# Search results

1. ### Finding mass of paperclip using Millikans theory

Assuming all the paperclips weighed the same, wouldn't it be fair to say that the mass of an envelop filled will a random number of paper clips will have a mass equal to the sum of the mass of the envelop and an integer multiple of the mass of a single paperclip? In otherwords, if the mass of...
2. ### Frictionless physics problem

1) Here are the equations you need: Circumference = 2*pi*Radius Speed = Distance / Time Centripetal Force = Mass * (Speed^2) / Radius So, if you know the Centripetal Force, what do you think the tension on the rope would be? 2) You should be able to use the equation for centripetal force I...
3. ### Proof: 0.9999 does not equal 1

You are correct, I only proved that a proof commonly used is incorrect. The title was misleading.

5. ### Proof: 0.9999 does not equal 1

The function y=1-1/x is often used to show how the repeating decimal 0.9999... is equal to 1. When x=1, y=1; x=10, y=0.9; x=10000, y=.9999, and so on. The limit of 1-1/x as x approaches infinity equals 1. An assumption is often made, however, that if the limit of an expression as x approaches...
6. ### Digital and quantized signal, are one same thing?

Generally, yes, but it depends. Digital audio is a quantized signal, but class D amplifiers (which quantize in the time dimension) are not considered digital. I guess you could think of digital as complete quantization.

30. ### Some true and false questions

It looks like you have the right idea.
31. ### Does light exerts force?

I think what you are talking about is called a radiometer. What causes it to spin is not the change in momentum from light "particles" hitting the paddles. In fact, the black side of the paddles absorbs much of the incoming light, causing the black side to heat up, while the white side stays...
32. ### Does light exerts force?

I don't think that light produces any force directly from its motion. The energy from light can cause a force to be generated, however. What exactly is your project?
33. ### Can absolute zero ever be achieved?

Great post Count Iblis! I agree with what you are saying.
34. ### Pure electrostatic

To create a transformer to change the voltage, you want to have the proportion of the number of output windings to the number input windings equal to the proportion of the output voltage to the input voltage. You can't reduce the current to truly be zero and still have anything flow, which...
35. ### Toboggan Speed Theory

Yes, and F=ma. Heavier people (assuming all else equal and that the fluid dynamics involved don't cause anything funky to happen) will accelerate faster than lighter people because the fixed force of air resistance will have less of an effect in terms of acceleration on the larger mass, but the...
36. ### Toboggan Speed Theory

Also, the force due to air friction slowing down the tobogganers is dependent on speed and surface area, not mass, but the force due to the combination of the normal force of the slope and gravity will be greater for heavier people, meaning heavier people of the same size and shape would be...
37. ### Doppler Effect.

If you want a way to think about why this must happen, you can think about it this way: In a given time period, the train has traveled a certain distance determined by its speed. Let's assume this train produced only two clicks, one at the starting point and one at the ending point. If you had...
38. ### Electical shock, electrocution questions

1) I'm not sure if this is the best answer, but air is a much better insulator than your body and your hand, so even a convoluted route through you and back out the other half of your finger will have less resistance than a path through only the air. 2) If there is a drain in this pool, and the...
39. ### Can absolute zero ever be achieved?

Well, it would be a violation of the Heisenberg uncertainty principle if you could detect the existence of such a particle. I don't see how its sole existence would violate it. Also, thermodynamics seems to be a field of probability. While energy tends to flow from high to low on average...
40. ### Calculating Normal Force

The formula typically used for this scenario is (The Force of Kinetic Friction) = (The Coefficient of Friction) * (The Normal Force) For the weight of the block, you should realize that both weight and force are the same units. For an object resting on a horizontal surface the normal force and...
41. ### Sound Intenisty at a Football Game

I think it's safe to assume that everyone is located an equal distance from the center of the field (otherwise we'd need more information). The first trick is to look at the decibel scale. dB is a logarithmic scale in reference to the power of the sound. If the power of two sounds are power1...
42. ### Budding SciFi Author with many questions

In terms of paraterraforming, I would think this would have to be set in the far distant future. Unless the population gets so high that there literally isn't enough room for everyone, it seems a little impractical. On Earth we already have tons of land, a decent atmosphere, and close to the...
43. ### Drag can happen in extremely low-viscosity fluids

Okay, here is my statement: "Even if the molecules in a fluid did not collide with each other, there would still be drag." It seems I misread some of the things russ_watters had posted, and thought he was arguing that Thomas2 was wrong that there would be drag if the molecules in a fluid did...
44. ### Faster than light.

If you rework what I did here with another distance in place of 1/2 of a light year: https://www.physicsforums.com/showpost.php?p=1584381&postcount=18 You will find that the speed you get is the same. So, distance doesn't matter with my calculations either. That doesn't prove that the distance...
45. ### Faster than light.

Tell me, how do you measure velocity? EDIT: This is the main purpose of Lorentz transformations: http://en.wikipedia.org/wiki/Lorentz_transformation#Spacetime_interval The idea is that the Lorentz transformations allow you to convert measurements from one observer to another when time is not...
46. ### Faster than light.

Why? Because then the distance between two events in space-time would not be the same for all observers. The theory of special relativity postulates that c is constant (it did not prove it) to make the math work out nicely.
47. ### Faster than light.

Of course you don't with the Lorrentz transformations. This is because each planet sees the other planet as being closer than it really is. Notice how in this example below, the perceived speed is lower than the actual speed:
48. ### Drag can happen in extremely low-viscosity fluids

The balloon talk was necessary for people to understand the number of collisions of air molecules with you every second. Otherwise, my explanation of drag would have made little sense.
49. ### Faster than light.

Let me rephrase what I said: Scenario 1: Planet A is at location 0 Planet B is at location -1ly Planet A sends a beam of light at c towards Planet B Planet B moves towards Planet A at close to c ================ Planet B will receive the light in a little over 1/2 year Scenario 2: Planet A is...
50. ### Faster than light.

Now, we could just as easily have a planet going very close to c towards us (only slightly less) instead of the light. Okay, so now if two planets 1 light year apart were traveling as close to c as possible towards each other, they could meet in only a little more than half of a year. Let's say...