum (G) = mass x velocity
what is inertia
is a resistance to change in motion
what is mass
direct measure of inertia
an athlete makes a bench press + accelerates the barbell (mass = 100kg) upward to 2ms-2
find the force exerted by the athlete on the barbell during the lift
F = W+ma
F = mg + ma = m (-g) + a)
= 100 x -(-9.81) + 2 x 100
= 1181N
an athlete makes a bench press + accelerates the barbell (mass = 100kg) upward to 2ms-2
after the lift, he lowers the barbell with the acceleration -2ms-2
find the force exerted by the athlete on the barbell during the lowering of the barbell
F = W+ma
F = m(-g) + ma = m (g + a)
= 100 (9.81 - 2)
=781N
what is Friction (f)
Is the force which acts between surfaces and resists the movement
what is the difference between static and dynamic/kinetic friction
S: Force preventing object from moving
vs
D: Force needed to keep object sliding
What is a viscous force
Viscous forces in liquids are smaller than frictional forces between solids
smaller force is needed to peel surfaces in rolling compared to sliding
what happens within a synovial joint
Synovial Joints employ both rolling surfaces and lubricating fluids (synovial fluid to reduce friction
It also has a articular cartilage within joint which has a smooth surface
what µs does a healthy joint have
~0.003
provide the pressure, stress and strain equations
Pressure = Force/ Area
Stress = Force x Area
Strain (deformation) = change in length/ length
what is the Mechanical testing on bone
3 point bending test
Rests on 2 points, stress applied in 3rd (centre)
what happens during the mechanical bone testing
Deformation (bending measured)
Stress strain curve derived
what are the features of a stress strain curve
bending point = yield point
end point = fracture
y axis = stress (load)
x axis = strain (deformation)
what is the process for mechanical testing - tendon
Before load applied (collagen crimped)
Load applied (collagen parallel)
Collagen rupture
what is torque
rotational force produced by muscles, can be demonstrated with a lever arm of muscle action and is a Mechanical advantage
equation for torque
Torque = Force x lever arm = F x r
Measured in Newton metres (Nm)
what are the roles of muscles in movement and how does it help movement
generates torque & angular movements
Muscle force acts on a bone at the attachment point
Generates angular (rotational) movement of the bone
can be modelled using levers
Torque indicates the ability of force to cause a rotation
what is a lever arm
is the shortest perpendicular distance from the line of action of the force (F) to the axis of rotation
what does the plantar flexor muscles do
generate high forces due to small lever arm of their force application
how do you determine what the class of the level arm class and what are they
by the relative position of : Fа/Fʟ/Fulcrum
how to calculate mechanical advantage
with Fа:Fʟ ratio
what is The applied force, Fа
Force of muscles
Attachment point
what is The Load force Fʟ
Weight (m x g) of the forearm and anything being carried
CoM
what is The fulcrum
Centre of the elbow joint
what does the CoM do during motion
Centre of Gravity serves as a reference point for motion produced via muscle acting through levers to provide movement
how is force resolved
into components of vectors
X axis (mechanical axis of the bone, non rotary)
Y axis (rotary component)
describe what the angles of muscles and joint stability tells you
Angle < 90°
Most muscles in the body
Stabilising component, maintaining joint integrity
Angle = 90°
All force is rotary
Angle > 90°
Dislocating component
describe the spinal column
Human spine is made of 24 vertebrae separated by fluid filled disks
what caused back pain
disks can be damaged = spinal nerves compressed = back pain
what % of the population experiences back pain
> 60% back pain
how is the spine modelled
as a liver with small mechanical advantage
Why is the advice for lifting weight to bend knees?
The lever arm of the load force is shorter in b (diagram with legs bent)
what happens when a large force is applied to the lumbosacral disk
last vertebrae from sacrum, bone supporting the spine
what is C1-C7
cervical vertebrae (1)
what is T1-C12
Thoracic vertebrae (2)
what is L1-L5
Lumbar vertebrae (3)
where is the Sacrum
at the very bottom (4)
what is the Finite Element Modelling
builds 3D models from many tiny elements and calculates the response of each to loading
complex modelling often used by biomechanics research
define impulse numerically, graphically, mathematically
Numerically: the product of force and the time it acts
Graphically : the area under a force-time curve
mathematically : the integral of force with respect to time s
