Power - Physics 101 / AP Physics 1 Review with Dianna Cowern

Lesson 11 (Power) of Dianna's Intro Physics Class on Physics Girl. Never taken physics before? Want to learn the basics of physics? Need an AP Physics 1 review before the exam? This course is for you!
Exercises in this video:
1A) You carry a 1kg backpack up a 6m hill. How much work did you do?
1B) It took you 60 seconds to walk up that 6m hill. What average power did you exert carrying up the backpack?
1C) You ran faster up the hill a second time. It only took you 30 seconds. What average power did you exert over this time, to move the pack?
1D) The energy required to move the pack is the same in both cases. Why are you more tired after the second, faster run?
2. How many Joules are in a kWh?
3.On a given day, 2800 cubic meters of water fall over Niagara falls every second. If that water falls 50m, what is the average power of the water splashing onto the rocks below?
4. For reasons, you are hauling yourself up with a rope attached to a platform you’re standing on. The rope goes over a pulley attached to a tree, and back into your hauling hands. Your total mass (you+platform) is 100kg. You are hauling yourself up at a rate of 4 m/s. How much power are you exerting?
Special thanks to Allen Pan for his awesome shoutout at the end of the video! Check out his channel ‪@allenpan‬
Credits:
Dianna Cowern - Executive Producer/Host/Writer
Jeff Brock - Lead Writer/Course Designer
Laura Chernikoff - Producer
Kailtyn Ali - Video Editor
Sophia Chen - Researcher/Writer
Erika K. Carlson - Researcher/Writer
Hope Butner - Production Assistant
Levi Butner - Videographer
Lauren Ivy - Set Design
Vanessa Hill - Consulting Producer
Aleeza McCant - Illustrator
Rachel Allen - Illustrator
Consultant - Kyle Kitzmiller
Lucy Brock, Samantha Ward - Curriculum Consultants
Cathy Cowern - Transcription

[@TiagoFreire]

- You are so radiant today! - Every day , actually, about a hundred watts.

[@safihalim_1]

In order to keep it simple, the power in the first case can be calculated as force applied by her × velocity at which she is pulling the rope (the relative velocity) So it's 500N × 8m/s = 4000W !!

[@elizabethcastreje7801]

I am an applied physics major, and I love your videos! I have been watching for a long time, but this is the first episode of this im watching and it brightened up my day thank you!

[@mehmetsk3170]

I don't understand anything

[@seanmcdermott2035]

"And now the joke is even more funny because I explained it" lol My friends would definitely agree

[@RockyTremblay]

When discussing gravitational potential energy, might consider using GPE instead of PE. Another great lesson. Thank you ‘Physics Girl’.

[@andriyaa6029]

I am a middle school student, and my dream is to become an Astrophysicist, and only yesterday, I was talking to my parents like "I am no good at Physics. Physics is boring and I can't understand anything." After watching hundreds of your awesome and cool videos, I find it sooooo interesting!! You’re so pear-fect at Physics and fun and Thanks a ton! I really ap-peach-iate it !!!

[@jerrybyers2172]

Having a great teacher makes all the difference in the world!

[@TheHuesSciTech]

19:00 If Gwen is pulling down with her arms only, she'd be taking up 8 meters of rope per second when the lift is going up at 4 metres per second. So you get 500N of tension in the rope * 8 m/s = 4000W. I'd argue that's a more intuitive correction to the formula?

[@hitoshiyamauchi]

I would like to agree with @TheHue's SciTech. It's the person's power. Diana's answer is the platform's power, so, I would say both correct and depends on how to see this problem. My personal preference is Guinevera does the work. If the platform has a motor to pull the rope, 500N * 8 m/s. But if we don't care about the internal model, then I would like to go to the potential energy way. This looks more like a movable pulley problem instead of the fixed pully problem.

[@francissirizzotti7283]

I always liked the kWh unit, because I think it aligns really nicely with the integral you're paying for. For me, learning to express it as "For some period p, your energy usage is the integral from t_0 to t_0 + p, of some function f(t) - which measures your instantaneous power expenditure" really helped nail down my conception of the power grid and how it works. Maybe that's a bit of a backwards conception.

[@johnspisak9729]

Always awesome and fascinating and entertaining and so smart.

