# Search results

1. ### Man versus Iron Weight

Duh ! It seems so obvious now ! Thanks, E.
2. ### Man versus Iron Weight

http://www2.uah.es/jmc/ai14.pdf On page 2 of the above pdf there is an example in a box with title 'Acceleration' which states that there is a difference between a man pulling on a rope with 600N force and an iron weight of 60Kg (g = 10) tied to the rope. The difference being that once the...
3. ### Thickness of bulb filament affect brightness?

I am interested to know why that is ... E.
4. ### I was changing a light pendant today

and considered doing this with just the switch turned off. After turning off the switch I checked the voltage with a meter in A/C mode. It was 140V which I thought a tad high. When I turned the switch on the reading was 230V as expected (in the UK). So I turned off the lighting circuit at the...
5. ### Power from F time v

Suppose you have a frictionless and perfectly balanced conveyor belt going into space (and back). The belt is driven by a motor on earth. Suppose you want to send a person who weighs 100kg into space and you boost them onto the conveyor belt at 1m/s with the conveyor belt running at 1m/s (the...
6. ### Why kinetic energy is proportional to velocity squared

Hi Jeff, I didn't give your posts due attention the first time I read them. They are very insightful (no math :smile:). Thank you. E.
7. ### Why kinetic energy is proportional to velocity squared

So then the rate at which the rocket gains kinetic energy DECREASES ? But the rocket's acceleration INCREASES ? And the explanation for both of these is that the rocket's mass is DECREASING ? E.
8. ### Why kinetic energy is proportional to velocity squared

No. I quoted what you gave for the EXHAUST GAS ONLY. Please re-read my question. I know my questions APPEAR stupid to you because you know the subject inside out, but I genuinely am just trying to understand this one bit at a time. E.
9. ### Why kinetic energy is proportional to velocity squared

Okay. I've worked through your math and am happy enough with it. In order to get some insight I started plugging in numbers. It appears that the faster the rocket is going the more energy is transferred to the exhaust gas \frac 1 2 \Delta m v_r^2 + \Delta m v_r\cdot v_e + \frac 1 2...
10. ### Why kinetic energy is proportional to velocity squared

Thanks again. I'm happy with the principle now, although I'm going to have a go at working through DH's rocket math just out of interest. E.
11. ### Why kinetic energy is proportional to velocity squared

Originally I thought that constant rate of energy supply would provide constant force so I was confused as to why energy out (KE) was proportional to v^2. Then as result of answers given here I was persuaded that a constant force would not result which explained why KE was not proportional to v...
12. ### Why kinetic energy is proportional to velocity squared

You are a bit over my head here, but when you say 'Since the mass is constant, the change in vehicle velocity is also proportional to energy transferred to the vehicle', is there a constant force on the vehicle ? E.
13. ### Why kinetic energy is proportional to velocity squared

No problem. What you explained earlier made sense. But I am confused again as I didn't follow DH's argument. If now 'Constant rate of fuel production does produce a constant force' I am back to square one. Can you explain DH's argument for me ? E.
14. ### Why kinetic energy is proportional to velocity squared

Thanks very much, I'm starting to get my head round it now.
15. ### Why kinetic energy is proportional to velocity squared

Thank you for your answer. I accept what you say as a fact. So my confusion is to do with why a constant rate of fuel consumption does not produce a constant force. Can you explain this please ? E.
16. ### Why kinetic energy is proportional to velocity squared

I am not disputing any of this. My big hangup is to do with energy = force x distance, so starting any answer with this fact (which I know is true even though it confuses me) is not going to help me. Say my rocket has mass of 1kg and converts energy E per second to produce 1N of thrust. In...
17. ### Why kinetic energy is proportional to velocity squared

I'm glad at least one person doesn't think I'm mad / stupid, even if I didn't fully understand your explanation. :rolleyes:
18. ### Why kinetic energy is proportional to velocity squared

But the reason I say that it goes into the same change in velocity is because it is constant acceleration caused by a constant force caused by a constant supply of energy. I am burning fuel (releasing energy) at a constant rate in time to create a constant force and yet my rocket is not...
19. ### Why kinetic energy is proportional to velocity squared

That is why I gave an example where 'it appears to me' that conservation of energy is violated ...
20. ### Why kinetic energy is proportional to velocity squared

That sounds promising. Assuming you understand why I am confused that energy is not proportional to v, can frame of reference be used to explain why it is proportional to v squared ? E.
21. ### Why kinetic energy is proportional to velocity squared

Thanks for guaranteeing that JT, but I'd prefer if you would explain it. Otherwise I'll have to use the Chewbacca Defense. E.
22. ### Why kinetic energy is proportional to velocity squared

Let me try a different wording. Say you have a rocket ship at rest with a certain amount of chemically stored energy (fuel). To provide a constant force to constantly accelerate the rocket the chemically stored energy is used up at a constant rate. This energy gets mainly turned into kinetic...
23. ### Why kinetic energy is proportional to velocity squared

I don't doubt this is true, I just don't understand it. Why does it take more energy to accelerate from 5 to 10 m/s than from 0 to 5 m/s ? Are these not the same just in a different frame of reference ?
24. ### Why kinetic energy is proportional to velocity squared

Thanks for your responses, but I'm still a bit confused. I understand the math and how kinetic energy is calculated as work done (force x distance). It's just that it doesn't make sense to me when I consider a propulsion system. If you are putting energy in at a rate proportional to time (to...
25. ### Why kinetic energy is proportional to velocity squared

Could someone please explain why kinetic energy is proportional to velocity squared and not just velocity. A propulsion system that provides a constant force would typically use energy at a constant rate in order to accelerate at a constant rate and thus rate of change of velocity would be...
26. ### Transmission Error Detection

Hi, I have a small fixed size packet of information that I want to transmit and detect errors with a high degree of confidence (no correction is required). I'm guessing that a CRC is probably the way to go but don't know how to work out what form of CRC to use. I want to be able to specify a...
27. ### Electron flow in a circuit

Doc Al, I always thought that the field in a circuit propogated at c such that a bulb many kilometers away from a switch would turn on almost instantly. Can the gradient you talk about really propogate that fast ? E.
28. ### Electric Field, Mass, Length

I believe the following are all true for an observer in a different inertial frame : An object's length is contracted in the direction of its motion An object's mass increases under motion The strength of an electron's field is reduced in the direction of motion The strength of an...