Does a so called space rocket accelerate?

Quote from: markjo on March 28, 2017, 03:18:51 PM

Why don't we start with you telling us your understanding of speed, velocity and acceleration?

Ok, speed is the distance covered in a time frame.
Velocity is speed in any given direction.
Acceleration Is a mixture of the two aforementioned.

Importantly, acceleration is the rate of change of speed.

So something can accelerate very slowly (i.e. constant, low acceleration) and still, in time, reach a very high speed.

If  car starts off at 10mph and builds it's speed every second up to 11 mph then 12 mph and never slowing and never staying at a constant speed, except always accelerating, then I expect a force to build up on a person driving that car and I expect that force to increase as the acceleration increases the mph.

If the acceleration remains constant, then the force won't increase. The force is dependent on the acceleration, not on the speed.

If I had an open top car with no windshield/screen and kept on accelerating, I'd expect to have my face stretched as the wind hits the skin at ever increasing friction as I drive into the atmosphere in front of me.

(This situation would be different as the wind effect is related to the speed.)

Quote from: Copper Knickers on March 28, 2017, 10:10:08 AM

You don't have to keep increasing your acceleration in order to keep increasing your speed.

Let's say you have a constant acceleration of 2g which is 19.6 m/s/s. Then:

After 1 second your speed will be 19.6 m/s.
After 2 seconds your speed will be 39.2 m/s.
After 3 seconds your speed will be 58.8 m/s.
...
After 7 minutes your speed will be 8232 m/s.

So the shuttle could reach its required speed in about 7 minutes without exceeding 2g.

That's what I mentioned.
What I don't get is the no change in g-force.

I don't agree with g-force to start with but for this particular conundrum, I fail to see how g-force stays constant with acceleration.

g-force is a measure of acceleration. So constant acceleration means constant g-force.

Importantly, acceleration is the rate of change of speed.

So something can accelerate very slowly (i.e. constant, low acceleration) and still, in time, reach a very high speed.

It doesn't matter how slowly. I already mentioned slowly accelerating.
The fact is the pressure build up would increase no matter how slowly. It would just increase slower than an obvious rapid acceleration.

If the acceleration remains constant, then the force won't increase. The force is dependent on the acceleration, not on the speed.

Acceleration cannot remain constant. It's impossible for acceleration to remain constant.
Unless I'm not understanding what acceleration means.
Constant means a situation that does not change. Acceleration changes or it wouldn't be acceleration.
Speed can be constant, so why is this dupe being put on people?

g-force is a measure of acceleration. So constant acceleration means constant g-force.

No, not at all.
Your g-force might be measured upon acceleration. A force certainly is, even though my real force is the reason.
Anyway, there cannot be constant acceleration, only constant speed.
This means that acceleration cannot create a constant g-force as you people abide by.

"constant acceleration"

Does sound like a contradiction 

change in speed or direction.
for example:
a car travelling at constant speed of 10kmh has an acceleration of 0...
a car travelling at 10kmh and with constant acceleration of 1m/s^2 will first go 10kmh for 1 second, then 11kmh for 2nd second then 12kmh for the 3th second and so on
a car travelling at 10kmh and with acceleration of 1m/s^2 and increasing acceleration of 1m/s^2 for every second, will first (A=1m/s^2) go 11kmh for 1 second then (A=2m/s^2) 13kmh for 2nd second then (A=3m/s^2) 16kmh for the 3th second, and so on.
so
constant:
a = 0, v =10kmh

constant acceleration:
second     speed     acceleration
0                 10             1
1                 11             1
2                 12             1
3                 13             1
4                 14             1
5                 15             1
6                 16             1

increasing acceleration:
second     speed     acceleration
0                 10             1
1                 11             2
2                 13             3
3                 16             4
4                 20             5
5                 25             6
6                 31             

as you can see in this last example, the acceleration is increasing and will build up more pressure on your body. you can also see that in this case, speed is not increasing linearly but exponentially.

as you can see in my post, there can be constant acceration.
A constant acceleration means that the spead increases linearly
if the acceleration increases linearly, the speed will increase exponently.
That is the main difference.

