test2 Flashcards
kinetics
the branch of dynamics concerned w the forces that cause or tend to cause motion
law of inertia
every body continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that stage by the forces impresses upon it
law of acceleration
(object will accelerate in direction of force) the change of motion of an object is proportional to the force impressed; and is made in the direction of a straight line in which the force is impressed
law of action reaction
to every action, there is always am opposed and equal reaction: or the mutual action of two bodies upon each other are always equal and directed to contrary parts
law of universal gravitation
all objects attract each other with a gravitational force that is inversely proportional to the square of the distance between objects
what formula is associated with newton’s second law?
EF=ma
impulse
the product of force and the time during which the force acts (change in momentum)
momentum
the product of an objects mass and linear velocity
relation between impulse and momentum
the impulse produced by the net force acting over some duration of time causes a change in momentum of the object upon which net force acts
coefficient if restitution
the absolute value of the ratio of the velocity of separation to the velocity of approach
the relationship between mass and weight
mass is how much matter an object has; weight is mass including the effects of gravity
mechanical work
the product of force and the amount of displacement that occurs in the direction of that force (it is the means by which energy is transferred from one system to another)
positive work
when they contract and their point(s) it attachment move in the direction of the muscle force pulling on them (force and displacement are in the same direction) muscle shortens, contraction is concentric
negative work
when they contract and their pint(s) of attachment (force and displacement in opposite direction); muscle lengthens, contraction is eccentric
in a concentric lift, what kind of work is done?
POSITIVE
in an eccentric lift, what kind of work is done
NEGATIVE
in an isometric lift, what kind of work is done?
no work is done; occurs when a muscle contracts and it’s points of attachment do not move relative to each other- displacement=0 at point of muscle attachment
energy
the capacity to do work
kinetic energy
energy due to motion
gravitational potential energy
energy due to position relative to the earth
strain energy
energy due to deformation of an object
relationship between mechanical work and energy
work- means by which energy is transferred from one object to another; energy- capacity to do work
power
the rate of doing work (how much work is done in a specific amount of time) how quickly or slowly
centric force
change in linear motion; external force that is directed through the center of gravity of an object
eccentric force
change in liberal and angular motion; external force that is not through the center of gravity
torque
the turning (rotation) effects produced by a force- angular and rotary force
counterclockwise torque
positive
clockwise torque
negative
force couple
a pair of external forces that cause change in only the angular motion of an object
relationship of torque and weight training
muscles create the torques that turn our limbs and that pulls on its point of attachment to the skeletal system when it contracts
torque in static equilibrium
the net torque acting on an object must sum to zero to ensure that no changes occur in the angular motion of an object, for an object to truly be in equilibrium, the external forces and external torque (about any axis) must sum to zero
resultant of two or more torques
can add or subtract torques that act around the same axis, just like forces that act in the same direction- in planar situations, we can calculate the net torque by summing the torques that act on an object
center of gravity
the point in a body or system around which it’s mass or weight is evenly distributed or balanced through which the force of gravity acts
center of mass
the point in a body or system of body’s as which the entire mass may be assumed to be concentrated
stability
the capacity of an object to return to equilibrium or its original position after being displaced (not easily moved or thrown off balance)
where should COG be located to maximize stability
should be located within base of support
what happens if the COM falls out of the base of support
the object will fall
estimate the center of gravity on the body
approximately 2.5-5.0cm below your navel (slightly higher than half of your standing height (55-57%)