[@nishthasharma22]

Thanks a bunch for these wonderful videos, Diana!

[@PappaLitto]

The hill's height in the same, but the distance to 6m is further in the shallower hill in your example. You technically have to go further in the shallow hill thus requiring more energy. You also can go slow up the steep hill, taking 60 seconds as well, requiring potentially less energy than the shallow hill because the distance is less.

[@TonyRule]

Another way to think of the spring is that it's just a straight torsion bar that's been coiled. By cutting it in half, the angle you can twist it with the same applied torque is half, so the spring rate (k) has doubled.

[@rey6095]

i love your channel so, so much!! i never knew i liked science/ physics, but after i saw your videos, IM LITERALLY ONLY WATCHING THIS ❤️❤️

[@MrKen59]

I feel so powerful 😷. I’ve often wanted to calculate the amount of energy is lost when a poorly timed traffic light causes a bunch of vehicles to decelerate from speed, then accelerate back to speed vs. working to keep them rolling. Seems a smart light can make a huge difference in power/energy use. Thanks Diana and team.

[@NiHaoMike64]

If the timing is predictable, you can beat the system by driving slower, so your average speed is actually higher.

[@MrKen59]

@@NiHaoMike64 I agree, but most won’t do that. How many times have you sat at a traffic light with no oncoming traffic, then when the light finally changes, it happens when a pack of vehicles are approaching. We are building cars now that turn the motors off when idle more than a few seconds, but why not use all the knowledge we have and the ability the land a booster unattended on small dot to make traffic lights smart? This is something that bugs me so much. This does not sound like a hard problem, plus let’s remember that remember energy is not free. Stopping an 80,000 lb truck from 45mph for a traffic light that is clueless as to why, then accelerating that same vehicle takes energy. This is why I appreciate these lessons on physics, because it encourages us to think

[@NiHaoMike64]

@@MrKen59 In some parts of China, they did it in a much lower tech way: countdown displays to tell how long the red or green light will last.

[@MrKen59]

@@NiHaoMike64 We have it here as well as the walkway counters can give you an indication of the change - however if you have cars waiting on a light and no oncoming traffic - let them go. There is an intersection in Breezewood PA that will hold you for several minutes because of a poorly designed major intersection. They are not timed for current traffic, but heavy load, and it makes no sense at all. All I'm saying is we need to use our brains, look at energy beyond MPG ratings. We can be smart about how we use energy and so the simple things first. One traffic light can effect thousands of vehicles hourly, including all sizes , makes and age which makes this a better solution than forcing automakers to do the impossible.

[@samedwards6683]

Thanks so much for creating and sharing this educational and entertaining video. Great job. Hope that each day you are feeling better than the day before.🙏

[@Sohamsta]

It’s 23:35 but this video is more interesting than sleep

[@Crosley1933]

A am currently taking a physics class and these videos are extremely helpful! Thank you!

[@Dppel_6nger]

You are perfect and no one can replace you . I love it .

[@michaelcornish2299]

I like the the last problem you did highlighting a common mistake. I always do energy first when I teach mechanics as it is often the easiest way to solve problems. It also lifted things a little :)...

[@cosmos_arjun]

Awesome video Diana. Very informative helped me a lot. Want you to keep making videos like this all the time.

[@SonuSharma-hb1ox]

Your videos are Enjoyable just like professor Walter Lewis I watch his every single video of physics he is also teach concepts just like you makes enjoyable and loving❤️ thanks😊 keep going u r doing a great job💯 love ur 🎥🥰

[@efugee]

The funny thing, is when you listed the amount of people's wattage to equal the sun, their combined mass and gravity would collapse and actually become a new star.

[@NewMessage]

That guy must have had the most infuriating conversations. "Hello, there... and what's your name?" "Watt." "I say, what's your name?" "Yes... exactly." "Wait... What?" "You got it." * pinches bridge of his nose * "For the love of.... Look. Just tell me your name, man." "Watt's my name." "That's what I'm asking!!!!!!" and so on...

[@riseandshinemrfriman5925]

"Dude, what does mine say...Sweet, what about mine? Dude, what does MINE say? Sweet! What about mine??" "DEEEEEWD'UH" WHAT.DOES.MINE.SAY.....SUUUUWEEETuH...."

