1. Power

2. Power:
Power is the rate at which work is being done [or also the
rate at which energy is consumed].
W
P =
t
E
P =
t
or
Unit : Watt (W) which is a J/s

3. A ‘Big Mac’ contains about 2,000,000 J
of chemical energy. If all this energy
could be used to power a 60 watt light
bulb, how long could it run?
Examples:
E
P =
t
E
P
t =
2,000,000 J
60 watt
=
t = 33,000
J
J/sec
t = 33,000 sec ( ~ 9 hr )

4. Calculate & compare power
• During the ascent phase of a rep of the bench
press, two lifters each exert an average
vertical force of 1000 N against a barbell
while the barbell moves 0.8 m upward
• Lifter A: 0.50 seconds
• Lifter B: 0.75 seconds

5. Calculate & compare power
Lifter A
Table of Variables
F = 1000 N
d = 0.8 m
t = 0.50 s
Lifter B
Practice by Calculating the
same was as Lifter A
w
s
J
Power
s
mN
Power
t
Fd
Power
1600
50.0
800
50.0
8.01000





6. Power on a cycle ergometer
• Work = Fd
• Force: 3kg
• Displacement: 6m /rev
• “Work” per revolution
– 3kg x 6 m = 18 kgm
• 60 rev/min
min/1080""
min/6018""
min/""
/""
kgmPower
kgmPower
revFdPower
tFdPower





7. Power on a cycle ergometer
• Work = Fd
• Force: 3kg
• Displacement: 6m /rev
• “Work” per revolution
– 3kg x 6 m = 18 kgm
• 60 rev/min
min/1080""
min/6018""
min/""
/""
kgmPower
kgmPower
revFdPower
tFdPower




1 Watt = 6.12 kgm/min

8. Compare “power” in typical stair
stepping
• Work = Fd
• Force: Push on the step
• constant setting
• Displacement
– Step Height: 5” vs 10”
• 0.127 m vs 0.254 m
• step rate
– 56.9 /min vs 28.8 /min
• Time per step
– 60s/step rate
Thesis data from Nikki Gegel
and Michelle Molnar

9. Compare “power” in typical stair
stepping
• Work = Fd
• Force: Push on the step
• constant setting
• Displacement
– Step Height: 5” vs 10”
• 0.127 m vs 0.254 m
• step rate
– 56.9 /min vs 28.8 /min
)08.2/254(.
)05.1/127(.
10
5
smFPower
smFPower
vFPower
inch
inch




10. Compare “power” in typical stair
stepping
• Work = Fd
• Force: Push on the step
• constant setting
• Displacement
– Step Height: 5” vs 10”
• 0.127 m vs 0.254 m
• step rate
– 56.9 /min vs 28.8 /min
smFPower
smFPower
vFPower
inch
inch
/122.0
/121.0
10
5



Results: VO2 similar fast/short
steps vs slow/deep steps