PK5: CH4 Work, Power, and Energy

Work

force applied against a resistance , multiplied by the displacement of the resistance in the direction of the force

EQ: W=FD

What units is work in?

newton x meter or 1 joule

True or False: work can be positive and/or negative

true

What is positive work?

(+) object is displaced in the same direction as the force

ex: pitcher throwing a baseball or weightlifter raising a bar

What is an equivalent term for anatomical positive work?

Concentric Contraction (+)

Negative work force

(-) when the object is displaced in the direction opposite of the force acting upon it

ex: weightlifter lowering the bar

What’s an equivalent term for anatomical negative work?

eccentric contraction (-)

What requires more caloric expenditure, positive or negative work?

Positive because you usually are working against gravity ie: lifting a bar above you

What is a term/ contractions that produces 0 mechanical work?

Isometric contractions because the length of muscle is unchanged = no displacement

ex: putting enough weight on a bar to hold but not to curl

Power

how quickly or slowly work is done

Power Equation

P=W/Dt or P=FV

What unit is used in Power

Watts (W) or Joule/sec

True or False: In athletics it is more important to have “weight-room” strength over power output

false, power output is more important because if you can squat a lot but cannot use that on the field it is pointless.

If you increase muscle contraction velocity, what happens to the force?

It decreases, slow contractions produce more force.

Power Equation

P=FV

When is it peak for an athlete to find their max power output? And when is the max output?

it occurs at a velocity that is ½ that muscle max contraction velocity

the max output is right in between the longest and shortest

True or False: Max output goes down when duration goes up

True

ex: sprinters use high power for short periods of time

Energy

capacity or ability to do work

What are the two types of energy ?

kinetic: energy in motion

Potential: energy due to position (stored energy)

Kinetic Energy Equation

KE=1/2mv*2

Does mass have anything to do with kinetic energy?

heavier objects ave more kinetic energy

What are the 2 types of potential energy’s?

1. gravitational - due to objects position to earth

   1. PE=mgh. g=9.81

2. strain or elastic - energy due to the deformation of an object

   1. SE=1/2kx*2

   2. x = distance

   3. k = stainless or spring of material

True or False: suffer objects have a greater strain energy when deformed

True, they do have greater strain energy when deformed because it was harder to do

When objects are the max apex, height, and PE what are the values of velocity and KE?

Zero and as something falls it gains KE and velocity, while losing PE

Law of Conservation. of Mechanical Energy

when gravity is the only acting external force, a body’s mechanical energy remains constant

Constant = (PE+KE)

Are work and energy released?

yes, directly related because work done by an external force (outside of g) causes a change in energy of the object

What work do you have to do to increase energy?

• change velocity which changed KE which increase work

what Work do you need to do to Decease energy?

catching a ball reduced the balls KE?