Why would Earth move in straight line without sun's gravity?

[avito009]

If there was no Sun then the Earth would move in a straight line with constant velocity. This is because the space has vacuum and there is no friction in space. This is because if you observe on Earth where there is friction we need to apply force against this friction. But in space there is vacuum and no friction.

Am I right?

 

[Vagn]

If there was no Sun then the Earth would move in a straight line with constant velocity. This is because the space has vacuum and there is no friction in space. This is because if you observe on Earth where there is friction we need to apply force against this friction. But in space there is vacuum and no friction.

Am I right?

The momentum of the Earth would have to be conserved. The Earth's motion still wouldn't be perfectly straight though, as there are still gravitational effects due to the moon, and the other planets. The Earth would also still continue to orbit the galactic centre. 'Linear' would depend on your scale.

 

[Nugatory]

Am I right?

Pretty much, yes. This is an application of Newton's first law.

 

[Drakkith]

The existence of friction makes us have to apply a force just to keep moving. It has nothing to do with moving in a straight line or not. An object will move in a straight line if there is no force pushing/pulling it in another direction. I can slide a box across a flat piece of concrete and the box will move in a straight line after I let go even though it is slowing down because of friction.

Earth moves with a (near) constant velocity in space because there is (almost) no friction. But it certainly doesn't move in a straight line as it orbits the Sun.