My Humax Forum » Freesat HD » HDR 1000, 1010, 1100S

Satellite installation

(28 posts)
  1. grahamlthompson

    grahamlthompson

    special member
    Joined: Feb '11
    Posts: 14,442

    offline

    aldaweb - 48 minutes ago  » 

    Reffub - 1 hour ago  » 
    There aren't any forces pushing a satellite into outer space, so there can be no balance between those forces and earths gravity. Once a satellite is in its desired orbit there is only one force acting on it and that is gravity.
    Satellite are just projectiles, slightly more complex than throwing a rock but the physics are the same.

    If there was only one force acting on a satellite and that was gravity it would very soon come back to earth.
    It needs a counter force to keep it from falling.

    Indeed. Stand a bottle of water on the floor of a car, get someone to hold the bottle while you accelerate to 30mph. Drive at a steady 30mph along a straight road and let go the bottle. It stands up as gravity is holding it down, now go round a corner at the same speed it falls over (the same force that tries to push an orbiting satellite out into space)

    | Sun 5 Feb 2017 14:52:02 #11 |
  2. User has not uploaded an avatar

    Reffub

    special member
    Joined: Jan '13
    Posts: 352

    offline

    grahamlthompson - 2 hours ago  » 

    aldaweb - 48 minutes ago  » 

    Reffub - 1 hour ago  » 
    There aren't any forces pushing a satellite into outer space, so there can be no balance between those forces and earths gravity. Once a satellite is in its desired orbit there is only one force acting on it and that is gravity.
    Satellite are just projectiles, slightly more complex than throwing a rock but the physics are the same.

    If there was only one force acting on a satellite and that was gravity it would very soon come back to earth.
    It needs a counter force to keep it from falling.

    Indeed. Stand a bottle of water on the floor of a car, get someone to hold the bottle while you accelerate to 30mph. Drive at a steady 30mph along a straight road and let go the bottle. It stands up as gravity is holding it down, now go round a corner at the same speed it falls over (the same force that tries to push an orbiting satellite out into space)

    For the sake of argument aldaweb is right stable satellites in orbit are constantly falling back towards earth they just don't hit Earth. (More on that later)
    Things come into motion because a force is acting upon them, a rocket carrying a satellite into space for example. Once that satellite is in orbit it is going fast enough to NOT fall back to earth, there is no need for any other force to act upon it apart from gravity. (Yes Graham pointed out photons can exert a tiny force, but do we really need to worry about that ?)
    If it was possible to throw a stone fast enough it would go into orbit, plenty of large stone like objects and water ice have orbited in space for billions of years, Saturn's rings for example. There is no counter force holding them all in orbit, seriously does anyone really think inertia can not counteract gravity for billions of years ?

    | Sun 5 Feb 2017 17:05:37 #12 |
  3. User has not uploaded an avatar

    Reffub

    special member
    Joined: Jan '13
    Posts: 352

    offline

    Because the object in orbit is no longer continuing in a straight line, it's inertia generates a force that tries to move the satellite out towards space. When the downward force from gravity balances the outward inertial force the object is then in a stable orbit.

    It seems like your describing a kind of centrifugal force, when actually it is centripetal force supplied by gravity that stops a satellite following its inertia and going off into space. Yes centripetal is another force but it is still just gravity. As I said before satellites are constantly falling back towards earth.
    If I might para phrase a website..... once a satellite is launched it will fall towards the Earth with a trajectory which matches the curvature of the Earth. It will fall around the Earth, always accelerating towards it under the influence of gravity, yet never colliding into it since the Earth is constantly curving at the same rate.

    | Sun 5 Feb 2017 17:16:44 #13 |
  4. grahamlthompson

    grahamlthompson

    special member
    Joined: Feb '11
    Posts: 14,442

    offline

    Reffub - 1 hour ago  » 

    Because the object in orbit is no longer continuing in a straight line, it's inertia generates a force that tries to move the satellite out towards space. When the downward force from gravity balances the outward inertial force the object is then in a stable orbit.

