# Can someone calculate time neede to accelerate to light speed for me? **URL:** \ **Category:** Factual Questions\ **Created:** [July 5, 2003, 3:00am UTC](https://boards.straightdope.com/t/can-someone-calculate-time-neede-to-accelerate-to-light-speed-for-me/186334 "2003-07-05T03:00:27Z")\ **Posts on this page:** 16\ **Page:** 3
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [July 6, 2003, 2:07pm UTC](https://boards.straightdope.com/t/can-someone-calculate-time-neede-to-accelerate-to-light-speed-for-me/186334/41 "2003-07-06T14:07:16Z")
> [@](#): > > \*Originally posted by Ring \* > The only reason I used the one I did is because a lot of peoples eyes tend to glaze over when they see hyperbolic functions. I think you are being a bit hyperbolic there. 😉 ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [July 6, 2003, 2:36pm UTC](https://boards.straightdope.com/t/can-someone-calculate-time-neede-to-accelerate-to-light-speed-for-me/186334/42 "2003-07-06T14:36:59Z")
> [@](#): > > \*Originally posted by Whack-a-Mole \* > \*\*Good point…stationary observer I think as that would be the longer time. As perceived aboard the spaceship it’d be shorter but I don’t think it’d be all that much. IIRC time dilation only really becomes serious above .85 or .9 c. It exists before that but the dilation is so small that I think it can be safely ignored. \*\* It also makes a difference whether you want the 1 g acceleration to be from the stationary perspective, or the onboard perspective. Probably, you’d want 1 g acceleration for those on board, to simulate Earth gravity, but that’s different from the stationary observer seeing 1 g acceleration. If the stationary observer sees the ship accelerating at 1 g, it’ll see the ship get up to light speed in about a year (hypothetically, since a ship would never get to light speed). Of course, the onboard observers would experience a shorter time, but they’d also experience higher and higher levels of gravity. If the onboard observer experienced a constant acceleration, the stationary observer would see it gradually reducing its acceleration, never reaching light speed. ---
**Author:** ![KidCharlemagne](https://avatars.discourse-cdn.com/v4/letter/k/ed8c4c/32.png) [@KidCharlemagne](https://boards.straightdope.com/u/KidCharlemagne)\ **Post date:** [July 6, 2003, 4:10pm UTC](https://boards.straightdope.com/t/can-someone-calculate-time-neede-to-accelerate-to-light-speed-for-me/186334/43 "2003-07-06T16:10:17Z")
Related question: Is 1g terminal velocity on earth? 120ft/sec^2? ---
**Author:** ![av8rmike](https://avatars.discourse-cdn.com/v4/letter/a/edb3f5/32.png) [@av8rmike](https://boards.straightdope.com/u/av8rmike)\ **Post date:** [July 6, 2003, 5:43pm UTC](https://boards.straightdope.com/t/can-someone-calculate-time-neede-to-accelerate-to-light-speed-for-me/186334/44 "2003-07-06T17:43:25Z")
> [@](#): > > Is 1g terminal velocity on earth? 120ft/sec^2? Quick answer: no. Longer answer: Terminal velocity is defined as the balance between the gravitational and drag forces. Drag of a body is based on many factors, including shape (cross-sectional area). So you falling with a parachute, without a parachute, and a sphere will all have different terminal velocities. ---
**Author:** ![Terminus\_Est](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/terminus_est/32/3087_2.png) [@Terminus\_Est](https://boards.straightdope.com/u/Terminus_Est)\ **Post date:** [July 6, 2003, 5:45pm UTC](https://boards.straightdope.com/t/can-someone-calculate-time-neede-to-accelerate-to-light-speed-for-me/186334/45 "2003-07-06T17:45:51Z")
The correct answer: 1g is not a velocity, it is acceleration due to gravity. ---
