"It is terrible to do so but I have blocked out the sun" haha I love your videos you're awesome thanks! :)

My physics teacher is crap, so i have to teach it all to myself and this really helps, cheers man!

thank you for making physics less intimidating, i have you to thank for if i score well in my upcoming A levels :)

At 8:30 the gravitational potential energy is the work done to bring a mass m from infinity to a distance r from a mass M. That is obviously negative since PE reduces as you get closer to the mass M. But PE increases as you move away from the mass M.

what surprised me was you took the time to explain mv2/r. it was taught a long time ago to me and certainly I forgot and didn't understand this when I was watching you. Every aspect of your video revolve around the student and that is why this is so great, clear, engaging and easy to understand!

Sometimes its the tumble dryer.

if only there was a drchemistryA level

Sir you're the best! I wish there were more teachers like you.

I may not have followed the point you are making. But if you square both sides then you will indeed get an expression without the square root. But then the left hand side will be T^2. Or have I missed the point?

Washing machine in the background

Very well explained. Will check out your other vids. Thanks for uploading!

Thank you very much for this video. I honestly have learnt alot from this! Will be looking into more of your videos soon! :)

I take it you mean at 21:47 where I say r = 4.23 x 10**4 km. I haven't yet double checked it but could it be that you have calculated the value in m not km - in which case it would indeed be 4.23 x 10**7 m.

Excellent lessons. I am thrilled to have found these video lessons. Thank you. Thank you.

You can choose your own convention for signs. The one I am using assumes that potential energy becomes zero at an infinite distance away. Since potential energy increases as you go further away that means it must be negative in order to increase to 0. But as long as your signs are consistent it doesn't really matter what convention you choose.

A field doesn't do anything until you put something in. Like a temperature field that just sits there. Fields are capable of doing things, whether they do them or not. Put a block of ice in a temperature field and the ice melts. That's a brilliant start to the video! 🙌🏽🤯🔥🎊

Damn he provides a whole new perspective. Thanks sir.

Force is a vector quantity. It has magnitude and direction. The negative sign is an indication that it is an attractive force (ie the force is in the opposite direction to increasing value of r). You don't have to include the minus sign as long as you remember which way the force operates.

thank you very much i find your videos concise and extremely helpful !

Thank you for your videos. They are reviving my interest in Physics from 50 years ago when passing the exam was more important than understanding what you are doing I am a bit confused about what is the difference between Gravitational Potential Energy (about 8:05) and the more conventional mgh kg m²/s² as you mention in your Electric Field Video comparing the two (at about 11:34) Substituting values for the variables they certainly don't agree. Many Thanks.

There are so many books that I cant organise according to them all. I try to organise the videos in some logical order and hope the titles explain what they cover. I'm not sure what your Unit 4 OCR covers. Is it nuclear and particle physics? If so, there are videos on this in the A Level playlist - and more advanced videos on both in other playlists of mine.

Awesome stuff, such a huge help! I love all your videos.

Thanks so much DrPhysicsA, your videos are so helpful! :)

Thank you, your videos helped a lot! I take IB HL physics but the topics covered are nearly the same ( from the videos that I've watched) so it helps a lot.

the vedio made me understand more stuff then i understood in the class so thank u sooo much

Sunny? In the UK?!

I learned the whole topic and more in 30 min than my school teacher who teaches us for a week and i learn 0 from him. Please make more.

Good Luck on your IB physics exam tomorrow! I'm taking the same exam and I agree, these videos are indeed very helpful! Thanks DrPhysicsA! :)

you sir, deserve a medal! cheers

Wow ! The best physics teacher ever ❤️

i LOVE this, the explanation is good and easy understand.TQ so much ^^

such a wonderful explanation, thnqw

I am delighted to hear it. Well done.

This video really helped MR thanx!!

Thankyou So much SIr you explained really in great manner :)

this channel is too good

Yes, from the centre of the earth to the centre of mass of the man. But I was ignoring the extra meter or so in 6400km.

This really helps. THank you so much

Yep. Its a cuckoo clock with a cow instead of a cuckoo.

Thank you so much! these are very useful!!

if you listen very closely you can hear your brain frying

These videos are so helpful!

Great videos, thank you!

ur video is really a good tool for revision thank u :)

Hi sir woaaahh just wowwww i really love physics and you have deepen it

Love your videos!

Thank you, It was very helpful.

Fantastic videos.

Ur video rocks Very helpful

6:42 - It sounds like there's a rocket preparing to launch.

Thank u v much for the content. Just one clarification though, If the total energy = KE + PE, when the object moves to infinite distance (r=infinity) both become KE=PE=0. However when r 0, Infinity and make it equals to (mv^2)/2, then I can get the same escape velocity. But still cannot understand what happened to all PE. If somebody can help me, really appreciated. Thanks.

What is the speed falling from space to earth with a changing gravity strength. Do you do a video about this?

That's interesting... correct me if I'm wrong, professor, but considering that the centripetal force on the object is F=mv^2/r, does that not mean that the kinetic energy of a rotating body is F*r/2? That is an amazingly cool way to find that.

Amazing videos.

This was posted 10 years ago but my God you are good....

Drops lid whilst talking *oops* continues btw thanks so much for these videos, it has helped me understand mechanics a lot better than how my teacher explained it.

Sir, it would be helpful if you could tell me where I can find the video on electric fields. Its not there in your classical mechanics playlist.

WE NEED YOU PLEASE COMEBACK, IT VERY USEFULL IN PANDEMIC (2022)

Calculate the force on the 3rd due to the first and then the second using F = GMm/r^2. Since the forces will be in opposite directions the net force is one minus the other.