[@sandybarnes887]

Who's on first?

[@MikeB12800]

Who, Watts on second

[@FlyingSavannahs]

"...Yes, Watt's my name!" "FOR THE LOVE OF NEWTON!!!" "Third Law!"

[@nzjacob]

I have a friend who has the surname "Watt" .. and when he joined the police force he had almost this conversation on day 1

[@timjohnson979]

Dianna, love your videos, but you said something in this video just after time 10:45 that water could generate storable, usable energy. But, generated electricity from a power plant normally has to be consumed right away. Sure, it could be used to charge a battery, or pump water to a high reservoir, but that's not what power generation is usually about. Usually, it's consumed immediately. Power plants are constantly balancing generation and consumption (load balancing).

[@matt_the_musician]

Wow, this is amazing and fascinating! 😀👍🏻 Very well done!

[@TristanJCumpole]

I always liked the mental exercise of visualising how much liquid fuel a car uses to travel between two points as a sort of "The Abyss" alien tube. This stretches between the points of travel and has a volume (three dimensional) equal to that of the fuel used. The two-dimensional cross-section tube varies constantly between A and B corresponding to the instantaneous representation of fuel demand ("usage" seems inappropriate as that requires the third dimension time, which makes this a three-dimensional value). I guess that a tube whose cross-section perpendicular to time is always cylindrical could be appreciated as two-dimensional, using the example of a single-fuel car (ignoring oxygen). This is a rabbit hole.

[@GooogleGoglee]

Diana. Just to let you know there is a problem in the spring questuon... If you can the spring in half the spring still keep the same constant but if you stretch it twice the length then obviously as for the first it will pull back with 2 times the strength

[@stefane2952]

5:15 Actually, 58 watt is only enough to lift 1kg 5.8 meters in the air per second.. it takes 10 watt per meter

[@sanzidatasminali6992]

Yeah, I stopped when Dianna said 58 m as the acceleration due to gravity, roughly 10 m/s^2, gets factored in to give 5.8 m, which is the height the 1 kg book would reach in 1 s

[@robertabell9182]

You really help me understand math 🧮. Thank you 🙏 please keep up the great 👍 work. Merry Christmas and happy New Year 🎆.

[@iabervon]

I think the main reason that electricity bills are in kWh is that people have a better idea of the amount of time that their devices were on in a billing cycle in hours than seconds. People just have a lot of trouble thinking about times in seconds over a couple hundred, even if they use metric units in general. On the other hand, people are more likely to measure a device's power over a second than an hour. You end up with an "attention spans per part of a billing cycle" conversion in there to be convenient for both.

[@auradelluca9832]

My goodness you're so kind and your explanation is so damm clear!!!

[@TristanJCumpole]

"Instantaneous power" is often a term misused by say, appliance manufacturers to generate "power" specifications for products that don't actually have useful meaning. I may be slightly off track here, but that is when the system is doing no useful work, or is stalled? Either state is not really describing a useful aspect of a product that is meant to be doing important things between those two states! I'm hoping a commenter can refine my blunt description. edit: 9:50 oh cool

[@herambpatilofficial]

You are nailing every physics topic!!!! Thanks for such a great videos! By the way, will you make videos on topics like Electrostatics and magnetism and electricity?? Thanks again...

[@thomasewing2656]

Don't forget ghosts and Bigfoot!

[@itsdeonlol]

Simply great Diana!

[@pacmonkruz9846]

I don’t like the math , because I don’t know it ..... but the ways you explain it , it’s brain food that I’m sure my son will need , ty

[@charles_wipman]

The APAT tank shells also generate plasma as armor piercing thing; anyway, at the begining of the video when i'd seen those solar plants that made me think in the last Michael Moore documentry, 'Planet Of The Humans' that can be seen for free here on YT, that documentry did left me very worried about the efficiency of our "green" energy sources and i was wondering if you could adress some of that, as scientist, in future videos.

[@matthewrussell9760]

I drive by that solar power plant every week! Its really neat to notice how different it looks every time

[@hosseinrafie5708]

finally a good physics lesson... thanks Dianna ❤️

[@FlyingSavannahs]

Finally?

[@hosseinrafie5708]

@@FlyingSavannahs bad teacher... boring lessons... but this one is different

[@FlyingSavannahs]

@@hosseinrafie5708 Got it! Yep, I like her approach.