    It seems like your describing a kind of centrifugal force, when actually it is centripetal force supplied by gravity that stops a satellite following its inertia and going off into space. Yes centripetal is another force but it is still just gravity. As I said before satellites are constantly falling back towards earth.
    If I might para phrase a website..... once a satellite is launched it will fall towards the Earth with a trajectory which matches the curvature of the Earth. It will fall around the Earth, always accelerating towards it under the influence of gravity, yet never colliding into it since the Earth is constantly curving at the same rate.

    As I said before you are simply trotting out the same information you have read without fundamentally understanding it. The fundamental principle on which the maths is based on is, if an object in orbit is staying at the same altitude there must be two forces in equilibrium, as you say the object is falling at the same time as it is rising. You totally ignore why this is so, even that both are exactly the same principle. Gravity is one force, the other is derived from the velocity od the moving object. it mass and the deviation from a straight line. A moving object with any mass deviated from it's path by an external force generates an opposite force, the trick here is that the two have to be exactly equal and opposite.

    As you have already stated within the limits of the Earths gravitational pull that will normally adjust the altitude to compensate and hence the orbital period. Apply enough force to increase the velocity (required to change the velocity) to a level where the velocity becomes too large the object breaks free from the Earths Gravity and heads off into outer space, do it the opposite way the object descends to a level where it hits the atmosphere and falls out of orbit.

    Slingshotting a space vehicle to the outer limits of the Solar System utilises this in a big way. By subtly adjusting the object track you can gain a massive increase in velocity by utilising the gravity pull of the planets (Incidentally Gravity is the weakest known force in the Universe). The principles that Newton developed in the fundamental laws of motion are way stronger.

    Why do you think the bottle falls over, according to you the only force is gravity which is pulling straight down on the bottle ? Turning the car wheels to turn left or right generates a force because the bottle no longer travels in a straight line (just like the satellite) that cause the bottle to fall over. Where did this come from ?

    If it wasn't for friction and air resistance an object on the ground on a flat surface would behave the same way. Introducing a gradient has the same effect of deviation from a straight line.

    Imagine an object in deep space travelling at a specific velocity in a straight line and you produce thrust from a rocket thruster directly opposite to the direction it's travelling in. There is only one force directly applied, does it stop dead or even reverse, of course it does not. According to your weird ideas it should. Why not ?

    | Sun 5 Feb 2017 19:12:21 #14 |
  5. grahamlthompson

    grahamlthompson

    special member
    Joined: Feb '11
    Posts: 14,442

    offline

    Suggest Reffub reads this

    http://www.physicsclassroom.com/class/newtlaws/Lesson-4/Newton-s-Third-Law

    | Sun 5 Feb 2017 22:11:37 #15 |
  6. User has not uploaded an avatar

    Faust

    special member
    Joined: Jun '13
    Posts: 1,598

    offline

    All getting complicated now - https://solarsystem.nasa.gov/basics/grav/primer.php

    | Mon 6 Feb 2017 8:46:29 #16 |
  7. User has not uploaded an avatar

    Reffub

    special member
    Joined: Jan '13
    Posts: 352

    offline

    Firstly well done for not using the word "inertia" once on this page you must be learning.

    "Because the object in orbit is no longer continuing in a straight line, it's inertia generates a force that tries to move the satellite out towards space. When the downward force from gravity balances the outward inertial force the object is then in a stable orbit."

    Just noticed you said "No longer continuing in a straight line" ? Can I ask when was it ever traveling in a straight line ? Even the rocket that launched it didn't travel in a straight line.
    The second part is on the web and it is simply wrong, don't believe everything you read.

    "Gravity is one force, the other is derived from the velocity od the moving object."

    So now you've stopped using 'inertia' and you seem to think velocity is a force ? Ummm

    Yes we know they have thrusters for minor adjustments and an end of life higher orbit etc, but once released from the rocket we can happily say it is unpowered and that means it is a projectile.

