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Bjarne
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Let say gravity suddenly decreased 10%, - for instance due to tidal friction etc...
How fast would a planet decelerate? -
How can this be calculated?
How fast would a planet decelerate? -
How can this be calculated?
Janus said:What effect would tidal friction have on gravity?
If you are asking what would happen to a planet's orbit if the gravity between it and the Sun suddenly(instantly) decreased by 10%, then it would enter a new orbit with its present distance at perihelion. For instance, the Earth would enter a orbit with a perihelion at 149.6 million km and an aphelion at 1.91 million km, with a period of 446.5 days.
In its climb to aphelion, it will slow to 23.5 km/sec from its present 30 km/sec, so in 223.25 days it will slow 6.5 km/sec. Off course it will regain that velocity as it falls back to perihelion.
If you are asking what would happen to a planet's orbit if the gravity between it and the Sun suddenly (instantly) decreased by 10%, then it would enter a new orbit with its present distance at perihelion. For instance, the Earth would enter a orbit with a perihelion at 149.6 million km and an aphelion at 1.91 million km, with a period of 446.5 days.
No, the orbit would increase to a longer period. Consider this:Bjarne said:I guess it must be a mistake, because when gravity (suddenly) decrease, the Earth would fall closer to the Sun. (and hence a shorter period). Anyway I understand what you mean.
By the way:
When radius (in a gravitation field) increase 100 times,
then (off course) acceleration du to gravity decreases 10.000 times (r^2) (100*100)
BUT the orbit velocity only decreases 10 times, - why not more than that?
I wonder: why gravity is 1000 times weaker than the orbit velocity.
How is the orbit velocity and force of gravity "connected?"
Janus said:The energy can also be expressed as:
[tex]E = - \frac{GMm}{a}[/tex]
where "a" is the semi-major axis of the orbit, or average orbital distance.
acr said:Isn't it
[tex]E = - \frac{GMm}{2a}[/tex]
?
The virial theorem states that
[tex]
<E> = 1/2<U>
[/tex]
and it can be shown that
[tex]
<U> = - \frac{GMm}{a}
[/tex]
Orbit velocity is the speed at which an object must travel in order to maintain a stable orbit around another object, such as a planet or a star.
Orbit velocity can be calculated using the formula V = √(GM/R), where V is the orbit velocity, G is the gravitational constant, M is the mass of the central object, and R is the distance between the two objects.
The factors that affect orbit velocity include the mass of the central object, the distance between the two objects, and the gravitational constant. Other factors such as atmospheric drag and external forces may also have an impact on orbit velocity.
Orbit velocity is important because it determines the stability of an orbit. If an object does not have the correct orbit velocity, it may either crash into the central object or escape its orbit completely. Orbit velocity is also crucial for space missions, as it helps determine the trajectory and duration of the journey.
Orbit velocity can be changed by altering the speed or direction of the object. This can be achieved through the use of thrusters, gravitational slingshots, or atmospheric drag. However, changing orbit velocity requires careful planning and precise calculations to avoid any potential dangers or disruptions to the orbit.