[@usnaveen]

Love your shows. Keep it coming. Love from india 😊

[@bernardobritto8352]

Just amazing! Love this series

[@Mouse_007]

in the steep hill / shallow hill explaination : What is the g in your equation mgh (change of potential energy) where m =mass 1kg , h = height 6m what does g stand for and how did you determine it was 10 ?

[@frankgulla2335]

Thank you, Diana. You may be replacing my classic suggestion to undergraduates for learning physics, Asimov's "Understanding Physics"

[@thomasewing2656]

Diana Azimov.

[@WouterVerbruggen]

Note that the vast majority of the heat coming off a human is transferred in the form of convection. Human body (skin) temperature is very close to its environment in most cases, so the radiation heat transfer is very small. In general, radiation heat transfer is negligible in "normal" ambient conditions.

[@CorwynGC]

Most of it is in the form of phase conversion. Evaporating sweat takes a lot of energy.

[@WouterVerbruggen]

@@CorwynGC Good point, didn't think about sweat! When looking purely at the heat that gets put into your room, you shouldn't include it though. As Dianna specifically looked at the heat flow "radiating" from a human, that's the situation I considered. Instead of the total heat lost by the human.

[@CorwynGC]

@@WouterVerbruggen Well the convective heat loss isn't going to show up in a thermal picture either, so you 'shouldn't include that'. The human's 100 watts gets spread between conductive, convective, and radiative heat transfer, and phase change followed by convective heat losses, as I mentioned. There is a lot of science on what the proportions are, and where it ends up, and eventually leaves the room. The radiative heat losses are, of course, the only thing that the thermal camera can measure.

[@FlyingSavannahs]

I think it's safe to say that, at this level of instruction, Dianna means _all_ forms of energy transfer into the environment. But the relative mechanisms and measurability are interesting, nonetheless! 🧱🧱🧱🧱🧱 🧱💡〰️🥵🧱 🧱🧱🧱🧱🧱

[@WouterVerbruggen]

@@CorwynGC Very true. I'm just adding a footnote about how radiative heat transfer is so low in a standard ambient. The vast majority of people do not know that! It's so bad, the wall-mounted heat exchangers in your home are commonly called 'radiators' XD

[@ACuriousmind007]

This is what boosts me towards my dream of becoming a scientist

[@cjg8763]

How many watts did Clark Griswald use when powering his light display in Christmas Vacation? 😆😆😆

[@RomaineChutckhan]

Asking the true questions i see

[@toddboothbee1361]

Could you do a video on the difference between the persona Dianna and the more usual Dianna, and the powers of each?

[@FlyingSavannahs]

I can't believe I botched the spring constant puzzle! "Forgive me, O Goddess of the Universe of things both seen and unseen, Decider of markers worthy of catching and Freehand Drawer of circles most perfect, for I have failed you! Please accept my humble derivation of Second Order Perturbation Theory for a Particle in a Potential Well, written 50 times in ink, double spaced, on college ruled paper, as atonement for my transgression, O Revealer of Infallible Laws with possible Blessed Holy Exceptions."

[@danielhooke6115]

3:24 Actually, horse power was originally used to measure the power of steam engines, by... James Watt.

[@arincrumley]

Boils salt. Not water. I think. Molten salt. Because it keeps its heat later into the night than water would. If I am wrong then that one doesn’t work that way but some of them do.

[@CorwynGC]

*Melts* salt.

[@daveturnbull7221]

This video cost me an hour of my life so far and i haven't even finished watching it. My poor little braincell keeps going off at tangents like 'why do we describe somebody attractive as being hot?' Are they actually radiating more heat or is it that looking at them cause us to generate more heat? Guinevere is going up at 4m/s - how big are her arm muscles to be able to propel herself upwards at that sort of speed? As always Dianna makes my day brighter (but less productive) by making me sit down and consider so many things I never would have otherwise. Oh - another thought! Sell the paper covered with your examples. Genuine collectors items!

[@NiHaoMike64]

Those who eat a lot yet stay skinny are "hotter" in the sense that they radiate more. (Most famous one I'm aware of: Naomi Wu.) The energy has to go somewhere...

