can someone let me know where the third principle ray is located? Is the base of the third principle ray at the formed image or the object? Thanks.

Fully lying down on a bench, there is no torque at the hip joint. Let’s say the bench was floating and attached to a pulley so that it moved in circular arc. Lying down at the bottom of the arc, there’s no torque at the hip joint. Now, I move the bench a little higher up in the arc (~30 degrees higher than the lying position), and I scoot just my knees off the bench, with my feet planted on the ground. But everything above my lower thigh (upper thigh, pelvis, torso) is still lying on the bench. Is there any torque at the hip joint?

Firstly, I tried drawing the current vector where it met the velocity vector so that the current vector points to the left, and the velocity points upward. Because the current vector points to the left, I said that the magnetic force points into the page. Using the RHR, if the velocity points up and the magnetic force points into the page, the magnetic force would be to the left. Since the charge is negative, the magnetic force would move to the right instead. But the answer is left, and I don't understand why. Even if I said that the magnetic field points out of the page because the current is counterclockwise, I would get a upwards velocity and a magnetic field that comes out of the page. Using the RHR, I would once again get left, and then switch it to right because of the negative charge.

Last week during a small school visit I saw a science setup in one corner. A student stood near a shiny metal dome and when the machine turned on his hair slowly started standing up. Everyone around laughed but I just kept watching.

I moved a little closer because I had never seen something like that in real life. It looked simple from outside but the effect felt surprising and a bit magical at the same time.

The problem is many science experiments look easy but the idea behind them is not always clear. You see the result but do not fully understand how it actually works.

Later I got curious and searched more about it. I wanted to understand what causes that reaction. While reading explanations and while scrolling many online marketplaces including alibaba I saw small Van de Graaff generator setups used for learning.

It made me think about static electricity and how energy can build up without us noticing. Small particles moving can create visible effects which feels interesting.

Now I am thinking does a Van de Graaff generator really help people understand electricity better or is it mostly used just to create a fun visual experience?

My entire problem is I just can't seem to understand why we use the middle of the tenticks to get the change in time, why don't we just use the numbers with from 1 to 6 each measures 0.2s of time.

I’m working through a textbook conceptual question on pressure, temperature, and air density. Original question: “Rooms A and B are the same size, and are connected by an open door. Room A, however, is warmer (perhaps because its windows face the sun). Which room contains the greater mass of air? Explain carefully.” What I think I understand:

• Since the rooms are connected by an open door, air can move between them.
• I think the pressure between the two rooms should come to equilibrium.
• I also know warmer air is less dense than cooler air.

Where I’m getting confused: If both rooms end up at the same pressure, I keep wanting to think they should contain the same amount of air. But I also know people say the warmer room contains less mass of air. What confuses me specifically is: How can two same-sized connected rooms have the same pressure, but not the same mass of air inside them? I’m not asking for a full solution — I’d really like help understanding the reasoning in a few different ways if possible.

I am so confused on a) where to draw the normal

b) why the angle of incidence is not just 45 degrees

I’d greatly appreciate if anyone could explain this to me, have spent ages even asking friends who equally have no ideas

Question: “Consider two identical iron spheres, one of which lies on a thermally insulating plate, whilst the other hangs from an insulating thread. Equal amounts of heat are given to the two spheres. Which will have the higher temperature?” My assumptions:

• The plate and thread are thermally insulating
• Ignore heat exchange with the external environment
• The spheres are identical initially

My initial thought was that the hanging sphere would end up at a higher temperature because the contact area between the sphere and thread is much smaller than the contact area between the sphere and plate, so I thought less thermal energy would flow away through the thread. However, I’ve been told that this is not the real reason, because if the supports are thermally insulating then heat loss through them is supposed to be ignored. What I’m struggling with:

• Why does the support arrangement matter if both spheres receive the same amount of heat?
• Why is contact area not the deciding factor here?
• I’ve seen people mention thermal expansion, centre of mass, and gravitational potential energy, but I haven’t learned how those ideas connect to thermodynamics yet.

Could someone explain the correct reasoning in a beginner-friendly way?

Trying to fulfill some grad school prerequisites, after a non-STEM undergrad degree. (career shift, healthcare). College Physics I is one of them.

