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.
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.
Did you find any ? I'm struggling to find one myself. I did for the record find a channel called allery chemistry but I didn't really watch it's videos yet.
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.
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! 🙌🏽🤯🔥🎊
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!
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.
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.
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.
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.
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?
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.
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.
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
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.
kurdman12345678 The curvature of spacetime due to earth does not push objects towards the earth rather when a object moves near the earth it tries to move in a geodesic path (path between two points that has the shortest length) but due to the curvature of spacetime around earth those geodesic paths are curved which tend to converge towards the earth.
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.
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.
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.
Really? I struggle to see why. G is a constant. M and m are both scalars. F and r are the only vectors in the equation. And F is in the opposite direction to r. It may be they want you to say that Force is the differential of potential energy and PE is always negative (because it increases as you go further away from the earth and is 0 at infinity)
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.
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
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.
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...
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.)
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 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
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.
Mass/field Vector of the universe acting upon accelerated mass. M=amG/c2r. The velocity of inward spherical wave's of future probability cascading down from a distance radius forming a spherical rings series compressing+4-0-4+decompressing eXpanding sphere's dissipating gravity dividing time same ratio information is being multiplied generating electrical potential oscillating the volume within mass at the expense of entropy of gravitational potential. Energy of gravitation =Eg= v+/-m +Mu G/r.
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!
DrPhysicsA Thank you for the reply. An interesting video indeed. But in fact i was thinking of the two bodies problem in the planetary context. I have read something with a reduced mass to write the exact equation of the movement of a satellite which ends with this r = K²/(GMt( 1 + e cos θ )). I didn't understood how to arrive to this result. I was hoping you could shine some lights. (Sorry for poor english)
All I have done is to take the 2 pi r into the square root. In order to to do that I had to square it first so that when you take the square root you get back to where you started.
DrPhysicsA I instead substituted v = 2 pi r / T straight into the equation and then rearranged for T^2 after squaring both sides. Thanks for the great video by the way :)
think's doctor for this demonstration,but in this cas ,the herth has 1 motion .but realy the herth mouvs in the orbit of the sun then all this calcutions was rang
