# B What is the evidence that there is gravitation?

1. Feb 19, 2017

### Intikam the ruthless

Hi guys. I hope Scientists are at the same time civilized. Because science is civilization.

Firstly I'm sorry about language. In Turkey, Our education system does not adequately support English. Anyway.

What is the evidence about gravity is exist. Wait. I mean, we know something pushing everything down or pulling everything down, we know it. But why do we think that something is a force and why it should be gravity?

Do you have a scientific explanation before you are far from science? Or do you just believe that?

2. Feb 19, 2017

### cnh1995

Because it accelerates mass. Drop a stone from certain height and it will accelerate on its way down. Throw a stone up in the air and it will decelerate (then stop and fall back on the ground) instead of going into outer space. There is an entire chapter on gravitation in every physics book, with mathematics to prove everything stated.

I am not sure what you are trying to say in this post.

3. Feb 19, 2017

### Staff: Mentor

Why do we know there is a force? Because we observe it effects.

Why do we call it gravity? Because that's the name we have chosen for this particular force that presents itself between any two masses.

4. Feb 19, 2017

### Staff: Mentor

It depends on the theory that we use to describe it. In classical Newtonian physics, the force that causes an apple to fall to the ground is a force similar to other forces, which is calculated from Newton's law of gravitation. In Einstein's general relativity, the falling apple does not experience a "gravitational force"; its motion with respect to the ground is caused by the curvature of spacetime. The apple itself does not "feel" any force. Nor do we "feel" any gravitational force if we are inside a freely falling elevator.

5. Feb 19, 2017

### Mmm_Pasta

That "something" we see, we simply label it as a force that we call gravity. This "thing" we call a force, with the name gravity, has certain properties and it explains a large amount of phenomenon that we see around us. Otherwise, we'll be going into an argument about semantics if I'm understanding the content in your post correctly. In other words: why do we call those tall brown-stemmed green foliage wonders "trees" and not "pillows"?

6. Feb 19, 2017

### Intikam the ruthless

I still haven't get the answer what I search for. We know there is a force but what is the evidence it caused by a mass Gravity.

For be more understandable, I want to say it clearly for this time:

Is there an experiment in space (or in vakuum environment) where the masses mutually attracted and the mass constant is confirmed. What is the scientific explanation and calculation of the masses pulling each other? Please just come up with scientific explanations.

7. Feb 20, 2017

### cnh1995

8. Feb 20, 2017

### Drakkith

Staff Emeritus
Newtonian gravitation is described in the following article, which includes the basic calculation for the force between two masses.
https://en.wikipedia.org/wiki/Newton's_law_of_universal_gravitation#Modern_form

The masses of objects can be measured and the force of gravity on/from these masses can then be measured and compared to a calculation involving Newton's law of gravitation. An extensive number of experiments have been done and the results support our theories. There is an immense amount of evidence supporting the idea that gravity is caused by mass.

9. Feb 20, 2017

### Staff: Mentor

Yes. For small objects close to one another there are experiments like the Cavendish and Eotvos experiments (google for more information). For large objects far away from one another, we observe the acceleration of the planets (which are large objects in a vacuum), calculate the force needed to produce these accelerations, and find that that force is what is predicted for the force of gravity.

Every time that we launch a spacecraft on a trajectory that puts it in a particular orbit or sends it to another planet, and every time that we aim and fire a large artillery piece, we're depending on calculations that assume there is a gravitational force and that we have the right mass constant. If these assumptions were not correct, we'd know about it.

10. Feb 20, 2017

### Staff: Mentor

In other words: each time we use these calculations we are actually testing the theory.

11. Feb 20, 2017

### CWatters

Good theories frequently lead to testable predictions. Read up on the history of gravity and how Newton came up with a theory that allowed the existence of then unknown planets to be predicted. Then read on to discover that the motion of some planets proved Newton wasn't the whole story.

12. Feb 20, 2017

### ZapperZ

Staff Emeritus
You are dismissing the quantitative aspect of science.

Please note that physics just doesn't say "what goes up, must come down", which is what you are asking for here. It must also say "when and where it comes down"!

The Newtonian gravity has been verified quantitatively. In other words, we have gone WAY past showing that mass causes gravity. We have gone into predicting and quantifying the strength of gravity and how they behave as we change position, location, masses, etc. It is how we can predict celestial movement, etc. Nothing shows that you have and understanding of something better than making quantitative predictions and matching those to actual measurements.

You are still thinking that we need to "prove" mass causes gravity. That's child's play!

Zz.

13. Feb 20, 2017

### Staff: Mentor

A version of the Cavendish experiment is often done in undergraduate laboratory classes nowadays, and some companies offer specialized apparatus to make it easy to set up and perform, for example this one.

14. Feb 25, 2017

### Staff: Mentor

Time to close this thread as we have adequately explained the nature of gravity to the OP.

I'd like to thank all who posted here whether or not you see your post.

Closing now.