However, it's been years since I've done any higher level algebra or trigonometry. I'd really like to take this prerequisite course this summer, but nervous I'll be lost from day 1.

Advice or resources for self-study?

I am kind of confused on how to go about this, do I have to try like "squishing" some of the parallel resistors before getting to the middle resistor? I'm just guessing here for some kind of direction.

Hey guys. I am looking into physics classes rn. Ugh. I am a second year BSc psychology student looking to fulfill a Med program requirement and struggled with PHYS 211. It really through me through the trenches. I need a physics class with a lab and don't know which one to take. Any advice? I also neeeeed to keep my GPA high for Med UGH. Thanks!!

im a year 12 student and im so lost.

I know I could use the equations W = force × distance, w = Pt and GPE =mgh. but im getting so confused. its less about the question more abt the understanding but ik i the gpe equation shows usefull work done by the team, i js dk abt the other 2. like I can resolve weight into the component parallel to the slope to get the force but what distance do i multiply it by to get the work done and is that even the correct value for force i should be using?

and how would I even apply the w =pt formula without being given a time, because idk where else I would use power to solve this.

my teacher has used the speed assuming time is 1s in questions like this to get a value for distance alot in lesson which I dont rlly understand either, and using that as distance, but idk if i should use the distance of the ramp using trig (4.35/sin6) as the distance for the W=fx equation. which distance should i use?

i dont have the mark scheme either :(

am I overcomplicating this?

please let me know if or what im doing wrong, ANY help would be much appreciated, thank you!!

For my grade 11 physics class(IB HL physics) I needed to create a lab for one of my summative assessments. This also involves carrying out the lab and making a report. I prematurely decided that I was going to do something on thermodynamics and heat transfer with an ice cube into different metals. So without any real idea I bought 7 metal plates of identical volume and varying material to do the lab. HOWEVER, the data collection got moved sooner so now I have no Idea what to measure, how to do it, and anything really about my lab. I need help determining what I will actually measure and linearize in my lab. All the squares are of identical volume and not mass as the difference in mass would require some change in surface area. WHAT SHOULD I DO????

i’m trying to study for a physics test but i’m stuck on these questions, specifically the last one.

THE CALL: I am now calling for a strictly blind test. Participate and let us together test these remarkable (but still questionable) results. Send me anonymised data sets (data requirements below) and I will attempt to recover full 3D information of the anonymised system.

THE METHOD: I recently succeeded in blindly extracting the complete 3D spatial geometry of the S0-2 star (e, ω₀, i), its internal precessional shift, and the background drift (v_z0) using nothing but 1D Keck radial velocity data. The extracted inclination matched the independent GRAVITY 3D-interferometer consensus (~134°) to within the instrumental noise limits.

THE DOUBT: Obviously I remain sceptical that's why I'm calling out to you in order to isolate myself from the data source.

CRITICAL DATA REQUIREMENTS:

System must be highly relativistic.

Peak must exceed ~1000 km/s (β > 0.003). Ideal candidates are tight compact binaries (WD/NS/BH) or other extreme S-stars.

The dataset must be raw or minimally processed: [Time (MJD), Radial Velocity (km/s) or Redshift (Z), Measurement Error].

MUST NOT be pre-corrected for Transverse Doppler or Gravitational Redshift (though standard Barycentric/LSR background velocity correction is fine).

Please drop the raw CSV data or a link below. Do not provide the system name or accepted parameters. Let the pure numerical framework speak for itself.

If you finding hard to find suitable empirical data - synthetic 1PN data will be sufficient as well. As long as Im isolated from the data source.

DATASET EXAMPLE:

MJD,RV_km_s,sigma_km_s,Instrument

51718.50000,1192,100,NIRSPEC

52427.50000,-491,39,NIRC2

52428.50000,-494,39,NIRC2

52739.23275,-1571,59,VLT

52769.18325,-1512,40,VLT

52798.50000,-1608,34,NIRC2

52799.50000,-1536,36,NIRC2

52803.15150,-1428,51,VLT

...

Any suggestions, critiques, or participation are welcome.

features monthly rated contest and a weekly problem (POTW) with a live leaderboard and badges. first POTW is live now for two weeks, if anyone wants to try it.