Work

1
Work Power
2
W F d
Work Newton Meters
Work Joules
3
Caution!
Normal Force

• The force must be in the same direction as the
  distance moved or no work is done on the object.

Since the force and distance moved are not in the
same direction, no work is done on the tray!
Distance
Force (weight)
4
Effort vs Work
5
Have you done work on anything recently?
Work
I pushed a grocery cart
How do you know you did work?
How do you know you did work?
Distance
Force
Distance
Force
I pushed horizontally
The cart moved horizontally
6
Is work being done on the burrito?
Yes! W Fd W (7 N)(1 m) W 7 J
1 m
7
Is work being done on the egg?
Normal Force
Distance
No work is done on the egg
8
Is work being done?
(On the wall)
9
on the wall.
10
Power is the rate at which work is done.
P W / t
Power Joules / seconds
Power Watts
11
How Powerful is she?

• When doing a chin-up, Courtney lifts her
• 425 N body a distance of 0.25 meters in 2
  seconds. What is the power delivered by her
  biceps?

12
Work Power Calculation Practice
13
What is the work done by Hajji who lifts a 30 kg
bag straight up 1.5 meters? If it takes 0.5
seconds, what was his power rating?
W ? m 30 kg d 1.5 m t 0.5 s P ?
W Fd
Fw mg Fw (30kg)(9.8 m/s2) Fw 294 N
W (294 N)(1.5 m) W 441 Nm or J
P W/t P 441 J / 0.5 s P 882 J/s or 882
Watts
14
How much time did it take for Marx to lift a 10
kg object 4 meters if his power rating was 160
Watts?
15
POWER LAB
16
Work
The work done is W F d force x
distance
weight x height (mg)(h)
17
Where to?
4th floor
Group 7
Group 5
Group 6
3rd floor
Group 4
Group 3
2nd floor
Group 2
Group 1
1st floor
18
Where to?

• Group 1 Stairs from 1st floor to middle 1st and
  2nd
• Group 2 Stairs from middle of 1st and 2nd to 2nd
  floor
• Group 3 Stairs from 2nd floor to middle of 2nd
  3rd
• Group 4 Stairs from middle of 2nd 3rd to 3rd
  floor
• Group 5 Stairs from 3rd floor to middle of 3rd
  and 4th
• Group 6 Same as group 5
• Group 7 Stairs from middle of 3rd and 4th to 4th
  floor

19
Work, Power, Energy ? Hockey

• http//www.nbclearn.com/portal/site/learn/science-
  of-nhl-hockey

20
Simple machines can be used to change the
direction of force
Work Force x Distance Work 30 N x 4 m Work
120 Nm or 120 J So the horse has done 120 J of
work ON the bucket
30 N
Bucket goes up a distance of 4 m
Buckets weight
30 N
21
Images Cited

• http//a.abcnews.com/images/WN/pd_scream_071012_ms
  .jpg
• http//xpigs.files.wordpress.com/2007/12/latest-de
  sign-waiter-waitress-trays.gif
• http//www.celticstrongman.co.uk/weightlifter_barb
  ell_squats_hg_wht.gif