3,868 reputation
1813
bio website none
location San Mateo, CA
age 59
visits member for 3 years, 5 months
seen 29 mins ago

8h
comment How to convert measurements in a game world to real life measurements
For a vertical launch, the time of flight is $t=\frac {2v}g$ You can measure the time, so get $v$. Then the maximum height is attained halfway through at $h=v\frac t2-\frac 12g(\frac t2)^2$ Count the pixels it goes up and you can divide to get the size of a pixel.
8h
comment How to convert measurements in a game world to real life measurements
I disagree with closing the question. With the usual no friction approximation and assuming they use the proper $g$, from the time of flight on a vertical launch you can derive the launch velocity. Then from the height attained in pixels you can derive the size of a pixel. Changing the launch to $45^\circ$ and seeing if the path is a parabola with the proper height and range is a reasonable check that the dynamics are right. True, they might not be.
1d
comment Is a given charge density a surface charge density or volume charge density?
If you don't, consider a cylinder that crosses the surface, large in diameter compared to the height. There is no E field through the sides of the cylinder, only through the circular faces. Use Gauss' law to find the difference in E field between the two circles.
1d
comment Is a given charge density a surface charge density or volume charge density?
You have the E field between the conductors given in the problem by taking the derivative of the potential. You know the E field is zero inside the conductors. This gives you a step change as you cross the surface of the conductor, caused by the surface charge. That is where I say you should have an equation for the step change in E field caused by a surface charge.
2d
comment Is a given charge density a surface charge density or volume charge density?
There is no volume charge density in conductors, because it would set up an electric field in the conductor, which it cannot support. If you have an insulator, you might have (and would expect it to be) a volume distribution.
2d
answered Is a given charge density a surface charge density or volume charge density?
Sep
28
answered Does the photoelectric effect require a battery or a circuit?
Sep
27
answered Steam above meal
Sep
26
revised Why doesn't this perpetual motion machine work?
added 1 character in body
Sep
26
comment Why doesn't this perpetual motion machine work?
This does not answer the question of why the given machine will not work. The power for the spring can be negligible. You are right that if we have an electromagnet things are different, but that was not the question. In questions like this we don't worry about things failing.
Sep
26
answered Why doesn't this perpetual motion machine work?
Sep
24
answered Binary Mass Function Plot
Sep
23
comment Cable being pulled at more than two points with a load at one end
As I understand it, A is the end of the rope at the upper right, B is the place where the rope attaches to the mobile pulley and C is the connection to the load. What does the rope at B connect to? Are there two ropes coming up from the load to the top left pulley, so if the load doesn't move neither does B?
Sep
23
comment Special relativity; rocket moving towards a mirror
@dmckee: I don't think this is a duplicate of that one. That one just was looking for a faster/slower than light answer. This one wants an actual calculation.
Sep
23
comment How can I find an error formula for density?
A partial derivative of a multivariable function with respect to one of the variables it depends on is just the ordinary derivative if you assume all the other variables are constants. So for your $p=\frac {4m}{\pi td^2}$ you have $\frac {\partial p}{\partial d}=\frac {-8m}{\pi td^3}$ by the power rule. I suggest you read the Wikipedia page I linked to.
Sep
22
answered Forces on objects orbiting a black hole?
Sep
22
answered Why don't clocks on a train read the same time?
Sep
19
answered Thermodynamics only deals with homogenous systems?
Sep
19
answered Propellers and the Speed of sound
Sep
19
comment Observing lunar lander and footprints on the moon?
The link you give has been updated with LRO photographs. They do show the hardware and even footprints.