KIN 3514 - work, power, and energy

what is work?

the product of force and the amount of distance in the direction of that force; performed if the object is linearly displaced by the force application

what is the formula for work?

𝑊 = 𝐹(𝑑)

what is positive work?

Work is done on an object; Applied force on the object is in the same direction as the displacement of   the object

what is negative work?

Work is done by an object; Applied force is in the opposite direction to the displacement

true or false: No matter how much physical effort was involved on the part of the person, technically no mechanical work was performed if the object wasn’t displaced

true

what does the first image show?

zero work; Physiologically, the lifer did some work, but mechanically, zero work was done on the barbell .

what does the second image show?

negative work; Mechanical work is negative if the force acting on an object is in the opposite direction of the motion(displacement) of the object.

what does the third image show?

positive work; Mechanical work is positive if the force acting on an object is in the same direction of the motion(displacement) of the object.

How much work did the lifter do on the barbell from the start until the finish of the lift?

none; there is physiological work, but no mechanical work

what is isometric contraction?

The muscle remains the same length; No displacement of muscles’ insertions in relation to each other; No work is performed

what is concentric contraction?

The muscle shortens as it contracts; Muscle force acts along the line of muscles’ insertions; Positive work is performed

what is eccentric contraction?

the muscle lengthens as it contracts; Muscle force acts against the direction of the motion of muscles’ insertion; Negative work is performed

true or false: For work to be done on the object, the object must move

true

what are the forms of mechanical energy?

kinetic and potential energy

what is potential energy?

stored energy due to position or deformation

what is Gravitational Potential Energy?

the energy stored due to an object’s position above the ground

what is strain energy?

the energy stored due to the deformation of the object

what is kinetic energy?

energy due to motion; the energy stored in a moving object

what is the formula for kinetic energy?

KE = 1/2*mv²

what are the units for kinetic energy?

kg· 𝑚²/𝑠² or a joule (J)

what is the formula for gravitational potential energy?

PE = mgh

what is the formula for strain potential energy?

SE = 1/2*𝑘Δ𝑥²

what is the unit for potential energy?

joules (J)

true or false: The greater the deformation of the object, the greater the strain energy stored in the object

true

what is the formula for net work?

𝑤_𝑛𝑒𝑡  = Δ𝐾𝐸

true or false: Net work done by the external forces on a system is equal to the change of kinetic energy

true

what is the conservation of mechanical energy?

Energy cannot be destroyed, but only   transferred from one form to another   form; In the absence of externally applied force other than gravity, the total mechanical   energy (sum of KE and PE) of a system remains constant; The total energy of an isolated system   does not change

what is power?

the rate of doing work, or how much work is done in a specific amount   of time - refers to how fast work is done upon an object

what is the formula for power?

power = work/time; power = (force*displacement)/time

what is the formula for velocity?

velocity = displacement/time

what is the unit for power?

watts; 1 watt = 1 joule per second, J/s