[@madhusudansinghshekhawat8853]

Physics girl explanation is great

[@spvc4696]

**Excuse me would you be willing to please make a video on what you consider to be the most important plus in demand careers to have today or in the future? Thumbs up to everything with the KZbin channel.**

[@MrBen527]

Great tutorial!!

[@mikehunt602]

at around min 5:20 you talk about lifting a book in seconds, did you mean hours, or is the light actually burning that hot? watts is often expressed in hours so that is why i'm curious!

[@spotlightofficial788]

Educational and entertaining. Nice.

[@osmosisjones4912]

What about jell . It's not quite liquid or solid. . And should the water on a wet hand in deep fire concidered a plasma shield

[@johnh3733]

Given that power is dependant on time does that mean power is relative? Would a person traveling at half the speed of light appear to emit a different body heat to a person at relative zero?

[@pingnick]

Just saw you on Twitter and hoping for good New Zealand news!🤯

[@butchbardin7948]

Does gravity create friction?

[@marka.desimone44]

Hey your catches are getting better....

[@sonamshrish430]

Diana, Just to let you know, tomorrow is my Chemistry final.

[@amrutha.n.s]

Best of luck

[@abiifiraa2088]

Gud luck wish u all the best

[@deepakjoshi823]

How was your exam?

[@amrutha.n.s]

How was it I hope it was good

[@localtitans4166]

How was it?

[@camilovelez8851]

I'm probably 100% wrong, but wouldn't they pulley on top of the palm tree simply redirect the force rather than multiply it by 2 given that it (the pulley) is fixed?

[@mitchellfolbe8729]

It would be a cool collaboration with one of the python teachers to turn your problems into elementary coding. Mosh, New Boston, Sentdex, etc.

[@butchbardin7948]

Ya make me wish I was younger. I'm to old to keep up with the math.

[@CorwynGC]

More power than a house... only if you ignore all the power from things other than electricity. 1.2 kW is a pretty efficient house (my efficient house was 1.27 kW in 2019) or one in Hawaii.

[@ahmedmaruf7213]

how can you use an inferred camera with the phone? I need to check this

[@mohammadshaikh3119]

please make a video on near communication technology,evolved lisa

[@nikitagusev9990]

This person (hungry - lack of energy already) who trying to get a pineapple will use more power to get this fruit than he will get later by eating it. He should watch this video before do this crazy thing and in this way he could find best solution for how to get fruit and use less energy )) Thanks for video. It is always interesting and you are great!

[@zsigmondsinventions5201]

I heard that if you eat a slice of bacon than the digestion takes more energy than the energy you get from the bacon. Is this truee?

[@mixei4]

Sure, the more bacon you eat, skinnier you become.

[@Nudnik1]

I recall celery is negative caloric food.

[@daveturnbull7221]

You forgot to take into account the amount of energy used by the big smile on your face after eating bacon...

[@CorwynGC]

@@Nudnik1 Neither one is negative caloric food.

[@anthonyguerrera191]

Can you do Physics C Electricity and Magnetism content

[@danyalbaig7635]

Hi Dianna, Please make a video on Quantum Locking ⭐

[@abhayphysics01]

Great👍

[@mikgus]

5:25 in Sweden in November it is not wasted energy! :)

[@thomasewing2656]

I was stumped by the Pineapple in the Palm Tree. Until I can sort that out, the rest of your lesson was lost on me! lol

[@Adam.Ab9898]

Dianna is Awesome

[@basaralhawi8475]

To know a bout what you don't know in something has been writen as a reason also to know what you know in something has been happen as reaction

[@jgullave16]

I really liked this video...am.in the middle of an Einstein biography now...

[@toddboothbee1361]

Can you use this to measure the power of a work of art? I bet you can.

[@DrDrunkMithu]

Guess what, . . . . My Physics Score before watching this:- 50% My Physics Score after watching this :- 100%

[@portobellomushroom5764]

That's... Not mathematically possible without extra credit.

[@peterjf7723]

@@portobellomushroom5764 It would be possible to get 100percent in an end of topic test, though I agree not so likely in a proper exam.

[@coreys2686]

The 60 watt light bulb is an incandescent bulb, not fluorescent bulb.

