biomechanics finals review

List and briefly explain the 3 primary factors affecting the stability of an object

1. Mass -- the more massive something is, the more force needed to change it's motion. property of inertia.

2. Base of Support -- area/region bordered by body parts in contact with the ground. The larger our BOS, the more stable we will be. To be stable, a person's CG must fall within the BOS. EX: make your stance wider (BOS larger) when the train is coming to a stop to be stable

3. Center of Gravity Height -- the lower the body CG, the more force necessary to topple it. A taller person is easier to knock over because the lower and wider we are, the more stable we tend to be

balance

the active process by which a person controls equilibrium

stability

a byproduct of our body structure and how we situate the position of our bodies

Guidelines for the Incorporation of Unstable Apparatus into a Resistance-Training Program

Humans cannot generate as much force on unstable apparatus so we need to alternate training. Some days train in a stable environment, some days train using unstable apparatus (EX: single leg DL, swiss ball, wobble board)

Describe the potential limitations associated with elastic band resistance training.

Last several degrees in natural weighted environment (top/end of ROM) causes active deceleration. This cannot occur when using elastic bands since the movement is hardest at the top/end of ROM.

coefficient friction

mu = fL / N

coefficient elasticity

mu = fS / N

Formula for WORK

W = F x D

Negative Work

1/3 the work of stepping UP

kinetic energy

moving energy

elastic potential energy

EX: the position a person lands in when absorbing shock BEFORE bouncing back up from a box jump

gravitational potential energy

the energy an object possesses due to its position in a gravitational field

EX: standing on a ledge right before falling off of it

Where is Center of Gravity Height located?

55-56% of the standing height, just below the belly button

What does the location of the CG mean and its implications of its position for movement?

The CG is the point about which we would rotate when free from gravity and the point at which we would balance if placed on a fulcrum

What is the optimal arrangement of CG and BOS for ACCELERATION?

CG must be displaced FORWARD of BOS

What is the optimal arrangement of CG and BOS for DECELERATION?

CG must be displaced DIRECTLY BEHIND BOS

What is the optimal arrangement of CG and BOS for MAINTAINING and MAXIMUM SPEED?

CG must be directly ABOVE BOS

What are the three physiological mechanisms governing standing balance?

1. inner ear - monitors changes in the position and velocity of the head

2. extensor thrust reflex - in the ball of the foot

3. stretch reflex - in the postural muscles (EX: calves)

Bernoulli's Principle

states that there is an INVERSE RELATIONSHIP between PRESSURE and VELOCITY of a fluid

-- low pressure vacuum = high fluid velocity
-- high pressure vacuum = low fluid velocity

magnus effect

ball/object will curve or swing in direction of lowest pressure/highest velocity, generated by spin

What are the factors affected both the drag and lift encountered by an object?

1. Velocity -- The higher the velocity, the more drag and lift an object will encounter.
2. Pressure -- The higher the pressure, the more drag an object experiences. The greater differential between high and low pressure improves lift.
3. Angle of incidence

What is meant by the elastic limit of a tissue?

body tissue gets stretched beyond the point where it can regain/return to original shape

EX: rolling an ankle -- ligaments will now forever be elongated

What is the stall angle of a projectile? AKA - What causes it?

occurs when drag exceeds lift, which happens when the optimal angle of attack is exceeded

EX: for discus, stall will occur at 24-26 degrees

How can you make an object more STREAMLINED?

give it a tail to prevent turbulence at the back OR give its skin hexagonal dimples