Quiz 6 Flashcards
(31 cards)
what is Fr
- radial force
- any force that causes a body to deviate from its straight-line path
- perp to linear path
Fr equation
- Fr = m x ar
- Fr = mV^2/r
explain centripetal force
- the force keeping the body in the curved path for a body in curvilinear motion
- ex: hammer throw - cable maintains centripetal force, handle released > object flies off in path that is tangential to radius of circle
explain centrifugal force
- force acting on the object once the tension in string is released (hammer throw)
- tendency of an object moving in a circle to travel away from the center of the circle
- acts outward on a body moving around a center
list the 3 factors that would affect the forces on the lower extremities when running around a curve
- Fr is directly proportional to the mass of the runner (heaver the runner = greater the Fr = larger demands on quads (knee extensors))
- Fr is directly proportional to the square of the velocity (faster running speed = greater radial force/speed)
- Fr is inversely proportional to the radius of the curve (larger radius of track = less radial force applied)
describe angle of lean
- angle at which runner has to tilt when measured from vertical
- obtained using the tangent angle (tan 0 = mV^2/r divided by mg = V^2/rg)
what is angle of lean dependent on
- velocity of runner
- radius of curve around which runner moves
why are tracks “banked”
tracks are banked because it causes less stress on the body when running/cycling
- less need for body to increase lean since track is already at an angle
- centripetal force is less on a banked track
define inertia
- the tendency to resist acceleration
- directly proportional to mass of body
- Newton’s 1st Law (Law of Inertia)
define “I”
- moment of inertia: tendency to resist angular acceleration
- I = SUMm x r^2
- sum of all particles composing object x square of radius of each particle from its radius of rotation
- dependent on square of radius > distribution of mass with respect to axis of rotation is more important than amount of mass in determining angular acceleration
how does “I” affect spinning vs summersaulting vs making cartwheels
- spinning: easiest to do because it is easiest to rotate around the vertical axis (motion in the transverse plane) because there is less mass of the body distributed from the axis
- summersaulting: rotation around the horizontal axis, motion in the sagittal plane
- cartwheel: rotation around the horizontal axis, motion in the frontal plane
why do tightrope walkers use long poles
Their rotational inertia increases because the pole increases the mass and distance from the center of rotation which makes it harder to change the person’s rotational state
explain “I” as applied to the examples discussed in class with the human body
- longer moment of inertia = smaller angular acceleration
- I greater when rotated around end vs center
- reduce I by bunting baseball because it pulls bat closer to body and reduces radius of rotation making it easier to swing
- spinning a solid cylinder is easier than hollow cylinder
- bicyclist with hollow front wheel and solid back wheel: back wheel spins easier and faster
explain the principle of conservation of angular momentum (ex: spinning)
- total angular momentum of a system remains constant in the absence of external torques
- ex: spin of an ice skater - angular velocity increases as limb segments are brought closer to the body & decreases as limbs are moved further from axis of rotation; moment of inertia is being manipulate to cause change in angular velocity which allows to conserve angular momentum
angular momentum equation
H = I w
explain the transfer of angular momentum using examples
- volleyball spiking the ball
- cat landing on its feet
- hurdling
explain the differences between equilibrium, balance & stability
- equilibrium: resultant forces and net torques acting upon object are 0
- balance: ability to control current state of equilibrium; implies conscious effort & coordination (neuromuscular function)
- stability: resistance of an object to having its equilibrium disturbed (more stable = more resistance against forces or torques that attempt to disrupt equilibrium)
3 types of equilibrium
- stable: pyramid shaped object placed on its largest side; lower the center of gravity, the longer a torque mist be applied to completely topple the object
- unstable: an object that requires very little force or torque to disrupt its current state
- neutral: object that has no tendency to fall in one direction or the other, moving the object has no tendency to produce either a restorative or disruptive force
identify different types of equilibrium
explain “base of support” and how it applies to different sports
- area enclosed by outermost edges of body in contact with supporting surfaces
- line of the CG must fall within base of support to remain in equilibrium
- a person has balance in the direct proportion to the size of the base
- larger base = more balance
how can center of gravity & center of mass change in the body
how does fluctuations in center of gravity affect performance
what are the different categories of forces that affect motion
- gravitational forces exerted on the body and by external loads
- muscle contractile forces
- elasticity
- contact forces
explain the link system
- movements accomplished by body segments as a result of the summation of forces along the link (kinetic chain and body as a system); starting with GRF
- summation of links = activate the links in a patterned sequence
