Forces, Torque

Question 1

what is newtons first law

Answer 1

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

Question 2

what is newtons second law

Answer 2

“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

Question 3

what is newtons third law

Answer 3

“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”

Question 4

momentum equation

Answer 4

Momentum (G) = mass x velocity

Question 5

what is inertia

Answer 5

is a resistance to change in motion

Question 6

what is mass

Answer 6

direct measure of inertia

Question 7

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

Answer 7

F = W+ma
F = mg + ma = m (-g) + a)
= 100 x -(-9.81) + 2 x 100
= 1181N

Question 8

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

Answer 8

F = W+ma
F = m(-g) + ma = m (g + a)
= 100 (9.81 - 2)
=781N

Question 9

what is Friction (f)

Answer 9

Is the force which acts between surfaces and resists the movement

Question 10

what is the difference between static and dynamic/kinetic friction

Answer 10

S: Force preventing object from moving
vs
D: Force needed to keep object sliding

Question 11

What is a viscous force

Answer 11

Viscous forces in liquids are smaller than frictional forces between solids
smaller force is needed to peel surfaces in rolling compared to sliding

Question 12

what happens within a synovial joint

Answer 12

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

Question 13

what µs does a healthy joint have

Answer 13

~0.003

Question 14

provide the pressure, stress and strain equations

Answer 14

Pressure = Force/ Area
Stress = Force x Area
Strain (deformation) = change in length/ length

Question 15

what is the Mechanical testing on bone

Answer 15

3 point bending test
Rests on 2 points, stress applied in 3rd (centre)

Question 16

what happens during the mechanical bone testing

Answer 16

Deformation (bending measured)
Stress strain curve derived

Question 17

what are the features of a stress strain curve

Answer 17

bending point = yield point
end point = fracture
y axis = stress (load)
x axis = strain (deformation)

Question 18

what is the process for mechanical testing - tendon

Answer 18

Before load applied (collagen crimped)
Load applied (collagen parallel)
Collagen rupture

Question 19

what is torque

Answer 19

rotational force produced by muscles, can be demonstrated with a lever arm of muscle action and is a Mechanical advantage

Question 20

equation for torque

Answer 20

Torque = Force x lever arm = F x r
Measured in Newton metres (Nm)

Question 21

what are the roles of muscles in movement and how does it help movement

Answer 21

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

Question 22

what is a lever arm

Answer 22

is the shortest perpendicular distance from the line of action of the force (F) to the axis of rotation

Question 23

what does the plantar flexor muscles do

Answer 23

generate high forces due to small lever arm of their force application

Question 24

how do you determine what the class of the level arm class and what are they

Answer 24

by the relative position of : Fа/Fʟ/Fulcrum

Question 25

how to calculate mechanical advantage

Answer 25

with Fа:Fʟ ratio

Question 26

what is The applied force, Fа

Answer 26

Force of muscles
Attachment point

Question 27

what is The Load force Fʟ

Answer 27

Weight (m x g) of the forearm and anything being carried
CoM

Question 28

what is The fulcrum

Answer 28

Centre of the elbow joint

Question 29

what does the CoM do during motion

Answer 29

Centre of Gravity serves as a reference point for motion produced via muscle acting through levers to provide movement

Question 30

how is force resolved

Answer 30

into components of vectors
X axis (mechanical axis of the bone, non rotary)
Y axis (rotary component)

Question 31

describe what the angles of muscles and joint stability tells you

Answer 31

Angle < 90°
Most muscles in the body
Stabilising component, maintaining joint integrity

Angle = 90°
All force is rotary

Angle > 90°
Dislocating component

Question 32

describe the spinal column

Answer 32

Human spine is made of 24 vertebrae separated by fluid filled disks

Question 33

what caused back pain

Answer 33

disks can be damaged = spinal nerves compressed = back pain

Question 34

what % of the population experiences back pain

Answer 34

> 60% back pain

Question 35

how is the spine modelled

Answer 35

as a liver with small mechanical advantage

Question 36

Why is the advice for lifting weight to bend knees?

Answer 36

The lever arm of the load force is shorter in b (diagram with legs bent)

Question 37

what happens when a large force is applied to the lumbosacral disk

Answer 37

last vertebrae from sacrum, bone supporting the spine

Question 38

what is C1-C7

Answer 38

cervical vertebrae (1)

Question 39

what is T1-C12

Answer 39

Thoracic vertebrae (2)

Question 40

what is L1-L5

Answer 40

Lumbar vertebrae (3)

Question 41

where is the Sacrum

Answer 41

at the very bottom (4)

Question 42

what is the Finite Element Modelling

Answer 42

builds 3D models from many tiny elements and calculates the response of each to loading

complex modelling often used by biomechanics research

Question 43

define impulse numerically, graphically, mathematically

Answer 43

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