# The Naked Scientists Forum

### Author Topic: Propellant at the speed of light  (Read 3284 times)

#### VictorEliasEspinozaGuedez

• Sr. Member
• Posts: 131
##### Propellant at the speed of light
« on: 10/10/2014 15:46:11 »

#### RD

• Neilep Level Member
• Posts: 8125
• Thanked: 53 times
##### Re: Propellant at the speed of light
« Reply #1 on: 10/10/2014 17:32:08 »
Ignoring air resistance, the projectile would have to reach Earth's escape velocity, (11km/s), as it left the end of the barrel.  The acceleration from rest to 11km/s over the length of the gun-barrel would be astronomically high : anyone in the projectile would be completely obliterated because of the [g]force associated with that acceleration.

http://en.wikipedia.org/wiki/Space_gun
« Last Edit: 10/10/2014 17:38:40 by RD »

#### VictorEliasEspinozaGuedez

• Sr. Member
• Posts: 131
##### Re: Propellant at the speed of light
« Reply #2 on: 10/10/2014 19:35:45 »
Ignoring air resistance, the projectile would have to reach Earth's escape velocity, (11km/s), as it left the end of the barrel.  The acceleration from rest to 11km/s over the length of the gun-barrel would be astronomically high : anyone in the projectile would be completely obliterated because of the [g]force associated with that acceleration.

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

A question: Time to get to Mars?

a. Escape velocity, which is 11.2 km/s on Earth

b. The acceleration (a) would theoretically be more than 1000 m/s2

c. Distance: 78.300.000 Km

http://en.wikipedia.org/wiki/Space_gun
« Last Edit: 10/10/2014 20:09:02 by VictorEliasEspinozaGuedez »

#### RD

• Neilep Level Member
• Posts: 8125
• Thanked: 53 times
##### Re: Propellant at the speed of light
« Reply #3 on: 10/10/2014 20:25:47 »
a. Escape velocity, which is 11.2 km/s on Earth

b. The acceleration (a) would theoretically be more than 1000 m/s2

The acceleration would depend on how long the barrel of the gun was,
even if the barrel was a kilometre long the acceleration would be about 50,000m/s2 : The people inside the projectile would be subject to a force 5000x their weight on Earth., ( i.e. squashed like a cockroach underfoot ).

[ this calculation does not include air resistance, in air the force required would be greater ]
« Last Edit: 10/10/2014 20:49:33 by RD »

#### VictorEliasEspinozaGuedez

• Sr. Member
• Posts: 131
##### Re: Propellant at the speed of light
« Reply #4 on: 10/10/2014 21:03:22 »
A question: Time to get to Mars?

a. Escape velocity, which is 11.2 km/s on Earth

b. The acceleration (a) would theoretically be more than 1000 m/s2

c. Distance: 78.300.000 Km

d. Starting point: orbit of the planet Earth

e. Arrival point: orbit of the planet Mars

f. Time = ?

#### VictorEliasEspinozaGuedez

• Sr. Member
• Posts: 131
##### Re: Propellant at the speed of light
« Reply #5 on: 10/10/2014 21:48:58 »
a. Escape velocity, which is 11.2 km/s on Earth

b. The acceleration (a) would theoretically be more than 1000 m/s2

The acceleration would depend on how long the barrel of the gun was,
even if the barrel was a kilometre long the acceleration would be about 50,000m/s2 : The people inside the projectile would be subject to a force 5000x their weight on Earth., ( i.e. squashed like a cockroach underfoot ).

[ this calculation does not include air resistance, in air the force required would be greater ]

..."i.e. squashed like a cockroach underfoot"

The pressure inside the spaceship is that crushes it.
The Astronaut carries the same speed of the spacecraft.
With a front pressure protector. The pressure to crush the astronaut must be avoided.

#### RD

• Neilep Level Member
• Posts: 8125
• Thanked: 53 times
##### Re: Propellant at the speed of light
« Reply #6 on: 10/10/2014 23:10:32 »
..."i.e. squashed like a cockroach underfoot"

The pressure inside the spaceship is that crushes it.

Acceleration creates the force , air-pressure is not required : force due to acceleration exists in a vacuum.

The Astronaut carries the same speed of the spacecraft.

Before the gun is fired the projectile is at rest : 0km/s,
at the end of the barrel it must be in excess of 11km/s.
If the barrel is one kilometre long the projectile has accelerated from 0 to 40,000km/h in about 0.2 seconds => ~5000g => "astronauts" squashed flat before the projectile has left the barrel of the gun.
« Last Edit: 10/10/2014 23:17:11 by RD »

#### VictorEliasEspinozaGuedez

• Sr. Member
• Posts: 131
##### Re: Propellant at the speed of light
« Reply #7 on: 11/10/2014 00:12:55 »
..."i.e. squashed like a cockroach underfoot"

The pressure inside the spaceship is that crushes it.

Acceleration creates the force , air-pressure is not required : force due to acceleration exists in a vacuum.

The Astronaut carries the same speed of the spacecraft.

Before the gun is fired the projectile is at rest : 0km/s,
at the end of the barrel it must be in excess of 11km/s.
If the barrel is one kilometre long the projectile has accelerated from 0 to 40,000km/h in about 0.2 seconds => ~5000g => "astronauts" squashed flat before the projectile has left the barrel of the gun.

The astronaut who crushes? The air inside the space shuttle? What you need to do, is to protect the astronaut, of the air inside the spaceship. Because the air is not moving.

