# Gravity and curvature of space

1. Aug 27, 2011

### rajeshmarndi

I could understand gravity involve in object revolving around a big mass as the path of the object is circular.

But couldn't understand how gravity is explained when an object thrown up returns back.

2. Aug 27, 2011

### tiny-tim

hi rajeshmarndi!

are you also happy about an orbit where the path is elliptical?

when you throw an object almost vertically, it follows an arc of an ellipse until it hits the ground …

if the ground wasn't there, it would orbit in that ellipse forever​

when you throw an object exactly vertically, if the ground wasn't there, it would go up and down forever in a "flat ellipse"

3. Aug 27, 2011

### A.T.

Geodesic path in curved spacetime for a vertical throw.
http://www.relativitet.se/spacetime1.html

4. Aug 27, 2011

### rajeshmarndi

thanks A.T, for providing the link also.
It was helpful what i was searching.

5. Aug 27, 2011

### A.T.

Here is an interactive version of that, where you can thow it up and let it fall into a tunnel through the planet:

6. Aug 27, 2011

### Naty1

A convenient way to remember how gravitational acceleration looks in spacetime is, which summarizes some detailed mathematics, is (with time on one axis and space on two others):

constant velocity appears as a straight line,

constant linear acceleration appears as a smooth curve, (say. an freely falling object)

constant rotational acceleration appears as a corkscrew (say, the earth rotating about the sun)

7. Aug 28, 2011

### rajeshmarndi

AT -

thanks again, its really a new way users like me to have a look at space-time curve.

8. Aug 28, 2011

### A.T.

The title of the thread suggests that you might have had the misconception that it's the curvature of space only, that models gravity in General Relativity. But in fact the time dimension is crucial to understand the key effect of gravity: mass attraction.

Have a look at this:
http://www.physics.ucla.edu/demoweb..._and_general_relativity/curved_spacetime.html

9. Aug 28, 2011

### jishitha

I guess, that is acceleration due to gravity.When an object is thrown vertically up then,it come down it caused gravity . Gravity always attractive. And it always directed to the earth.

10. Aug 29, 2011

### kyrdmenchou

i could not understan about this given problem.. " A car travels up a nill at a constant speed of 37 km/h & return down the hill at a constat speed of 66 km/h. Calculate the average speed for the whole trip."
Can somebody help me answer this?,,, thaks a lot...

11. Aug 29, 2011

### HallsofIvy

Staff Emeritus
The last two posts seem to have missed the point completely- that this is about the General Relativity picture of gravity.