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biomechanics exam 3
| Question | Answer |
|---|---|
| newtons 1st law | law of inertia: a body will maintain a state of rest or constant velocity unless acted on by an external force that changes that state |
| newtons 2nd law | law of acceleration: a force applied to a body causes an acceleration of that body of a magnitude proportional to the force, in the direction of the force, and inversely proportional to the body's mass. F=ma |
| newtons 3rd law | law of reaction: when one body exerts a force on a second body, the second body exerts a reaction force that is equal in magnitude and opposite direction. assumes equilibrium |
| newtons law of graviation | all bodies are attracted to one another with a force proportional to the product of their masses and inversely proportional to the square of the distance between them. -9.81m/s^2 |
| friction | force acting over the area of contact between two surfaces in the direction opposite of motion or motion tendency. friction= coefficient of friction x normal reaction force |
| coefficient of friction | unitless number serving as an index for the interaction between two surfaces in contact |
| coefficient of static friction | for motionless bodies in contact |
| coefficient of kinetic friction | for moving bodies in contact |
| normal reaction force (R) | force acting perpendicular to two surfaces in contact. weight increases R increases |
| linear momentum | quantity of motion an object possesses M=mv kg*m/s |
| change in momentum | change in mass and/or change in velocity (a vector). newtons 1st law. external force often present |
| momentum equation | m1v1+/- m2v2= (m1+m2)v + same direction - opposite direction |
| impulse | product of force and the time over which the force acts impulse=Ft change in momentum |
| impact | collision characterized by the exchange of a large force during a short time interval |
| perfectly plastic impact | results in the total loss of system velocity. at least one body deforms and doesn't regain its shape, and the bodies don't separate |
| perfectly elastic impact | the velocity of the system is conserved. relative velocities of the two bodies after impact are the same as their relative velocities before impact |
| coefficient of restitution | describes the elasticity between colliding bodies |
| mechanical work | application of force along a displacement. no displacement= no work |
| positive work | when both the net muscle torque and the direction of angular motion at a joint are in the same direction (predominantly concentric contraction) |
| negative work | when the net muscle torque and the direction of angular motion at a joint are in opposite directions (predominantly eccentric contraction) |
| power | rate of work production |
| energy | capacity to do work |
| strain energy (elastic energy) | capacity to do work by virtue of a deformed body's return to its original shape |
| relationship of work and energy | when work is applied to an object/body, the energy of that body/object changes |
| equilibrium | state characterized by balanced forces and/or torques |
| static equilibrium | a motionless state in which sum of torque=0 |
| dynamic equilibrium | concept indicating a balance between applied forces and inertial forces for a body in motion |
| torque | rotary effect of a force about an axis of rotation vector: clockwise- counterclockwise+ |
| moment arm/lever arm | perpendicular distance between the forces line of action and the axis of rotation |
| agonist | prime mover |
| antagonist | control movement velocity |
| when net muscle torque and joint movement occur in the same direction | concentric contraction |
| when net muscle torque is in the opposite direction of joint motion | eccentric contraction |
| net torque is 0 | isometric contraction |
| lever | a simple machine consisting of a relatively rigid object that may be made to rotate about an axis through the application of force |
| axis (fulcrum) | the point of support about which a lever rotates |
| force (effort) | the 'input force' or the force applied to the lever system |
| resistance (load) | the 'output force' or the force of the lever is attempting to move |
| first class levers | lever positioned with the applied force and the resistance on opposite sides of the axis (FAR) |
| second class levers | lever positioned with the resistance between the applied force and the axis (ARF) |
| third class levers | lever positioned with the applied force between the axis and the resistance (AFR) |
| first class lever examples | seesaw, scissors, nodding you head |
| second class lever examples | wheelbarrow, wrench, nutcracker, calf raise |
| third class lever examples | canoe paddle, shovel, broom, moules-bone concentric contractions |
| mechanical advantage | mechanical effectiveness of a lever system, quantified as the ratio of the force arm to the resistance arm |
| stability | resistance to disruption of equilibrium |
| balance | a person's ability to control equilibrium |
| center of gravity | point around which the weight of a body is balanced, no matter how the body is positioned |
| base of support | area bound by the outermost regions of contact between a body and support surfaces |
| angular kinetics: newtons first law | a rotating body will maintain a state of constant rotational motion unless acted on by an external torque |
| angular kinetics: newtons second law | a net torque produces angular acceleration of a body that is directly proportional to the magnitude of the torque, in the same direction as the torque, and inversely proportional to the body's moment of inertia |
| angular kinetics: newtons third law | for every torque exerted by one body on another, there is an equal and opposite torque exerted by the second body on the first |
| moment of inertia | inertial property for rotating bodies, represents resistance to angular acceleration. based on mass and the distance mass is distributed from the axis of rotation |
| angular momentum | quality of angular motion possessed by a body. a change in angular momentum means a change in mass, radius of gyration, and/or angular velocity |
| angular impulse | change in angular momentum, product of torque and the time over which the torque is acting |
| centripetal force | force directed toward the center of rotation for a body in rotational motion |
Created by:
Aylac17