**Author:** ![Sam\_Stone](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Sam\_Stone](https://boards.straightdope.com/u/Sam_Stone)\ **Post date:** [July 6, 2003, 6:16pm UTC](https://boards.straightdope.com/t/can-someone-calculate-time-neede-to-accelerate-to-light-speed-for-me/186334/46 "2003-07-06T18:16:24Z")
Absent an atmosphere, the gravitational acceleration of a falling body on the Earth is 32.2 ft/sec^2. In the real world, you will accelerate until the force due to aerodynamic drag exactly balances out the gravitational force. Once you’re in equilibrium, you’re at terminal velocity, and there you’ll stay until something changes (your shape, air density), or until there’s a big SPLAT. ---
**Author:** ![KidCharlemagne](https://avatars.discourse-cdn.com/v4/letter/k/ed8c4c/32.png) [@KidCharlemagne](https://boards.straightdope.com/u/KidCharlemagne)\ **Post date:** [July 6, 2003, 10:28pm UTC](https://boards.straightdope.com/t/can-someone-calculate-time-neede-to-accelerate-to-light-speed-for-me/186334/47 "2003-07-06T22:28:07Z")
> [@](#): > > \*Originally posted by Sam Stone \* > \*\*Absent an atmosphere, the gravitational acceleration of a falling body on the Earth is 32.2 ft/sec^2. > > In the real world, you will accelerate until the force due to aerodynamic drag exactly balances out the gravitational force. Once you’re in equilibrium, you’re at terminal velocity, and there you’ll stay until something changes (your shape, air density), or until there’s a big SPLAT. \*\* Whoops I meant 32 ft/sec^2. IIRC terminal velocity is 120 ft/sec. So then is 1g acceleration 32ft/sec^2? ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [July 6, 2003, 10:31pm UTC](https://boards.straightdope.com/t/can-someone-calculate-time-neede-to-accelerate-to-light-speed-for-me/186334/48 "2003-07-06T22:31:51Z")
> [@](#): > > \*Originally posted by KidCharlemagne \* > \*\*Whoops I meant 32 ft/sec^2. IIRC terminal velocity is 120 ft/sec. So then is 1g acceleration 32ft/sec^2? \*\* Yes, 1 g = 32 ft/s[sup]2[/sup] or 9.8 m/s[sup]2[/sup]. As previously stated, V[sub]terminal[/sub] depends on a number of factors, including surface-to-volume ratio, density, shape, etc. It’s about 120 ft/s for the average solo skydiver. ---
**Author:** ![KidCharlemagne](https://avatars.discourse-cdn.com/v4/letter/k/ed8c4c/32.png) [@KidCharlemagne](https://boards.straightdope.com/u/KidCharlemagne)\ **Post date:** [July 6, 2003, 11:04pm UTC](https://boards.straightdope.com/t/can-someone-calculate-time-neede-to-accelerate-to-light-speed-for-me/186334/49 "2003-07-06T23:04:00Z")
Ok, I thought 120ft/s was in a vacuum. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [July 6, 2003, 11:08pm UTC](https://boards.straightdope.com/t/can-someone-calculate-time-neede-to-accelerate-to-light-speed-for-me/186334/50 "2003-07-06T23:08:22Z")
No, in a vacuum an object can fall at any velocity up to the escape velocity of the body it is falling towards. On Earth that would be 7 mi./s (36,960 ft/s). ---
**Author:** ![KidCharlemagne](https://avatars.discourse-cdn.com/v4/letter/k/ed8c4c/32.png) [@KidCharlemagne](https://boards.straightdope.com/u/KidCharlemagne)\ **Post date:** [July 6, 2003, 11:24pm UTC](https://boards.straightdope.com/t/can-someone-calculate-time-neede-to-accelerate-to-light-speed-for-me/186334/51 "2003-07-06T23:24:38Z")
> [@](#): > > \*Originally posted by Q.E.D. \* > \*\*No, in a vacuum an object can fall at any velocity up to the escape velocity of the body it is falling towards. On Earth that would be 7 mi./s (36,960 ft/s). \*\* \ So an airplane can get to 30,000 or so ft. without going anywhere near that velocity because, although the gravitational attraction is greater closer to earth, there is a greater density to the atmosphere to push off from? ---
