Acceleration in Space

the_syco

Quick question: as there is no gravity in space, would you still feel exceleration , in terms of G-Forces, if going at a high speed in space?

Spear

the_syco wrote: »

Quick question: as there is no gravity in space, would you still feel exceleration , in terms of G-Forces, if going at a high speed in space?

Time to read this then which deals with exactly that.

http://en.wikipedia.org/wiki/Equivalence_principle

Hoovers

the_syco wrote: »

Quick question: as there is no gravity in space, would you still feel exceleration , in terms of G-Forces, if going at a high speed in space?

In short, you would feel G-Forces in space as long as you were accelerating.
Say you were in a rocket, accelerating at some rate, then you would feel a G-Force pushing you back into your seat. When you reached constant speed the G-Forces would stop.

Kevster

Kind of related to this is something that annoys me a bit, and it's the way that the media always give the speed of satellites, spaceships, etc. when they are orbiting. They're only mentioning the high speeds to sensationalise the report. I mean, everything is relative in space. Therefore, two spacecraft orbiting at the exact same 'speed' would be like two spacecraft just lying stationary beside each other on Earth's surface - i.e. no real excitement or danger.

backboiler

the_syco wrote: »

Quick question: as there is no gravity in space, would you still feel exceleration , in terms of G-Forces, if going at a high speed in space?

G-forces are caused by acceleration, to which gravity can contribute but is not required. Mass is what matters and that doesn't change regardless of where you are. The confusion comes from the use of the "g" as a unit when speaking about G-forces , which is the acceleration due to gravity at the earth's surface, just under 10 m s^-2. If you experience a G-force of 6 g it means you feel 6 times as heavy as normal or, to put it in SI units, you're accelerating at about 60 m s^-2 in some direction.

Also there is gravity in space. Gravity acts on everything, falling off as the distance between objects increases but it doesn't suddenly stop. When you ascend above the Earth it's still pulling on you, just less than before, as is the sun and every planet and star you can see and all the other stuff you can't. Satellites in orbit are moving horizontally just fast enough so that the gravity of the Earth at their orbit height pulls them down towards the Earth's centre just enough to make them follow a squashed circular line. Exactly the same would happen if you could fire a bullet horizontally at great enough speed (ignoring air resistance) but speeds of orbiting craft relative to the Earth's surface are an order of magnitude faster than rifle bullets. If it's not going fast enough it drops to the ground, if it's going too fast it escapes the Earth and spirals off until something else's gravity causes its path to change.

You'll notice if you've ever seen a US space shuttle launch it kind of rolls over on its back a short time after take off and you hear of it being over Europe a few minutes later. It doesn't just fly straight up to some magic zero-gravity spot and take a right-hand turn. :P

Seanie M

Simple physics: velocity versus acceleration. Think of the last time you were on a (smooth) aeroplane journey. Acceleration on take-off puts you in your seat. When at 36,000 feet and cruising at a velocity of 420mph, you're free to get out of your seat and walk around.

Great practice for General Relativity too!

Seanie.

tricky D

backboiler wrote: »

The confusion comes from the use of the "G" as a unit when speaking about G-forces , which is the acceleration due to gravity at the earth's surface, just under 10 m s^-2.

You've got a bit confused yourself there

G is the gravitational constant (6.754 × 10−11 m3/kg/s2), g is acceleration due to gravity (in a vacuum, at sea level = 9.8 m/s2)

backboiler

tricky D wrote: »

You've got a bit confused yourself there

G is the gravitational constant (6.754 × 10−11 m3/kg/s2), g is acceleration due to gravity (in a vacuum, at sea level = 9.8 m/s2)

True enough, it should be lower case. I'll fix it above. Terrible mistake: discredits my whole response!