Introduction to Biomechanics

Question 1

What is the equation for speed?

Answer 1

Speed (m/s) = distance/time u = dx/dt

Question 2

What is the equation of acceleration?

Answer 2

Acceleration (m/s2) = speed/time

Question 3

What is acceleration?

Answer 3

• Body’s centre of mass (CoM)
• Different parts of the body = different velocities (eg. limbs)
• Energy
  
  • Internal: Energy to move
  • External: Energy associated with COM

Question 4

What is Newton’s 2nd Law of Motion?

Answer 4

Velocity of a body only changes if an unbalanced forces acts on it. F = ma

Question 5

What is momentum?

Answer 5

Force is the rate of change of momentum Momentum = mu

Question 6

What is weight?

Answer 6

Is the force exerted on it by gravity Weight = mg g = 9.81m/s

Question 7

What is statics?

Answer 7

• Bodies at rest
• Uniform motion
• Sum of all forces = 0
• Forces and moments aren’t generating acceleration

Question 8

What is dynamics?

Answer 8

• Accelerated motions of bodies

Question 9

What is joint moments or strength? What are the 3 key components?

Answer 9

1. Muscles generate force that results in joint moment 2. 3. Moment arm (d)= perpendicular distance from the axis of rot. to line of action of force • Muscles cannot push • Generate moments but not necessarily movements • Increasing moment arm (d) will increase the moment (easier)

Question 10

What is work?

Answer 10

When forces move their points of application Work (J) = Fs

Question 11

What is power?

Answer 11

Rate of doing work P = Fu

Question 12

What is GPE?

Answer 12

GPE = mgh m= mass g= gravity h= height lifted

Question 13

What is KE?

Answer 13

KE = 0.5mu2 Mass (m) moving with velocity (u)

Question 14

What is gravitational acceleration?

Answer 14

Acts on centre of mass g = u2/h h = fixed

Question 15

What is the max walking speed for a person?

Answer 15

• Freely chosen speed of 1.2-1.4m/s
• Most economic speed
  
  • Inverted pendulum prinicle
    
    • Walking faster or slower = forced pendulum
    • Costs more energy
    • Out of natural speed
• Limb is vertical - CoM is highest, slowest
  
  • GPE is highest
  • KE is lowest
• Limb is most far apart (step phase) - CoM is lowest, fastest

Question 16

Why is walking energetically cheap?

Answer 16

• Max transfer between KE and GPE is when Froude’s number (u2/gh) is 0.25 • 60-70% energy of CoM is conserved in walking • 30% by muscles

Question 17

What is the importance of knowing material properties of tissue?

Answer 17