An apple falls to the floor. Straight down, as far as we can tell.
But how do people stay down, up-side-down, like in Australia? And why do we not spin off the globe as it turns around, and around.
And nobody can proof it. Not the scientists not anybody. They have explanations, but no proof.

But it is there.

Whatever you name it. We are stuck to the floor. So what is it?

To begin to answer that question: I will try to show what it is on a globe earth model. In another article I will try to explain what it could be on a flat earth model.

What is magnetism? I do not understand that. I cannot see it. But it is there. It is an attraction between two magnetic objects due to the Lorenz force.
And it is quite strong. Metallic objects are 'glued' to a magnetic sphere, and can stay glued even when the sphere is spinning fast.

But it is not gravity.

An example of what it is not is the 'spinning tennisball with water coming off'. Yes there is gravity applied to both water and tennis ball, but that is very small. The biggest mistake though is the amount of rotation of the spinning ball. Earth (as a globe) is spinning at 1 rotation per 24 hours. Even a drenched tennis ball will stay wet at that amount. Off course the earth is bigger, so the speed is larger. But even then the outward force is v2 / r = (465.1)2 / 6378000 = 216318 / 6378000 = 0,03392 m/s2, which is tiny compared to the downward force

You can measure it though.

The Cavendish Experiments shows there is an attraction between two masses. if done properly a number of amateur experiments are shown in this video. However they are amateur experiments, you should eliminate other forces acting on the masses, like wind blowing and the torsion on the wire, etc. Still they are nice examples of how to visualise it.

Gravity on earth is 9,81N (well on average) which corresponds with the acceleration of 9,81 m/s2 on earth's surface at sea level in a vacuum.

But not everywhere weight is different on the poles, than it is at the equator. And if you take a look at the weird picture on top of this section: It fluctuates all over the place.
And you do not need a satellite to see this for yourself. This is something you and I can measure for ourselves.

So how does gravity work in a globe earth model.

Gravity works on any two object. Yes even the smallest one. And, as is usual for a lot of forces, it acts upon the centre of mass. This means that the combination of all individual attractions is centred towards the core of the earth.

The force is very weak. And can be described with the following formula:

$$F = \frac{G * m_1 * m_2 }{ r^2}$$

So the larger the mass of either object, the stronger the force. But the more distant de objects are apart, the smaller (squared) it becomes. However G (the gravitational constant is very small (6.674×10−11 N·kg–2·m2)

The mass of earth is estimated as a little under 5.97 × 1024 kilograms. (That is kg). That is a lot of mass.
The mass of the moon is estimated as a little under 7.3 × 1022 kilograms.
The distance between the two centres of mass of the earth and the moon = 3.84 x 108 meters.

$$F = \frac{6.674 * 10^{−11} * 5.97 * 10^{24} * 7.3 * 10^{22} }{ {3.84 * 10^8}^2}$$

So the gravitational force between earth and moon = 1.971231020N

The gravitational force between as person of 75kg and the earth ≈737N. This is almost the same as 75 * 9.81.. but there is a lot of rounding errors there. But the formula checks out.

What is important about these figures is that the attraction between moon and earth is way bigger than between me and earth. Or between me and you, where ever you are.

So the force of gravity is more or less the same on the whole of the earth. It might differ because you are farther away from the earth's core, but even on mount Everest there would be only a 0,3% difference. (note: This does not take into account the position of Everest on the globe)

So how to explain the difference in weight? Well weight is not the same as gravitational force. You weight is a combination of several forces combined. One is the gravitational force, one other is the centrifugal force. This force (even though it is small) is larger at the equator than on the poles. At the equator you move at a 1,600 km/hour. At the poles you just turn around, and around.
Actually the earth bulges a little at the equator and this adds to the distance. The distance to the center of the Earth from the equator is 6,378 km. And the distance to the center of the Earth from the poles is only 6,356 km. That’s a difference of 22 km. So again in regards to the gravitational force this is small potatoes.
Meanwhile they have discovered the density of the mass below you also affects the size of the gravitational force. So these figures are just averages over the globe.

