BIOMECHANICS Flashcards
VELOCITY
displacement/time
Velocity of a body only changes if an unbalanced force acts on it.
newtons 2nd law
F=ma acceleration is for the body’s centre of mass (CoM). Different parts of the body may have different velocities and accelerations.
momentum
p=mv (kg.m.s-1),
thus force is the rate of change of momentum.
Weight
Weight = mg (newton, N),
weight of a body is the force exerted on it by gravity Where g is assumed to be 9.81 m.s-1
Statics
deals with the equilibrium of bodies. This applies to bodies at rest or in uniform motion when forces and moments do not generate acceleration (i.e. ∑F = 0, ∑M = 0)
Dynamics
Dynamics is concerned with accelerated motion of bodies
work
is done when forces move their points of application W = F.s
Units of J, joules
Power
is the rate of doing work
P = F.s/t = F.u Units of J.s-1, W, watts
potential energy
Lifting a body of mass m through a height of h requires work mgh(J) and increases its gravitational potential energy
P.E. = mgh (J)
kinetic energy
A mass m moving with velocity u has kinetic energy K.E. = 0.5mu2 (J)
walking gait
Gravitational acceleration, g, acts on our centre of mass which moves in the arc of a circle with a radius equal to lower limb length, h, hence
g = u2/h
umax = √gh
Freely chosen speed
≈ 1.2– 1.4 m.s-1
We use an inverted pendulum principle where: mgh and 1⁄2mu2 are 180˚ out- of-phase
(walking faster or slower = forced pendulum)
when walking
KE and GPE are out-of-phase
Max transfer b/w KE and PE is when Froude number (u2/gh) = 0.25 ~60-70% energy of the centre of mass (COM) is conserved in walking
joint moment
Muscles generate force that results in a joint moment
Moment )torque) = f.d (Nm)
Moment arm (d )
= perpendicular distance from the axis of rotation to the line of action of force.