    Now look up the 'Trajectory of a projectile' and tell me where 'inertia' comes into the equation. Unpowered objects don't travel in a straight line they are acted upon by gravity, friction and aerodynamic drag. Oh and don't forget photons
    If a challenger 2 main battle tank could firer a shell fast enough it could theoretically get that shell into orbit, it will carry on falling but due to the curvature of the earth will never hit it. It isn't that complicated it ain't rocket science.

    | Mon 6 Feb 2017 12:05:06 #17 |
  8. User has not uploaded an avatar

    Reffub

    special member
    Joined: Jan '13
    Posts: 352

    offline

    grahamlthompson - 14 hours ago  » 
    Suggest Reffub reads this
    http://www.physicsclassroom.com/class/newtlaws/Lesson-4/Newton-s-Third-Law

    "For every action, there is an equal (in size) and opposite (in direction) reaction force. Action-reaction force pairs make it possible for fish to swim."

    Why thank you Graham great link above, but absolutely nothing to do with a satellite minding its own business while orbiting the Earth. Yes if it fired its thrusters then Newton's third law would be relevant, and it could swim its way through space. But we aren't discussing powered flight are we.

    | Mon 6 Feb 2017 12:36:03 #18 |
  9. grahamlthompson

    grahamlthompson

    special member
    Joined: Feb '11
    Posts: 14,442

    offline

    Velocity creates a force, why does a satellite change it's altitude when you speed it up, without there being a force created in a upwards direction ? It stops gaining altitude when gravity regains equlibrium. Why does the bottle fall over when you go round a corner ? Why would a plumb bob suspended in a moving vehicle deviate from vertical when the car goes round a corner at a constant speed ? A train crossing the Nullarbor desert travels in a straight line for around 300Mls. The world land speed vehicle travels in a straight line, there's no way it could go round a corner at around 1000mph. A object in space will travel in a straight line until it gets affected by gravity or some sort of reaction thruster is fired.


    Newton's First Law of Motion states that a body at rest will remain at rest unless an outside force acts on it, and a body in motion at a constant velocity will remain in motion in a straight line unless acted upon by an outside force.

    https://www.grc.nasa.gov/www/k-12/WindTunnel/Activities/first2nd_lawsf_motion.html

    | Mon 6 Feb 2017 12:42:20 #19 |
  10. User has not uploaded an avatar

    Reffub

    special member
    Joined: Jan '13
    Posts: 352

    offline

    Velocity creates a force, why does a satellite change it's altitude when you speed it up, without there being a force created in a upwards direction ? It stops gaining altitude when gravity regains equlibrium.

    You're firing thrusters to speed it up change velocity, that is a force, of course it is going to change altitude, fire the forward thrusters and it will descend into a faster orbit. But with normal use and no thrusters gravity is the only force.

    Why does the bottle fall over when you go round a corner ? Why would a plumb bob suspended in a moving vehicle deviate from vertical when the car goes round a corner at a constant speed ?

    Because the bottle & plumb bob want to carry on travelling in a straight line. But then cars general don't orbit the Earth, if they did there would be an equal gravitational force on the car and its contents including the bottle and your plumb bob.

    A train crossing the Nullarbor desert travels in a straight line for around 300Mls. The world land speed vehicle travels in a straight line, there's no way it could go round a corner at around 1000mph. A object in space will travel in a straight line until it gets affected by gravity or some sort of reaction thruster is fired.

    Well done we are finally getting there, I've always said gravity and gravity alone is the only force.

    Regarding Newton's first law of motion, "a body in motion at a constant velocity will remain in motion in a straight line unless acted upon by an outside force."

    What's the problem the satellite is being acted upon by an outside source, it is called gravity so it won't be traveling in a straight line.

    | Mon 6 Feb 2017 13:26:28 #20 |

RSS feed for this topic

Reply »

You must log in to post.