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All getting complicated now – https://solarsystem.nasa.gov/basics/grav/primer.php
Firstly well done for not using the word “inertia” once on this page you must be learning.
Quote:“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.
Quote:“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.
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.
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.
Quote: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
Quote: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.
Quote: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.
Quote: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.
Reffub – 6 minutes ago »
Quote: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.
Quote: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.
Quote: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.
Gravity is pulling the satellite down towards the centre of the Earth. How does the satellite stay up there if that is the only force. Talk about a daft argument.
Reffub – 15 minutes ago »
Quote: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.
Quote: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.
Quote: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.
If the bottle and the plumb bob want to travel in a straight line then they must be experiencing a force at a different angle to the current direction of travel, in the case of the plumbob one vector is directly opposite to the gravitational force as it gets higher from the ground.
grahamlthompson – 24 minutes ago »
Reffub – 6 minutes ago »
Quote: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.
Quote: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.
Quote: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.
Gravity is pulling the satellite down towards the centre of the Earth. How does the satellite stay up there if that is the only force. Talk about a daft argument.
I’ve already told you what that force is Graham.
It is Centripetal force
“force which acts on a body moving in a circular path and is directed towards the centre around which the body is moving.”
As you like Newton
“In Newtonian mechanics, gravity provides the centripetal force responsible for astronomical orbits.”
“Newton’s idea of a centripetal force corresponds to what is nowadays referred to as a central force. When a satellite is in orbit around a planet gravity is considered to be a centripetal force even though in the case of eccentric orbits, the gravitational force is directed towards the focus, and not towards the instantaneous center of curvature.”
Quote:If the bottle and the plumb bob want to travel in a straight line then they must be experiencing a force at a different angle to the current direction of travel, in the case of the plumbob one vector is directly opposite to the gravitational force as it gets higher from the ground.No your bottle isn’t experiencing a force at a different angle to the current direction of travel. When the car turns the car experiences a different force to the current direction of travel, the bottle is unaffected by the corner and just wants to carry on in a straight line, there is no force moving it.
As for your plumb bob it is on a string so it is experiencing some centripetal force during the change of direction.
Regarding the last part, Gravitational force is the weakest force, it can be easily defeated, need I say more.
Okay I feel I should of gone into a little more detail I kept it far too simple and I know Graham like things complicated, pity we can’t just discuss satellites and orbits etc but if cars help so be it.
G force in cars generally applies when they are forced into a change of direction/velocity, a driver secure in their seat during a corner will resist inertia and experience lateral G Force. But a bottle just sitting on the car floor will experience far less as it only has to overcome a tiny amount of friction and air resistance, to carry on its way. That is until it hits something solid.
The same could be said for an object sitting on the parcel shelf, in a head on accident it will have inertia, overcome resistance and fly forward, but it isn’t experiencing any real G force until it hits something solid.
As I said the plumb bob is secured to the car by a piece of string so that will experience a small amount of g force just a tiny amount of centripetal.
More to the point none of this applies to satellites in orbit, their velocity is constant, the gravitational pull of the earth is constant, as far as they are concerned they are traveling in a straight line.
Newton’s said gravity makes particles leave their straight paths. Next we will need to discuss Einstein’s general theory of relativity and that gravity is a distortion of space-time.
Another common misconception is that the ISS & satellites in orbit have Zero G, as already discussed there are no other forces pushing the satellite into outer space and so balancing Earths gravitational pull, there is only gravity and constant velocity.
That means the international Space Stations actual gravity at their orbiting altitude is still 89% of earths and yet the astronauts experience Zero G like conditions.
The reason is because they are a zooming (technical term) around the earth and constantly falling (just like satellites, okay technically the ISS is a satellite), the Vomit Comet (plane) uses a similar principle of falling to achieve Zero G like conditions for its passengers for about 30 seconds. The sub-orbital space tourism flights will only be going up and falling back down again for a few minutes.
To get true Zero G weightlessness you’d need to get a little further out into space.
Loved the rather silly ‘The Entire Universe’ musical extravaganza that was on at Christmas.
Gra, gra, gra, gra, gravity…..
Faust – 2 days ago »
All getting complicated now – https://solarsystem.nasa.gov/basics/grav/primer.php
Complicated but interesting, I’m presuming that getting a earth satellite into a higher orbit by using gravity assist involves firing forward thrusters slowing it down which will put it into a steep dive and then the earths gravity will hopefully increase its speed enough that it flys past the earth and ends up coming out at higher altitude. No doubt that still uses quite a bit of precious fuel but obviously a lot less than using thrusters alone (if that was even possible).
On that subject I think I read that it takes about 3 months normal fuel usage to move a geostationary sat to graveyard orbit, which isn’t that much higher. In fact we may need to use the current graveyard orbit in the distant future when the earths spin slows down slightly due to the interaction of the earth and the moons gravity. Which incidentally is why the moon (just another satellite falling around the earth) is slowly moving further away from us.
Obviously satellites don’t have enough mass to exert a noticeable gravitational pull on the earth, but once in orbit the earths gravity maintains their speed by constantly pulling them ‘down’ as they fall through space, speed and altitude are linked so they maintain their orbit. Regarding the pull ‘down’ bit by gravity you have to go back to projectiles, if you throw a stone it doesn’t just reach the apex of its flight and drop straight back down towards the centre of the earth, it’s the same with satellites but as they are in orbit they just carry on falling.
I see NASA call the Zero G falling floating effect on the ISS ‘Micro Gravity’.
I’m presuming everyone is up to speed now, on what force keeps satellites in orbit.
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