Worksheet #9: Work, energy, and power

Work: unit of measurement

Joule (J)

linear work

product of force applied to an object and its displacement

linear work: formula

W = F x d

angular work

product of torque applied on an object and its angular displacement

angular work: formula

W = T x θ

positive work

force/torque and object's displacement are in the same direction

positive work: muscles

concentric (shortening) muscle contraction

negative work

force/torque and object's displacement are in the opposite direction

negative work: muscles

eccentric (lengthening) muscle

kinetic energy

energy possessed by a moving object

kinetic energy: equation

KE=1/2mv^2

factors that affect kinetic energy

mass (kg) and velocity (m/s^2) on the object

gravitational potential energy

energy an object possesses due to its height

gravitational potential energy: equation

GPE=mgh

factors that affect gravitational potential energy

mass (kg) and height (m) of the object

strain energy

potential energy an object possesses due to deformation

strain energy: equation

SE=1/2kx^2

factors that affect strain energy

stiffness of structure (N/m) and the deformation (m) caused

total mechanical energy

energy the object possesses due to motion or position in space

(always a positive number)

total mechanical energy: equation

E = KE + PE

factors that affect total mechanical energy

motion or position of object in space

law of conservation of mechanical energy

when gravity is the only external force acting on the object, the total mechanical energy of the object remains constant

Kinetic energy increases

A (because they are running fast)

strain energy increases

B (energy is stored in the pole because it bends/deformed)

gravitational potential energy increases

C (the height of the the individual and the pole increases)

kinetic energy increases

D (the individual is falling, its velocity increases)

Type of potential energy

gravitational potential energy and strain energy

energy

something an object "has"

(The ability to do work or cause change)

the more energy=

the more capacity to produce work

Work-Energy Relationship

work produced on an object is equal to the change in mechanical energy of the object

positive work...

increases the object's mechanical energy.

work is done to transfer mechanical energy to the other object.

negative work...

decreases the object's mechanical energy

work is done to absorb the other object's mechanical energy

calculating force in mechanical energy/work

F = Δ total mechanical energy / d

mechanical power

rate at which mechanical work is being produced

mechanical power: unit of measurement

J/s or Watt (W)

mechanical power: formula

power = F x d/t

power is + when the work is...

+ and the muscle is contracting concentrically

power is - when the work is...

- and the muscle is contracting eccentrically

the area under power curve

represents the work produced (and the mechanical energy transferred)

increase the average force needed to lift the barbell based on the work-energy relationship

lifting barbell higher, adding more weights to the barbell, moving the barbell up quicker

decrease the average ground reaction force applied to the gymnast during landing

greater displacement of the body's COM during landing

ascending in bench press: shoulder joint motion

+ horizontal adduction

descending in the bench press: shoulder joint motion

+ horizontal adduction

bench press ascending: sign of shoulder joint motion

+ horizontal adduction

bench press ascending: sign of shoulder joint torque produced by pec major

+ horizontal adduction

bench press ascending: muscle contraction

concentric

bench press pause at top: sign of shoulder joint motion

0

bench press pause at top: sign of shoulder joint torque produced by pec major

+ horizontal adduction

bench press pause at top: muscle contraction produced

isometric

bench press descending: sign of shoulder joint motion

- horizontal abduction

bench press descending: sign of shoulder joint torque

+ horizontal adduction

bench press descending: muscle contraction

eccentric

squat ascending: sign of knee joint motion

+ extension

squat ascending: sign of knee joint torque produced by quadriceps

+ extension

squat ascending: muscle contraction

concentric

squat brief pause: sign of knee joint motion and torque produced by quadriceps

0

squat brief pause: muscle contraction

isometric

squat descending: sign of knee joint motion

- flexion

squat descending: sign of knee joint torque produced by quads

+ extension

squat descending: muscle contraction from quads

eccentric