ShmoopTube

00:03

Work and power still physics stuff not how to become a

00:07

supervillain.......

00:17

okay you people welcome to my lair of [Man welcomes people to his lair]

00:20

doom come on every good supervillain has a lair no one takes you seriously if

00:26

you're holding the world for ransom in your dining room and every good

00:30

supervillain has something else power the power to make people do whatever you

00:35

want them to do most the time I just want someone to get me a milkshake but [Supervillain talking and minion appears]

00:38

you know still it takes power to do that now physicists will tell you that making

00:43

someone get you a delicious cold vanilla treat with Oreo bits blended.....

00:48

....According to physics, power is something

00:52

completely different in fact power is related to work now

00:56

I'll be honest work isn't exactly my favorite thing I'm a pretty lazy [Supervillain laying in a hammock]

01:00

supervillain I'm in the Union here but power and work means very specific

01:05

things when it comes to physics so what is work well let's talk about what it

01:10

isn't first of all let's say my wife and I go to the mall to do a little [Villain and wife at the mall]

01:13

supervillain shopping well that's the nice thing about this profession

01:17

you know get to set your own hours she picks out a bunch of things to try on

01:21

and ask me to hold her purse which is cool I'm a modern supervillain totally [Man holding wifes purse]

01:26

comfortable with my masculinity but honestly this thing weighs a ton what

01:30

does she carry in here gold bars well after 10 minutes my shoulder is aching

01:34

when she comes back with her selections I tell her how much work it was holding

01:38

this dead weight but since she's all scientific she's happy to tell me that I [Wife appears with lots of clothes]

01:43

did no work at all why because I just stood there not moving just a man

01:48

wearing a man bag see work in the physics dictionary requires movement to

01:54

put it precisely work as a force being applied which causes an object to move a

01:58

distance in the direction of that force in fact that's the whole equation really

02:02

work equals force times distance and it's important to point out that while [Work equation example]

02:08

forces of vector quantity work is a scalar

02:11

quantity since work is all about force applied over distance and that distance [Woman pushing a box]

02:15

is in the direction of that force we don't have to include another

02:19

directional component to work the direction is already baked into the cake

02:23

so to speak mmm cake right so force is measured in Newtons as always and

02:28

distance is measured in good old meters and it's important to really understand

02:33

that whole in the direction of force thing... Yoda knows what I'm talking about [Yoda appears]

02:37

imagine you've got your hand open with a book resting on it or don't imagine it

02:42

go grab a book and let's do some real science if you raise your hand up the

02:46

book moves upward you're applying an upward force the movement is in the [Book floating]

02:49

direction of that force and what do you know you're doing work on the book well

02:53

the work is coming directly from your arm/hand but in the same scenario

02:59

what happens when you move the book from left to right is your hand still doing [Supervillain moves book left and right]

03:03

work on the book well let's ask another question if friction stopped existing

03:08

while you were waving this book around in the air would the book stay in your

03:12

hand no your hand would slide right under it the book would fall down and [book falls to the floor]

03:17

gravity would work its way right down on your big toe when the books resting on

03:22

your palm and you're moving it laterally the force that's being applied actually

03:26

comes from friction so the chemical energy from your body isn't creating the

03:31

force that's working on the book the work is coming from friction well that

03:37

can be a little tricky to understand even from a super genius supervillain

03:40

like me so take your time to understand it go on hit the pause button and wave a [Minions waving books in a room]

03:43

book around I don't mind alright we'll work is the transfer of energy from one

03:47

place to another when you lift your cat off the ground you're taking chemical [Supervillain picks up a cat]

03:53

energy from your body and changing it into gravitational potential energy and

03:57

when that cat wiggles free and drops to the ground while gravity works on the

04:01

ungrateful feline changing the potential energy into kinetic energy, because of

04:07

this relationship to energy work is measured using the same units as energy

04:11

joules.. now let's talk about my favorite subject power but we're talking about

04:17

boring old physics power not fun exciting world domination [Supervillain discussing power]

04:20

- in terms of physics power is the rate at which work is done just as speed is

04:26

measured in miles per hour - power is measured in work per second.. here's the

04:31

equation for it power equals work divided by time and you might be saying

04:35

to yourself what is the unit for power and you'd be absolutely correct okay

04:41

not as in WHAT but a WATT... supervillains can crack jokes were not

04:47

always uptight psychopaths bent on destruction with an eyepatch

04:51

a watt equals one joule per second and it's a measure of energy transfer so if [example of 1 watt equivalent to 1 joule of energy]

04:56

you have a light bulb that's labeled 30 watts well that means every second that

05:01

light bulb is turned on it's converting 30 joules of electrical energy into [light bulb turns on]

05:06

light energy and heat well that can add up if you leave the lights on all day

05:10

but there's probably a lot of stuff in your house that uses way more power your

05:15

microwave might use 700 watts or it might use way more... Your hairdryer

05:21

well like chances are that thing uses over 1500 watts that's why I let my hair [Girl blow-drying her hair]