However: It will explain one thing (explain, not proof!), and that is: You won't fall of the earth, because you are at the south pole. The total effect of gravity is pointed towards the core of the earth and not down south. Besides: North and South being up and under is just the ancient European way of picturing the globe.

gravitational theory according to Einstein

Okay.. that goes way over my head. I am a mathematician, not a physics graduate.

If you are interested vsauce has a popsci video on that:

What is gravity on a flat earth?

Nobody really knows, same as the globe earthers. As far as I can tell there are no conclusive models, models we could test.

There are a few theories: 

One is that it is all caused by buoyancy or density, another is that the earth is accelerating as 9.81 m/s2. Or finally that there is a force all around us, pulling us down.

Density & buoyancy


Universal Accelaration

This wiki says: "According to Flat Earth Theory, gravity is not the main force keeping us on the ground. Instead, there is a force that produces identical effects as observed from the surface of the earth. This force is known as "Universal Acceleration" (abbreviated as UA).

Objects on the earth's surface have weight because all sufficiently massive celestial bodies are accelerating upward at the rate of 9.8 m/s^2. The mass of the earth is thought to shield the objects atop it from the direct force of UA. Alternatively, it is possible that the force of UA can actually pass through objects, but its effect on smaller bodies is negligible (similar to gravity in RET cosmology, which only has a noticeable affect on very large objects)."

The Davis model

The Davis model, suggested by John Davis, states that gravity does indeed exist. In this model, the Earth is an infinite disk with finite gravity.


My thoughts on this

In a usual flat model (the limited flatearth disc) Einstein's gravity cannot exist, because the earth would have pulled itself into a ball, or the direction of the gravity pull would not be downwards, but relative to the centre of the flat plane.

The density theory is a description of what we see: A helium balloon flies away and a stone drops. However it does not explain why the direction is downward/upward. This is usually taken as a given, but that is too easy. Dismissing that question is exactly what should not be done.

The universal acceleration theory does account for a downward force. However is does not explain the differences that can be measured on the different parts of the earth.
Also it would mean that the earth, and all other object that we can see in the sky, are not only flying through space but actually speeding up. This would require an immense power source and imagine the speeds we would be going right now.

The Davis model shows a theory of a downward force, more or less equally spread across, or under, the earth. What this force is, is hard to tell, but Newton and Einstein and all the others did not reach their conclusions after just a few years.

As long as there is no consistent model that can be used and tested and gives an explanation of the how of the forces involved, on this the flatearth model is flawed.
As to the why, what causes gravity, the models have a long way to go.

And a model is only valid until someone proofs the contrary. All examples shown fail to do that with regards to the Einstein model.

Density and buoyancy are sometimes considered an alternative for the presence of gravity.

The theory behind this is that objects that are denser than other objects will move down. So a solid object, which is denser than air, will fall to the ground. Less dense material (oil) will float on denser material (like water). Like in the video below.

This is true. You can see it all around you. And what the theory describes is perfectly in line with a gravitational model.
What the model however does not explain is how the objects have a direction. Why does an apple fall to the ground and not go sideways. And why would, in a vacuum, objects (like the classic ball/feather experiment) move at all? There must be a force action upon it, the objects actually accelerate towards a certain direction.

This force is pointed downwards in the medium we live in. But you can do other experiments to see the effect of density differences. Any laboratory know how to separate denser material from less denser material by using centrifugation. The effects are identical to what you might expect due to gravity, only the force (centrifugal) gives it an other direction.

Or how can we float in the air at zero G (like in a plane in a hyperbolic curve). Is the density of the air suddenly changed because we are falling?

The theory behind buoyancy is completely explained by the rules defined by the gravity theory. You can predict exactly what will happen in the different environment.

Below is a good video of the principles involved. Also there is a nice experiment where bubbles are enclosed in a bottle of water. Off course the air rises to the top of the bottle. However when the bottle is dropped, the bubbles do not rise any more, within there own environment. So does falling to the ground suddenly changes the density of water?