**Author:** ![Thaumaturge](https://avatars.discourse-cdn.com/v4/letter/t/858c86/32.png) [@Thaumaturge](https://boards.straightdope.com/u/Thaumaturge)\ **Post date:** [July 7, 2003, 12:49am UTC](https://boards.straightdope.com/t/can-someone-calculate-time-neede-to-accelerate-to-light-speed-for-me/186334/52 "2003-07-07T00:49:04Z")
Airplanes fly because of the interaction of the wings with the air. The escape velocity of the earth has little to do with it. ---
**Author:** ![Thaumaturge](https://avatars.discourse-cdn.com/v4/letter/t/858c86/32.png) [@Thaumaturge](https://boards.straightdope.com/u/Thaumaturge)\ **Post date:** [July 7, 2003, 12:51am UTC](https://boards.straightdope.com/t/can-someone-calculate-time-neede-to-accelerate-to-light-speed-for-me/186334/53 "2003-07-07T00:51:16Z")
> [@](#): > > \*Originally posted by Whack-a-Mole \* > \*\*I assume you are asking if anything can be considered at rest. E.G. a rock somewhere with an inscription that says, “This Rock Is Not Moving –_God_” > > The real answer is no…there is no absolute speed (which zero would be) to benchmark other speeds against. \*\* How about an object that had zero redshift to the cosmic microwave background radiation in all directions? ---
**Author:** ![KidCharlemagne](https://avatars.discourse-cdn.com/v4/letter/k/ed8c4c/32.png) [@KidCharlemagne](https://boards.straightdope.com/u/KidCharlemagne)\ **Post date:** [July 7, 2003, 1:31am UTC](https://boards.straightdope.com/t/can-someone-calculate-time-neede-to-accelerate-to-light-speed-for-me/186334/54 "2003-07-07T01:31:08Z")
> [@](#): > > \*Originally posted by Thaumaturge \* > \*\*Airplanes fly because of the interaction of the wings with the air. The escape velocity of the earth has little to do with it. \*\* I think that was the point of my question. The reason you don’t have to worry about escape velocity with airplanes is because you do have air in the lower atmosphere. Just because the force is lift and not thrust doesn’t change the fact that gravity is the force being contended with, right? I guess my question is, at what point does the lack of air to provide lift become countered by gravity( less whatever thrust the engines provide regardless of lift) so that an airplane can’t go any higher? Or perhaps a simpler wording would be, “How high can a DC10 fly?” ---
**Author:** ![KidCharlemagne](https://avatars.discourse-cdn.com/v4/letter/k/ed8c4c/32.png) [@KidCharlemagne](https://boards.straightdope.com/u/KidCharlemagne)\ **Post date:** [July 7, 2003, 1:43am UTC](https://boards.straightdope.com/t/can-someone-calculate-time-neede-to-accelerate-to-light-speed-for-me/186334/55 "2003-07-07T01:43:16Z")
Ok I just read a little about escape velocity and I see that it’s the velocity without further need of propulsion. Got it. But I still want to know how high a DC10 can fly. ---
**Author:** ![av8rmike](https://avatars.discourse-cdn.com/v4/letter/a/edb3f5/32.png) [@av8rmike](https://boards.straightdope.com/u/av8rmike)\ **Post date:** [July 7, 2003, 2:53am UTC](https://boards.straightdope.com/t/can-someone-calculate-time-neede-to-accelerate-to-light-speed-for-me/186334/56 "2003-07-07T02:53:58Z")
The service ceiling of an aircraft is that altitude at which the wings can no longer provide lift while the aircraft is in equilibrium (because of the decreasing air density). [This site](http://www.aerospaceweb.org/aircraft/jetliner/dc10/) lists the ceiling of a DC10 at 33,400 feet. More modern airliners can cruise at 37,000 feet or higher, while bizjets can operate at 41,000 feet or so. [Previous page](https://boards.straightdope.com/t/can-someone-calculate-time-neede-to-accelerate-to-light-speed-for-me/186334.md?page=2)