05:27

air dry I may be evil but I'm still environmentally conscious okay so I'm in

05:32

my lair of doom trying to figure out what to watch on Netflix when one of my

05:37

hench women comes in wheeling the evening cheese cart yeah when you're a [hench woman wheels in cheese cart]

05:42

supervillain you can just tell people to bring you a cart full of cheese this

05:46

line of works looking better and better huh when henchy here pushes the cart

05:50

some of the force pushes down and some of it pushes horizontally in the

05:55

direction of motion in fact my sensors detect that the vertical component of

06:00

the force equals 30 Newtons and the horizontal force is 40 Newtons if she [horizontal and vertical force of the cheese cart appears]

06:06

pushes the cart for 20 meters along a flat surface how much work is done? well

06:11

look among the potential jobs you could have working for a guy like me cheese

06:15

cart pushers a pretty sweet gig but there's definitely work involved let's

06:19

do a little diagram for this setup we've got a distance 20 meters and two amounts

06:23

of force F sub y which is 30 Newtons and F sub X which is 40 Newtons and of

06:28

course we've got our work formula which equals force times distance

06:32

which force do we use though do we add them together get an

06:36

average flip a coin well the crucial factor here is that work is a force [Supervillain flips a coin and work definition appears]

06:40

applied over a distance in the direction of motion our motion is along the x axis

06:45

so that's the force we'll use to find the work we just have to multiply the

06:50

distance times that force which gives us an answer of 800 joules

06:55

well this cheese is delicious keep up the gouda work there Tim....Let's

06:59

go back to light bulb if a 30 watt light bulb is turned on for seven minutes how [Light bulb turned on swinging side to side]

07:03

much energy does it use well wattage is a measure of power which is a measure of

07:07

work per second and work is all about force and distance right but wait I'm

07:12

just flipping a light switch there's not a lot of distance involved in that how [Supervillain switches light switch on and off]

07:16

does this work well electricity moves through circuits and it involves voltage

07:22

and ampules and really we'll get into all that stuff later the important thing

07:26

here is that electricity is zipping through all sorts of wires to get up to

07:30

the light bulb so work is definitely being done even if you don't directly

07:34

see it we've got our power 30 watts and we've got our time seven minutes but

07:40

that little T in our power equation means seconds not minutes so let's [Supervillain discussing power equation]

07:46

multiply that seven minutes by 60 seconds giving us a T value of 420

07:50

seconds now we can multiply each side of the equation by 420 seconds to solve for

07:54

W and when we do that we find that the work equals 12,600

07:59

joules okay it's time to put my evil scheme into action I'm gonna drive out [Supervillain appears outside with minions]

08:04

to the airfield to initiate phase one I'll hop in my electric car and crank it

08:08

up when the cars going thirty meters a second I'll put it in cruise control [Car driving by in cruise control]

08:11

well the engine produces 2,000 Newton's of force how much work is done by the

08:18

engine over a distance of 50 meters and how many watts is the car engine

08:23

expending okay let's figure out what we have here first we've got a force we've

08:28

got a velocity and we've got a distance we want to find work and power...well, work

08:33

should be pretty easy that's force times distance and we've got both of those [force and distance circled]

08:37

right there so let's solve that one real quick the cars work equals 2,000

08:41

Newton's times 50 meters giving us a total of a 100,000 joules thank

08:45

you Tesla...now for the power well that's just

08:48

work / time wait do we have time I don't recall seeing time in our list of

08:54

variables but we do have velocity and we also have a distance so going all the

08:58

way back to the beginning of our physics learning, we had a nice little [Person travelling quickly down a road]

09:01

equation for speed while speed equals distance divided by time but before we

09:07

plug in any numbers we need to do a little presto change-o and rearrange [Supervillain transforms into a magician]

09:11

this equation to solve for time we'll multiply both sides by T then divide

09:14

both sides by S so time equals distance divided by speed and we can get all

09:18

numerical here on you.... 50 meters divided by 30 meters per

09:22

second gives us a time of 1.67 seconds now we can figure out my favorite

09:27

variable sweet-sweet power our work is still a 100,000 joules and we

09:31

divide that by 1.67 seconds giving us a power of 60,000

09:35

watts.. oh that's a lot of the good stuff right here power and work can be a [Car drives by a rocket launch pad]

09:40

little tricky to understand first after all as you sit here processing all this

09:43

physics stuff you might feel a little worn out which makes sense...Learning [Girl falls asleep while studying]

09:47

these concepts can be hard work except according to physics you're not doing

09:51

any work at all sitting motionless may be tiring but that doesn't mean any work

09:55

has been done people and no work means no power even if you spent years

10:00

thinking about physics figuring out how Einstein was a schmuck who got it all

10:04

wrong all that time will still equal zero [Man transforming facial features]

10:07

power....Power is work over time but just in case your mom and dad goes to an

10:13

office and sits in front of a computer all day well don't tell them they didn't [Dad walks in to living room from work]

10:17

do any work might not go over so well...

Full Transcript