Thank you so much. This video is very useful for me :)

It is the mass of the earth. The mass of the satellite cancels out at an earlier stage so does not feature in the equation here. Thanks for kind comment.

Question: In the video, you say velocity, v, is a vector, but then you say it's speed at 12:32. How do you convert a vector to a single variable like that?

For escape velocity, assuming a conservative system where we end up with the kinetic and potential energy of the system as: K_f + Ep_f = K_i + Ep_i, where sub 'f' is final and sub 'i' is initial, should we not set up the equation where the left side is 0. The final kinetic energy and the potential at infinity would be zero. That leaves us with 0 = 1/2mV^2 -- GMm/r. This rids the (--) as shown in 26:31 when we rearrange to get 1/2mV^2 = GMm/r.

in my book says ' the magnitude of minimal velocity of a rocket in order for the rocket to be able to escape from grabity is = square root of 2g× m over r. is that correct ?. there was one similar except it doesnt have a square root

15:26 Moooo!

What a great teacher you are. Thank you for your videos. Could you make one describing the simple two bodies system and the equation that follows ?

Thank you so much.

I was in year 6 when this was filmed...

yh sure my teacher is a no brainer, n wif vidz lyk thez lyfz made a lot easier......................anks a lot man, u da best

great video, very clear and engaging. Thank you sir.

Do you have a video on the gravitational potential graphs etc. please?

Thanks for the derivation of T.

At 21:13- Period of geostationary, orbiting body: one sidereal day, 86,164 seconds.

Great videos! P.S. Your voice reminds me of Mark Halliley (The Apprentice Narrator).

Yes. If you think of the earth and the sun, the gravitational force from the earth to the sun is directed towards the sun whereas the distance vector from the sun is measured away from the sun. The key thing is not the minus sign but rather that you are consistent in your signing convention.

The minus sign is there as gravitational force is attractive. I get the distance in the opposite direction of the force, however that will just confuse students (why cant they measure from bottom to top etc.)

I assume you are referring to the section starting at about 11:23. You are right in all you say except "small v is the length". This is a vector diagram so v is velocity not length. See my video on adding and subtracting vectors for tail to tail subtraction of vectors. So v on both sides of the equation is velocity.

I had the same issue. If you square the whole expression, (2 x pi x r) / v, while substituting the root GM/r for the v, you get the expression you derived without the square root in the expression...

Hello sir. Very nice presentation.

Gravity is the curvature of space time. Objects are not pulled towards earth they are are essentially pushed towards earth because the earths mass bends the fabric of space around it. Most people say the suns gravity causes the earth to orbit the sun. But in reality the sun warps the space around it, which pushes earth towards the sun.

Good Day Sir, could you Show us how to calculate gravitational Potential energy at earth center?.... Thank you.... 👍👍... Very well explained Video Sir

technically gravity is just the result of the curvature of the fabric of space time and is not a pulling force. a large mass would curve or distort the space around it like rubber sheet being distorted by say a bowling ball. essentially other masses would "roll" towards the center of the distortion (like a marble rolling down the curve in the rubber sheet we talked about earlier made by the bowling ball). so gravity is not a "pull" but a "push. still like your calculations

Thanks a lot!!!

Thank you for videos, they do help me a lot. However, I am going through this video, and I seem to be confused that you have v^2 is negative for the escape velocity, also I thought that gpe+ke=0 when working out. Which might correct it?? Thanks M

thin you for this explanation,doctor,but i have a question,in this forumla ,you h'avent considered ,,,the earth mouves in orbit of the sun,this mouves infulences ,the satelite mouves ,why can you expain this in the formula,frendly

you have helped a lot over the past few weeks of revision for me. got my first A2 exam in just under an hour. I will let you know how it goes in a couple of months time. (predicted A, although will be happy with a C). Fingers crossed I guess!

Thank you sir ❤🌑

Thanks so much. :)

Hey can someone how he got the m/s^2 from the other Equation?

yo man got a B in physics, and i thought id thank you if i did cuz i swear to god i didnot know a word 3 days before the exam. i actually had to the buy the text book then cuz id lost mine, your videos saved me. thankyou very much

Two weeks before midterm Statics & Dynamics exams my British professor said that we could skip the next week's classes to study for the exam, but suggested that we show up anyway because he would "revise everything we have learned thus far". I almost passed out... in American usage 'revise' means 'change what was previously looked at', so it sounded like he was tossing out everything we had previously studied and replacing it with something else.

So helpful

Sir, your videos are awesome ! but there is something i awalys wanted to know... and i didnt found it in your channel... can you explain how the formula E= -GMm/r² come? was it determined mathematically or experimentally? Thanks !

In the first diagram you arrived at dᶱ = dx / r = vdt/r where r = radius and v is velocity In the second vector diagram You arrived at dV / v = dᶱ where dV= change in velocity and small v is the length When you equated dᶱ in both the equations dV/v = vdt/r where left hand side denominator v is length and right hand side numerator v is velocity And you have multiplied the length v lhs with velocity v rhs and arrived at v2 /r = dv/dt Could you please clarify or am I missing something. Thanks

Thanks! Unfortunately though, CIE tends to ask why there is a negative sign, and they don't accept the direction argument.

I am a little confused with the equation F = (-GM1M2)/r^2 Do the masses need to be in a certain order? As in is M1 the mass of the sun and M2 the mass of the planet for example? (As the sun is heavier than the planet). If that is correct then is that the same for the equation r1 = (m2*d)/(m1 + m2)?

ls it really necessary to put the negative sign on force

At 21:00 is M the mass of the earth or of the satellite? Thank you, very helpful

Isn't kinetic energy equal to (GMm)/2r ?

This guy is adorable!