Suddenly, I snap my fingers and turn the Sun into a black hole. What would happen to the Earth? The Kinetic Theory of Gases: What is the speed of a molecule in a gas? Now we know the velocity required to escape from a planet. This is equivalent to knowing the maximum velocity an object can have and still be gravitationally bound to that object. We next need to know how fast gas molecules move. Gases are characterized by their temperature, with the temperature determing the average velocity of a gas molecule.
According to the kinetic theory of gases developed in the 19th century, the amount of thermal energy per atom or molecule in a gas is given by the formula. Note that in a gas some molecules are moving faster and some slower than average. The distribution of velocities is known as the Boltzman distribution. Fully 0. But, as we shall see, it is these 0. As an illustration of a Boltzman-like distribution, think of cars on the interstate. Most are moving at speeds close to the speed limit of 65 mph.
However, a few are moving faster and a few are moving slower. And perhaps 1 out of ever cars is moving mph while another 1 out of is puttering along at 45 mph. Now supposed that a highway patrol officer pulls over and tickets the mph driver. What happens? Someone else speeds up and replaces the fastest car so that there is always one bozo driving much too fast.
At the distance of the snow line let's call this 5 AU , the temperature of material illuminated and heated by the Sun is about K C.
What is gravity? How do we put a spacecraft into orbit? Once a ship is in orbit, do we have to do anything to keep it there?
How did DS1 get into space? Could NASA use ion propulsion to put a ship into space? What is mass? This point was ably covered in the old Peter Sellers movie "mouse on the Moon" which had a steam kettle spaceship. Rockets usually just have to get high enough to fall into orbit.
However, you do need to get a rocket up to a high velocity before its fuel runs out if you want to send a probe to another planet. Phil Barker, Edinburgh Scotland The escape velocity refers to an the speed an object needs to achieve to move from its current point in a gravitational field to infinity as the gravitational field has no distinct end point , it is equal to the speed that the object would be traveling at if it was pulled by the same gravitational field from infinity to that same point.
However this only applies for an unpowered mass that would be constantly decelerating due to the gravitational pull of the plant and you are quite right in saying a powered mass would be able to escape no matter what its speed. Steven, Glasgow You'd have to go up a very long way indeed to escape the earths gravity. Remember that this is what holds the moon in its orbit. An orbiting object has not escaped gravity, it is in constant freefall towards the earth.
As long as it goes fast enough, it never reaches the ground because the earth curves away beneath it. Howard, Haywards Heath West Sussex In theory, you're right, and if only Everest was taller, you could climb it all the way up to orbit as slowly as you damn pleased.
Let's assume there's 2 ways into space, the slow way and the quick way. The slow way is to have some sort of propulsion engine, at least big enough to lift the vehicle's weight e.
The problem is that the jet engine can't get the oxygen it needs after about 5 miles up. But that turns out to be a lot of fuel a HUGE lot of fuel that you would be carrying, all the way up to 25, miles high or so where gravity becomes negligible and where, ideally, the last drop of fuel runs out.
That brings us to the quick way: use that fuel in one quick burst, accelerate to 11km per second 25, MPH as fast as possible, then coast the rest of the way with empty tanks and a dead engine. That way, you're carrying spare fuel for the shortest possible time. Paul Reilly, London UK You are right, but in order to "keep going up" on sustained power you'd have to carry immense reserves of fuel to push you up.
When Isaac Newton first described the concept of escape velocity he was thinking of a ball shot from a cannon. And modern rockets are much like that, their fuel tanks can only push them up for a few minutes and from then on they have rely on their own inertia. If they don't reach escape velocity by then, they fall back or remain in orbit. Alejandro Pareja, Madrid Spain True, in theory any speed would do.
But in practice the difficulty comes from the trade-off between the rate at which you escape the Earth's gravity and the rate at which you consume the fuel needed to do so - and hence the fuel needed at take-off. If you ascended at 5mph, but had the typical fuel capacity of the shuttle and would be largely used up in 10 to 15 minutes, you'd only get up a couple of miles. Martin, Manchester UK Escape Velocity is the minimal velocity required to escape earth's gravity without applying any further force.
In this case, when any speed is maintained continuously a force is constantly applied. So the key point is the Force applied. Shravan Singh, Kolkata India An unpowered projectile needs escape velocity to travel arbitrarily high but a continually powered vehicle does not, of course.
When the vehicle is in orbit above the atmosphere almost any force will do to push it further out - hence the ability of puny ion drives to push craft into higher orbits. It's getting into orbit that takes all the power.
A grand space elevator is proposed to take the craft out to where the orbital speed is the rotation speed of the Earth's surface, so doing away with the flashy rocketry. Don't hold your breath. However, you are quite right that, if you have means of propulsion, such as a rocket ship, you can travel as slowly away from the surface as you like. Michael Hall, Canberra Australia A stone thrown upwards would need to achieve this speed, however the space shuttle coule go up as slow as required Assuming enough fuel reserves.
The distinction is whether the flight is powered or not. Lee, Leeds UK There is a big difference between an object being aimed vertically upwards and shot out of a cannon and a powered rocket. The ball shot from the canon receives energy only as it passes through the barrel, from then on it is unpowered and slows down as it climbs through the earths gravitational field.
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