# Search results

1. ### B How many horsepower?

The power mentioned above for opposing rolling resistance and the drag is the minimum power needed to accelerate the vehicle to 300 mph. That acceleration will start with a high value, and continuously decrease as the speed increases, till the target of 300 mph is reached asymptotically. If you...
2. ### B How many horsepower?

Not the case here, since aerodynamic drag and rolling resistance should be taken into account.
3. ### B How many horsepower?

In my estimation, I accounted for the power lost to the transmission; thus, the 1600 HP is 'power to the ground', yes... If you have to keep that speed of 300 mph, even for the fraction of a second, you'll need the 1600 HP, for that fraction of a second... Good luck...
4. ### B How many horsepower?

To the aerodynamic drag, you must add the rolling resistance. The rolling coefficient for tires on concrete is around 0.012 Now, for a car with a mass of 3400 lb (1544 kg) the power needed to keep the car moving horizontally at 300 MPH (134 m/s) fighting just the rolling resistance would be...
5. ### B How many horsepower?

Assuming a frontal area of 1.5 m2, a coefficient of drag of 0.3 (a frequent value in sport cars) and an air density of 1.23, the power needed to keep the car moving at a constant 300MPH = 134 m/s against the aerodynamic drag would be: Power = drag × airspeed ⇒ Power = (½ × 1.5 × 0.3 × 1342 ×...
6. ### Could a ballistic missile be used to deliver cargo?

I believe that a system of 'rocket mail' was used in Austria or in Switzerland, in the 1920s or so, to send letters to villages that were difficult to reach by land. And, in 1810, Heinrich von Kleist proposed (I suspect that tongue in cheek...) a 'Bombenpost' service, with hollow shells and...
7. ### Hydraulic motor-AC generator coupling

Die Energie der Welt ist konstant (Clausius)
8. ### I Thoughts on Newton's Bucket and the relativity of rotation

Just a comment: some years ago, I tried to read about the history of the 19th and 20th century research on the problem of inertia. There was a document, a book, by Immanuel and Benedikt Friedländer that seemed to be interesting, but in spite of my efforts, I wasn't able to find it in the...
9. ### B Jet propulsion in space?

Perhaps all the bird wanted was a jetstream hike...
10. ### B Meaning of panchromatic

Panchromatic is a b/w film that is red-sensitive. Older, orthochromatic films, are also b/w, but red-insensitive.
11. ### B How come weight difference doesn't cause problems in trade?

Balance scales are widely used. The well-known 'Toledo'... Like this one... But I believe that the OP is right... These somewhat old-fashioned mass-comparing instruments have today been displaced by electronic scales that measure force, and not mass...
12. ### Parachutes for small planes -- so many lives saved...

Well, you haven't provided a single case of a plane saved by the parachute after a low-level stall/spin. No wonder you didn't... Once you enter a spin below -say- 500 ft, you are doomed, parachute or no parachute. Not even the manufacturers of those systems dare to make that claim, because they...
13. ### Parachutes for small planes -- so many lives saved...

If you know of a single case of a plane saved by the parachute after a low-level stall/spin, you should mention it... Extraordinary claims require extraordinary evidence...
14. ### Parachutes for small planes -- so many lives saved...

That's not correct. On the contrary, almost all planes, specially light ones, can easily exit from a spin. It is a procedure covered in the pilot operating handbook. It usually consists in easing the stick forward and pushing right pedal for left spin or vice-versa.
15. ### Parachutes for small planes -- so many lives saved...

Fatal accidents related to stall/spin use to happen at low altitude. If you have enough altitude for the deployment of a parachute, that altitude is also sufficient for a standard recovery maneuver. No need for a parachute...
16. ### Parachutes for small planes -- so many lives saved...

Most accidents in small planes are of the stall/spin type, and -in those cases- a parachute is of little use. If the engine stops because of a mechanical failure (or lack of fuel, something not at all unusual...) you can always glide the plane and land it, if more or less roughly... A parachute...
17. ### B Nuclear explosion legs

They are the wakes of sounding rockets, launched vertically just before the detonation with the purpose of detecting the winds associated with the explosion.
18. ### I How to calculate pressure in a bottomless aquarium

It's physics for 15-year old students... It's hard to imagine engineers and physics professors baffled by so simple a question...
19. ### Flat ending light beam

If the light moves in a fluorescent, highly refractive medium, say n=2, the cylinder may probably be seen as motionless by an observer moving at c/2 outside that medium...
20. ### Polish notation

You can still find the HP35s, and another model, I don't remember the name now, for financial calculations. Besides, and for nostalgics, you have the 'SwissMicros': https://www.swissmicros.com/ To my knowledge, there are no other brands of RPN calculators. Well, perhaps in Russia... In Soviet...
21. ### B What does a magnetic field consist of?

At the present time, lacking a satisfactory theory, both the magnetic and the electrostatic fields are temporary solutions in order to explain the 'action at a distance'. That was, too, the case of the gravitational field, until Einstein formulated his General relativity.
22. ### B Need help explaining river-boat problems

If any of them is familiar with flying, you can mention the frequent case of landing with a crosswind, when the heading and the course are at an angle that can be quite large for slow flight and strong winds. Of course, the plane is flying 'within the moving medium' ('Mobilis in mobili,' as...
23. ### B Need help explaining river-boat problems

This may also be of some help:

Correct...
25. ### B Need help explaining river-boat problems

Instead of an animation, I'd suggest a 'mental experiment'. Tell those skeptical canoe paddlers to imagine that the river is a solid moving surface, like a conveyor belt, and that their canoes are small cars. After a little reflection, sure all of them shall agree that crossing that 'river' is a...
26. ### I Hot air balloon descent

I'm not so sure... Millikan's drops were stable in mass and volume, but a descending hot-air balloon will probably lose volume and gain mass. That must result in a continually decreasing buoyancy. Hence, the speed will increase...
27. ### Steam engines -- A new idea, maybe...

It's an old idea, and one that didn't work, for the reasons stated above by russ_waters... http://douglas-self.com/MUSEUM/POWER/ether/ether.htm
28. ### First Nuclear-Powered Airliner?

How much power does an aircraft need? A rough estimate can be made as follows: for unaccelerated level flight at best L/D ratio, for a mass M and airspeed V, we may imagine that plane with engines off and gliding, under 'gravitational power'. That power will be the weight of the plane times the...
29. ### Why are air plane propellers small?

Cavitation takes place only in liquids, where a gas bubble may form and then collapse destructively. That never happens in air...
30. ### Why are air plane propellers small?

In general, it is cheaper to deliver a thrust through a large mass of air launched backwards at a small speed than with a small mass launched at high speed. The momentum of that mass, and the corresponding reaction of the aircraft, may be the same, but remember that the energy has the v term...