Longshadow Loc: Audubon, PA, United States

clemente21

That is why the Kennedy Space Center is in Florida. Also, why the Russians launch from Kazakhstan. The closer to the equator, the more the Earth's angle velocity helps launching rockets.

Don's Leica Loc: Asheville, NC

FredCM asks if anyone has found gravitons yet. I am amazed at the recent discovery of gravity waves by means of very expensive research instruments confirming Einstein's predictions. The Wikipedia article on gravitons discusses string theory, which is way beyond my understanding. Maybe someone else can answer Fred's question.

Howard5252 Loc: New York / Florida (now)

The rocket needs to overcome the gravitational force being acted upon it at every distance from the earth as it rises. As the distance above earth increases, the gravitational force decreases. The amount of fuel needed must be enough to get the rocket to the point where gravity no longer has a noticeable effect. So it becomes a balancing between how much fuel can be carried and how quickly that point where gravity won't pull the rocket back.
I've always thought that if you had a long enough ladder, you could simply climb away from earth.

alberio Loc: Casa Grande AZ

Try figuring it at gallons per hour instead of mpg.

bobmcculloch Loc: NYC, NY

I believe that is caused by the gear ratios and the torque peak of the engine, top gear at the peak torque is supposed to give the best mileage, I have MPG gauges on both Subaru's and best mileage is usually between 55 and 65 on level ground,with or without the AC on.

Bunko.T Loc: Western Australia.

50 MPG @ 40 mph is better than 40 MPG @ 65 MPH, BUT at slower speed it's expected. The trip takes longer at lower speed, so Gallons per trip may be more. Haven't calculated that??

jeweler53

You can't be serious. MPG is the factor that matters if you want a trip that uses "less gas" Speed is irrelevant.

Longshadow Loc: Audubon, PA, United States

If you cover the same distance, 50MPG uses less gas than 40MPG would use.
At 50MPG going 50 miles uses 1 gallon.
At 40MPG going 50 miles uses 1.25 gallons.
The time to do the 50 miles will change between the two speeds.

CaptainBobBrown

Newton thought about speed to orbital velocity incrementally. That is, he thought of a canon ball shot over the horizon in a parabolic trajectory at successively higher and higher speeds until it no longer would come back to earth. This thought experiment is what led him to the far broader conclusion that objects in space revolving around another object must simply be moving at sufficient speeds to avoid "returning to earth". It's one of the reasons that the story about being hit by a falling apple is considered unlikely.

If you watch Space X launches you know that their launches in the past year or so always involve shutting down or throttling back their Merlin engines to reduce stress at the point they reach Max Q (maximum aerodynamic stress due to the combination of velocity and atmospheric density). Resistance to motion through the atmosphere increases exponentially with speed but to reach orbit you have to have enough speed to get past the point where air resistance plus gravity pull you back. In principle, if you had enough time and energy you could get to outer space but without the velocity necessary to stay in orbit above the horizon you'd always get pulled back to earth because persistent orbiting requires velocity as described by Newton's laws of motion and Kepler's formulations of elliptic orbits.

jayluber Loc: Phoenix, AZ

If you fire a rifle bullet straight up at 3,500 ft per sec, it will soon fall back to the surface of earth. If you fired a bullet upwards at 25000 mph (plus effect of friction with the atmosphere) it would continue forever and escape earth's gravity as it extends infinitely into space.

An object could escape earth's gravity at 1 mph with continuous thrust.

Hope this helps.

John_F Loc: Minneapolis, MN

From Wikipedia.

For a spherically symmetric, massive body such as a star, or planet, the escape velocity for that body, at a given distance, is calculated by the formula[3]

v_e = \sqrt{\frac{2GM}{r}},

where G is the universal gravitational constant (G ≈ 6.67×10−11 m3·kg−1·s−2), M the mass of the body to be escaped from, and r the distance from the center of mass of the body to the object.[nb 2] The relationship is independent of the mass of the object escaping the massive body. Conversely, a body that falls under the force of gravitational attraction of mass M, from infinity, starting with zero velocity, will strike the massive object with a velocity equal to its escape velocity given by the same formula.

Ballard Loc: Grass Valley, California

Escape velocity can be thought of as the amount of energy required to escape a given gravitational field and never get pulled back in. The energy required is linearly proportional to the mass that you impart that velocity to, so if you double the mass you double the energy required but the escape velocity remains the same. The escape velocity is assuming that you instantly have this velocity and don’t add additional energy after that point. So if you slowly add kinetic energy you don’t need the escape velocity to escape the earth, you just need to add the necessary energy whether it is added all at once or over time.

For those interested
The way to calculate escape velocity is to figure out the energy required and set it equal to kinetic energy and solve for velocity.
Since force over distance is energy you integrate Gravitational force over distance. So for escape velocity from earth G(gravitation constant)* M1 (mass of earth) * M2 (mass of object that you want to impart the energy too) / R**2 (R is Radius of Earth squared). If you integrate that from R (radius of Earth) to infinity you have force through a distance that gives you energy to escape the gravitational field. GM1M2/R**2 integrated from R to infinity gives GM1M2/R. Set that equal to kinetic entry, ½M2v**2 solve for v and you get square root of (2GM1/R) = v. Note: M2 cancelled out so escape velocity is that same for any mass and only M1 the mass of the object you are escaping from and its Radius matters. (This assumes that you are starting from the surface, if you start higher up then R is larger and the escape velocity become less).

RichinSeattle

[quote=jerryc41] ... In order to break away from the earth's gravity and go into orbit, a rocket has to achieve an escape velocity of about 25,000 MPH. …

A couple misconceptions in your question:

1) A body needs to be moving at 18,000 MPH (not 25,000) to remain in "low" orbit around the Earth without further power. It's still under the effect of Earth's gravity, but, at 18K MPH, parallel to the Earth's surface, it "falls" around the Earth, rather than back towards the source of gravity (the center of the Earth).

2) Escape velocity is the speed needed to leave the effect of Earth's gravity without further power, and that is ~25,000 MPH. The key phrase there is, "without further power." You (and Andy Griffith) are absolutely correct IF you have a source of continuous thrust - sufficient to keep the spaceship (or whatever) accelerating away from the source of gravity. The engine that can do that does not (yet) exist, but will someday and will undoubtedly be nuclear (fission or fusion) powered. Stick around; space travel should get interesting again.

BTW, I was a physics major at the UW until I realized how much work it takes to stay in orbit (class).

Longshadow Loc: Audubon, PA, United States

[quote=RichinSeattle]

I thought 25,000 MPH was the initial velocity for a ball to leave earth's gravitational field NOT go into orbit.
See above,
read all instructions before launching.......