[@phill3986]

When talking about the energy in the Niagra Falls part, it might be better to say 1.4 GJ *each second*

[@danielquill]

@20:30 Re: the spring constant: in engineering, the modulus of elasticity of a material is a constant regardless of length - shouldn't the same apply to the spring constant?

[@FlyingSavannahs]

Start at the start with Hooke's Law, F = - kx. For the long spring measure the restoring force for a 1 cm extension. The force of the extended spring will be the same at any point along the spring since the tension of the spring must be uniform at every point. Now if you grab the halfway point to fix it and cut the far end off you have the half spring with the restoring force unchanged. But at this halfway point the long spring had only stretched half as far as its end, specifically 1/2 cm. Pull the half spring an additional 1/2 cm to match the extension used for the long spring. Since you have just doubled the 1/2 cm extension, the restoring force will be doubled. Now looking at F = -kx in both cases we have used the same extension x, so we have the ratio -F/k equal for both springs. Because the force of the half spring was two times the long spring, we see the spring constant for the half spring must also be twice as large as the long spring. Does that help answer your question?

[@danielquill]

@@FlyingSavannahs Yes, I see that now, thank you. My alarm bells rang initially because the modulus of elasticity of a material, E, is a constant and is defined as stress/strain where strain = change in length/original length - the latter ratio is the same for a given stress regardless of the length of the material. So, in the case of Hooke's law, the 'spring constant' is not really a constant as it is a function of spring length (alternatively, it is a constant as long as the spring length is not altered).

[@jgostling]

@@danielquill The way I understand it, the spring constant is a property of the spring itself, whereas the modulus of elasticity is a property of the material the spring is made of.

[@FlyingSavannahs]

@@jgostling & @Danny Quill. Good words, guys. Yep, I got tripped up on the "it's a constant of the material" mindset and chose the "doesn't change" answer for Dianna's quiz. I think calling k a "coefficient" instead of a "constant" would be much clearer, the cause of which I pledge to champion once I become a Fellow of the Royal Society. It can be useful to see the physical nature of a conventional helical spring's restoring force as the torsional force in reaction to a twisting of the linear length of the spring when straighted out into a line. A significant application of a torsional spring is the Cavendish Balance used in his measurement of the gravitational constant G. An experiment I was quite excited to do in my Junior year physics lab and ended up being the worst result, as compared to my classmates, of any of our experiments for the year. As a astronomy enthusiast, messing up on repeating the classical experimental setup for measuring the strength of the gravitational force was a real disappointment.😠 🌍➿➿➿🌛

[@konstantinkurlayev9242]

Thank you!

[@MuhammadDaudkhanTV100]

Very good

[@Conduitgene]

Wee need Th is in everyone’s rooftop

[@coco-jk2je]

can someone give me an interesting application or an example of conversion of kinetic energy to mechanical energy. not something related to rubbing hands or cycling. I would really appreciate your help. Thank you

[@Nudnik1]

Excellent

[@selvame2316]

this is in general i am asking.what would have happened if there is no concept called time

[@FlyingSavannahs]

Everything would happen all at once.

[@timeverse1545]

You are amazing , loved this video

[@WoLpH]

I wonder... is that thing safe to look at? Something that bright might be dangerous for your eyes

[@calholli]

Its actually more complicated than that... Because when the lady on the platform pulls up and hangs her body weight on the rope, it actually removes her body weight on the platform-- So she actually could never pull the full 1000kg weight on one rope.... You can't count her weight twice, and that is exactly what is happening once she applies force.

[@manojsharma8390]

You are so so cute and your voice is soooooo sweet too... 😍😍💕💕 i love you and your informative videos.. Keep doing it

[@osmmanipadmehum]

58 W is same as lifting 1kg 58 meters every second?? is it the same as a 58 kg person going up 1 meter?

[@sirwilliamkarl5591]

That plant is in California in Ivanpah dry lake.

[@Omni0404]

I love Physics Girl!

[@LukeRKU]

13:42 Great Scott!!!

[@noreaction1]

Can you make a video about dc motor design

[@bobw9297]

You are mixing up Horse shoe falls and Niagara falls , Horse shoe falls are Canadian

[@osmosisjones4912]

Could gravity be considered a form of energy

[@yoavboaz1078]

Yea, potential energy

[@maheshjayakumar569]

Do you read comments or reply to them ?