#### RD

• Neilep Level Member
• Posts: 8125
• Thanked: 53 times
##### Re: Propellant at the speed of light
« Reply #8 on: 11/10/2014 04:57:09 »
The astronaut who crushes? The air inside the space shuttle? What you need to do, is to protect the astronaut, of the air inside the spaceship. Because the air is not moving.

Air is not necessary to transmit the g-forces due to acceleration.

Here is a YouTube of pilots at 5g ...
[ what would 5000g be like ?  [xx(] ]
« Last Edit: 11/10/2014 04:59:39 by RD »

#### VictorEliasEspinozaGuedez

• Sr. Member
• Posts: 131
##### Re: Propellant at the speed of light
« Reply #9 on: 11/10/2014 05:15:46 »
The astronaut who crushes? The air inside the space shuttle? What you need to do, is to protect the astronaut, of the air inside the spaceship. Because the air is not moving.

Air is not necessary to transmit the g-forces due to acceleration.

Here is a YouTube of pilots at 5g ...
[ what would 5000g be like ?  [xx(] ]

How gravity crushes the astronaut?
The astronaut is going at the same speed of the spacecraft. What gravity?
Yes the spaceship It is a vacuum nothing crushes it.
« Last Edit: 11/10/2014 05:27:41 by VictorEliasEspinozaGuedez »

#### RD

• Neilep Level Member
• Posts: 8125
• Thanked: 53 times
##### Re: Propellant at the speed of light
« Reply #10 on: 11/10/2014 05:32:38 »
How gravity crushes the astronaut?

Force of acceleration crushes the astronaut.
Force can be expressed in a unit equal to Earth's gravity "g".
A force of 5000g would be about the same as a stack of ten buses on top of the person.

#### VictorEliasEspinozaGuedez

• Sr. Member
• Posts: 131
##### Re: Propellant at the speed of light
« Reply #11 on: 11/10/2014 05:50:47 »
How gravity crushes the astronaut?

Force of acceleration crushes the astronaut.
Force can be expressed in a unit equal to Earth's gravity "g".
A force of 5000g would be about the same as a stack of ten buses on top of the person.

both the spacecraft and astronaut have the same speed and acceleration.
And what crushes the astronaut, if the ship is vacuum in the inside?
« Last Edit: 11/10/2014 05:58:24 by VictorEliasEspinozaGuedez »

#### RD

• Neilep Level Member
• Posts: 8125
• Thanked: 53 times
##### Re: Propellant at the speed of light
« Reply #12 on: 11/10/2014 09:04:35 »
... what crushes the astronaut, if the ship is vacuum in the inside?

The part of the accelerating "ship" they are in contact with , (a chair , a wall ) , applies the force to their body.
« Last Edit: 11/10/2014 09:06:49 by RD »

#### PmbPhy

• Neilep Level Member
• Posts: 2760
• Thanked: 38 times
##### Re: Propellant at the speed of light
« Reply #13 on: 11/10/2014 11:00:18 »
Quote from: VictorEliasEspinozaGuedez
both the spacecraft and astronaut have the same speed and acceleration.
And what crushes the astronaut, if the ship is vacuum in the inside?
The astronaut is crushed **because** the spacecraft and astronaut have the same speed and acceleration. Before the spacecraft starts to accelerate the astronaut is not compressed. When the spacecraft starts to accelerate the astronaut, wanting to remain at rest due to its inertia, will not all accelerate at once. The part nearest the spacecraft will start moving while the opposite end stays at rest. As time goes on the accelerating spacecraft compresses the astronaut until all parts have the same acceleration. When that happens all parts have the same speed and acceleration and the astronaut remains in a compressed state.

Think about what happens to a very long spring when you push on one end if it? Does the entire spring move all at once uncompressed or does it compress before it all moves with the same speed? Think of the astronaut as a spring.

#### VictorEliasEspinozaGuedez

• Sr. Member
• Posts: 131
##### Re: Propellant at the speed of light
« Reply #14 on: 11/10/2014 15:34:17 »
... what crushes the astronaut, if the ship is vacuum in the inside?

The part of the accelerating "ship" they are in contact with , (a chair , a wall ) , applies the force to their body.

What wall? Of what is made

#### VictorEliasEspinozaGuedez

• Sr. Member
• Posts: 131
##### Re: Propellant at the speed of light
« Reply #15 on: 11/10/2014 15:41:24 »
Quote from: VictorEliasEspinozaGuedez
both the spacecraft and astronaut have the same speed and acceleration.
And what crushes the astronaut, if the ship is vacuum in the inside?
The astronaut is crushed **because** the spacecraft and astronaut have the same speed and acceleration. Before the spacecraft starts to accelerate the astronaut is not compressed. When the spacecraft starts to accelerate the astronaut, wanting to remain at rest due to its inertia, will not all accelerate at once. The part nearest the spacecraft will start moving while the opposite end stays at rest. As time goes on the accelerating spacecraft compresses the astronaut until all parts have the same acceleration. When that happens all parts have the same speed and acceleration and the astronaut remains in a compressed state.

Think about what happens to a very long spring when you push on one end if it? Does the entire spring move all at once uncompressed or does it compress before it all moves with the same speed? Think of the astronaut as a spring.

And what compresses a spring?

#### The Naked Scientists Forum

##### Re: Propellant at the speed of light
« Reply #15 on: 11/10/2014 15:41:24 »

Login
Login with username, password and session length