News1 min ago
Gravity
Nothing to do with Arubahz's post below but can someone please tell me how gravity works.
I'm sure that ive asked something similar in the past but I just cant wrap my head around this.
If an object is spinning, then it will throw things AWAY from it, Not TOWARDS it.
A kids roundabout will throw scruffy little urchins towards the outer edges, not towards its centre. The Earth is spinning and yet it somehow attracts us all towards its centre (gravity)??
My knowledge of physics is abysmal.
Ta!
I'm sure that ive asked something similar in the past but I just cant wrap my head around this.
If an object is spinning, then it will throw things AWAY from it, Not TOWARDS it.
A kids roundabout will throw scruffy little urchins towards the outer edges, not towards its centre. The Earth is spinning and yet it somehow attracts us all towards its centre (gravity)??
My knowledge of physics is abysmal.
Ta!
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Its all to do with mass - everything that has mass has gravity. The Earth has a lot of mass therefore a lot of gravity, which can be seen and demonstrated. If you fall ten metres from a tree, even in Australia, gravity will rapidly attract you to earth and you will break.
Having said that, gravity is a weak force - where trees are concerned, 1g is enough to break your bones, but a sprinter leaving the blocks can easily exceed this.
Having said that, gravity is a weak force - where trees are concerned, 1g is enough to break your bones, but a sprinter leaving the blocks can easily exceed this.
Thanks Rob,
Now this is what I cant wrap my head around.
''Its all to do with mass - everything that has mass has gravity''
I was taught this in school, but cant find an example in real life!
I have a pretty big mass, (I'm overweight) what do I attract?
Mount everest is pretty massive, what does it attract?
The Earth is fairly large and yet the moon is actually receeding from it?
The big bang is quiet an event..and quiet a mass of , well mass, so why is is all flying away from itself. Shouldnt it all be coalescing? Not expanding?
Now this is what I cant wrap my head around.
''Its all to do with mass - everything that has mass has gravity''
I was taught this in school, but cant find an example in real life!
I have a pretty big mass, (I'm overweight) what do I attract?
Mount everest is pretty massive, what does it attract?
The Earth is fairly large and yet the moon is actually receeding from it?
The big bang is quiet an event..and quiet a mass of , well mass, so why is is all flying away from itself. Shouldnt it all be coalescing? Not expanding?
"I have a pretty big mass, (I'm overweight) what do I attract?"
Everything! But big your mass may be to you, it's tiny relatively speaking. Gravity is a weak force, remember - things have got to be pretty big for their gravity to be noticeable.
"Mount Everest is pretty massive, what does it attract?"
Everything, as above.
"The Earth is fairly large and yet the moon is actually receding from it?"
Both correct. The moon's velocity is just sufficient to cause it to be receding from the Earth at about a couple of inches a year but, eventually, it will stabalise.
"The big bang is quiet an event"
I think you mean 'quite an event'. At the time of the big bang, there was no gravity at all. In fact, there was nothing of anything at all!
"Shouldn't it all be coalescing? Not expanding?"
There was a theory for a while that there might not be enough matter in the universe for it to expand to infinity and that, at some time, it may began to fall back in on itself in a "big crunch". There was even a theory that this might already have happened more than once! However, this theory is now not widely believed and it is now thought that the universe will continue to expand until there is nothing left and the last star will simply burn itself out.
Everything! But big your mass may be to you, it's tiny relatively speaking. Gravity is a weak force, remember - things have got to be pretty big for their gravity to be noticeable.
"Mount Everest is pretty massive, what does it attract?"
Everything, as above.
"The Earth is fairly large and yet the moon is actually receding from it?"
Both correct. The moon's velocity is just sufficient to cause it to be receding from the Earth at about a couple of inches a year but, eventually, it will stabalise.
"The big bang is quiet an event"
I think you mean 'quite an event'. At the time of the big bang, there was no gravity at all. In fact, there was nothing of anything at all!
"Shouldn't it all be coalescing? Not expanding?"
There was a theory for a while that there might not be enough matter in the universe for it to expand to infinity and that, at some time, it may began to fall back in on itself in a "big crunch". There was even a theory that this might already have happened more than once! However, this theory is now not widely believed and it is now thought that the universe will continue to expand until there is nothing left and the last star will simply burn itself out.
Depends on how you view it.
Mass distorts the space around it. You msy have seen pictures of a visual represntation which show a "sink hole" where mass is. So anything nearby falls into the hole and in effect moves towards the mass causing it.
The spinning thing is a different matter. Things continue to move in a straight line unless acted upon by a force which changes direction. So something loose on a spinning object doesn't curve with it but continues in a straight line, thus flying away at a tangent.
The two situations can act against each other, with one or other winning out.
Mass distorts the space around it. You msy have seen pictures of a visual represntation which show a "sink hole" where mass is. So anything nearby falls into the hole and in effect moves towards the mass causing it.
The spinning thing is a different matter. Things continue to move in a straight line unless acted upon by a force which changes direction. So something loose on a spinning object doesn't curve with it but continues in a straight line, thus flying away at a tangent.
The two situations can act against each other, with one or other winning out.
nailit - when you stand on the surface of the earth this are two forces acting on you. One is gravity, which attracts you to the earth, the other is centrifugal force (due to the earth spinning) which is trying to throw you off into space. If the earth were to spin faster the centrifugal force would increase and eventually, when the centrifugal force became greater than the gravitational pull, you would be thrown off into space. If you stand on the equator you are travelling at about 1000mph; it requires a speed about 25 times greater than that to throw you off into space so, if the earth rotated once an hour instead of once a day things could start to get tricky. It also follows that if you stand at the north or south pole your speed is zero, so you will weigh slightly more there than you do on the equator because there is no centrifugal force acting on you.
Launch pads for rockets are usually sited near to the equator to take advantage of this and they also travel eastwards to add their velocity to the rotational velocity of the earth.
Launch pads for rockets are usually sited near to the equator to take advantage of this and they also travel eastwards to add their velocity to the rotational velocity of the earth.
nailit - going back to your Big Bang question - think of an explosive going off just under the surface of he earth. The soil/rock etc above it is thrown into the air AND THEN IT COMES BACK DOWN AGAIN as gravity attracts it. The same is true of the big bang - all matter was thrown outwards by the explosion but gravity is attracting it and it will slowly turn round and converge again (if the theory is correct). It's just that it takes rather longer than it does for the debris from an explosion to return to earth due to the distances and masses involved.
Your physics teacher is wrong (sort of).
Centrifugal force is best described as a "fictitious" force. If you write the equations of motion in a rotating frame of reference then a term corresponding to centrifugal force appears.
So it's real but it isn't -- an artefact of how you describe the system, but still necessary to understand it.
Centrifugal force is best described as a "fictitious" force. If you write the equations of motion in a rotating frame of reference then a term corresponding to centrifugal force appears.
So it's real but it isn't -- an artefact of how you describe the system, but still necessary to understand it.
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