force

(noun)

Any influence that causes an object to undergo a certain change concerning its movement, direction, or geometrical construction.

Related Terms

  • orce-Velocity Relationship
  • Force-Length Relationship
  • Force-Velocity Relationship
  • resting length
  • power
  • Shortening velocity

Examples of force in the following topics:

  • Velocity and Duration of Muscle Contraction

    • The shortening velocity affects the amount of force generated by a muscle.
    • The force-velocity relationship in muscle relates the speed at which a muscle changes length to the force of this contraction and the resultant power output (force x velocity = power).
    • The force generated by a muscle depends on the number of actin and myosin cross-bridges formed; a larger number of cross-bridges results in a larger amount of force.
    • Though they have high velocity, they begin resting before reaching peak force.
    • As velocity increases force and power produced is reduced.
  • Force of Muscle Contraction

    • The force a muscle generates is dependent on its length and shortening velocity.
    • The force-velocity relationship in muscle relates the speed at which a muscle changes length with the force of this contraction and the resultant power output (force x velocity = power).
    • The force generated by a muscle depends on the number of actin and myosin cross-bridges formed; a larger number of cross-bridges results in a larger amount of force.
    • As velocity increases force and therefore power produced is reduced.
    • Although force increases due to stretching with no velocity, zero power is produced.
  • Motor Units

    • There are often multiple sizes of motor unit within a motor pool as a means of modulating the precision and force produced by a single muscle.
    • For example, a small motor unit in the biceps can be activated for small precise movements, while a larger motor unit can be activated to facilitate more forceful actions.
    • These multiple motor units of different sizes within a motor pool allow for very fine control of force either spatially or temporally.
    • Spatial – The recruitment of more or larger motor units to increase force.
    • Temporal – The repeated stimulation of a motor unit so that the force of contraction generated is summed.
  • Lever Systems

    • A large but relatively small force can move a heavy object.
    • Levers can also vary based on the relative position of the load, pivot and point of force application.
    • In a first class lever, the load and force sit on either side of the pivot like a seesaw.
    • In a second-class lever, the force is applied at one end with the pivot at the other and the load in between.
    • In a third-class lever the force is applied between the load and the pivot.
  • Glomerular Filtration

    • The force of hydrostatic pressure in the glomerulus (ie. the force of pressure exerted from the pressure of the blood vessel itself) is the driving force that pushes filtrate out of the capillaries and into the slits in the nephron.
    • Osmotic pressure (ie. the pulling force exerted by albumins) works against the greater force of hydrostatic pressure, and the difference between the two determines the "effective pressure" of the glomerulus which determines the force by which molecules are filtered.
  • Introduction to Blood Pressure

    • Blood pressure is a vital sign, reflecting the pressure exerted on blood vessels when blood is forced out of the heart during contraction.
    • The pressure originates in the contraction of the heart, which forces blood out of the heart and into the blood vessels.
    • Therefore, the systolic pressure will show the pressure that your heart emits when blood is forced out of the heart, while diastolic pressure is the pressure exerted when the heart is relaxed.
    • Gravity affects blood pressure via hydrostatic forces (for example, during standing) and valves in veins, breathing, and pumping from contraction of skeletal muscles also influence blood pressure in veins.
  • Operation of Semilunar Valves

    • When the atrioventricular valves are open, the semi lunar valves are shut and blood is forced into the ventricles.
    • When the atrioventricular valves shut, the semilunar valves open, forcing blood into the aorta and pulmonary artery.
    • When ventricular systole ends, pressure in the left ventricle drops rapidly, and the aortic pressure forces the aortic valve to close.
    • When ventricular systole ends, pressure in the right ventricle drops rapidly, and the pressure in the pulmonary artery forces the pulmonary valve to close.
  • Defecation Reflex

    • Defecation is a combination of voluntary and involuntary processes with enough force to remove waste material from the digestive system.
    • In the adult human, the process of defecation is normally a combination of both voluntary and involuntary processes with enough force to remove waste material from the digestive system.
    • The rectum now contracts and shortens in peristaltic waves, thus forcing fecal material out of the rectum and out through the anal canal.
  • Interactions of Skeletal Muscles

    • The largest motor units have as much as 50 times the contractile strength as the smaller ones; thus, as more and larger motor units are activated, the force of muscle contraction becomes progressively stronger.
    • A concept known as the size principle allows for a gradation of muscle force during weak contraction to occur in small steps, which become progressively larger as greater amounts of force are required.
    • For skeletal muscles, the force exerted by the muscle can be controlled by varying the frequency at which action potentials are sent to muscle fibers.
    • In a typical circumstance, when a human is exerting as much muscular force as they are consciously able, roughly one-third of the fibers in that muscle will be contracting at once.
  • Capillary Dynamics

    • The movement of materials across the capillary wall is dependent on pressure and is bi-directional depending on the net filtration pressure derived from the four Starling forces which modulate capillary dynamics.
    • There are four forces, termed Starling forces, which modulate capillary dynamics.
    • Hydrostatic pressure is the force generated by the pressure of fluid within or outside of capillary on the capillary wall.
    • The net filtration pressure derived from the sum of the four forces described above determines the fluid flow into or out of the capillary.
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