# Thread: Newtons 1st Law of motion in a vacuum

1. ## Newtons 1st Law of motion in a vacuum

Hi I was wondering what happens to a car accelerating in a vacuum? Outside a vacuum, cars will attain a constant speed due to air resistance eventually equalling the traction force. So, will Newtons 1st law negate in a vacuum? Since their is no air resistance, will a car built to 120mph exceed that speed? Just my mind meandering. Tell me what you think.

2. A car can probably go faster in a vacuum than not, but there will still be many other frictional forces at work, including rolling friction, friction between the axle and the bearings, etc. There will still be a "terminal velocity", so to speak.

3. [QUOTE=Ackbeet;606697]A car can probably go faster in a vacuum than not, but there will still be many other frictional forces at work, including rolling friction, friction between the axle and the bearings, etc. There will still be a "terminal velocity", so to speak.[/QUOTE
So, in essence, there will always be limitations to achieving maximum speed? Does this situation exist for outer space? Also, Whats possible forces can provide effective resistance to objects travelling at the speed of light? I am wondering if the high speed creates a measure of frictional force in its relative motions.

4. In space, there will be even fewer limitations, but you'll certainly run into practical limitations, such as limited fuel for your rockets (about the only way to propel yourself in space, aside from the "solar sail" we hear so much about). Space is a near-vacuum, so you'll still have collisions with molecules and atoms (albeit very few) slowing you down.

It's not so much that there are a bunch of forces preventing you from achieving speeds near that of light: it's a question of practicality, and the sheer amount of energy required to accelerate anything to that speed. Just look at the Large Hadron Collider, and how much energy it uses to accelerate just a few particles to something like 0.999999991 c, or about 3 m/s slower than the speed of light. So the main forces preventing effective resistance to objects traveling at the speed of light are monetary and practical!

Incidentally, Newton's first law is still valid even in vacuum.