Acceleration cannot remain constant. It's impossible for acceleration to remain constant.
Unless I'm not understanding what acceleration means.
Constant means a situation that does not change. Acceleration changes or it wouldn't be acceleration.
Speed can be constant, so why is this dupe being put on people?

A linear acceleration of 4m/s² means that every second your velocity is increasing by 4m/s. This is constant acceleration. If you start at a velocity of 0m/s after 4 seconds you are traveling at a velocity of 16m/s.

Non-constant acceleration would be if in the first second your velocity increased by 5m/s but in the second second it increased by 7m/s and in the third it only increased by 3m/s and in the fourth it increased by 1m/s. It has taken you 4 seconds to reach a velocity of 16m/s but it wasn't constant acceleration.

Quote from: Copper Knickers on March 29, 2017, 12:47:25 AM

If the acceleration remains constant, then the force won't increase. The force is dependent on the acceleration, not on the speed.

Acceleration cannot remain constant. It's impossible for acceleration to remain constant.
Unless I'm not understanding what acceleration means.
Constant means a situation that does not change. Acceleration changes or it wouldn't be acceleration.
Speed can be constant, so why is this dupe being put on people?

Acceleration is rate of change of speed. That is, how quickly or slowly the speed is changing. If the speed changes by the same amount in equal time then the acceleration is said to be constant.

For instance I could accelerate my car at a constant acceleration of 5mph per second. Then after 1 second my speed would be 5mph, after 2 seconds it would be 10mph, and after 10 seconds it would be 50mph.

Although my speed has changed, the rate at which my speed is changing is still 5mph per second. This is what is meant by constant acceleration.

That's what I mentioned.
What I don't get is the no change in g-force.

I don't agree with g-force to start with but for this particular conundrum, I fail to see how g-force stays constant with acceleration.

Maybe it's just me not understanding just how magical this g-force is, eh?

The term "g-force" I believe was first applied to the acceleration felt by the crew of aircraft during fast manoeuvres, such as tight turns and the pull-out from a dive.

The "g-force" value is just how many times normal weight a crew member will feel.

It has also been applied to car acceleration and braking.
So saying a car is accelerating at "1-g" is the same as accelerating at 9.8 m/s² and "2-g" is the same as accelerating at 19.6 m/s².

You say "I fail to see how g-force stays constant with acceleration". The "g-force" does not "automatically stay constant".
For a car accelerating, the"g-force" is produced by the force the wheels apply to the road.
The driver controls this with the accelerator and gear selection.

Since force = mass x acceleration,
That's about the best I can do.

Dont be a dick Gumby.

Sorry?

Quote from: disputeone on March 28, 2017, 02:53:51 PM

Dont be a dick Gumby.

We all know Gumby is over compensating for something

Really? Can you please enlighten the forum?
It should be easy for you with all knowledge you got from your theological mechanics phd!

change in speed or direction.
for example:
a car travelling at constant speed of 10kmh has an acceleration of 0...

No problem, logically easy to accept.

a car travelling at 10kmh and with constant acceleration of 1m/s^2 will first go 10kmh for 1 second, then 11kmh for 2nd second then 12kmh for the 3th second and so on

Also no problem. It's easy to see how acceleration works.

a car travelling at 10kmh and with acceleration of 1m/s^2 and increasing acceleration of 1m/s^2 for every second, will first (A=1m/s^2) go 11kmh for 1 second then (A=2m/s^2) 13kmh for 2nd second then (A=3m/s^2) 16kmh for the 3th second, and so on.
so
constant:
a = 0, v =10kmh

There is no constant. It's a raise in speed and a raise in speed is acceleration which cannot ever be constant.

constant acceleration:
second     speed     acceleration
0                 10             1
1                 11             1
2                 12             1
3                 13             1
4                 14             1
5                 15             1
6                 16             1

increasing acceleration:
second     speed     acceleration
0                 10             1
1                 11             2
2                 13             3
3                 16             4
4                 20             5
5                 25             6
6                 31             

as you can see in this last example, the acceleration is increasing and will build up more pressure on your body. you can also see that in this case, speed is not increasing linearly but exponentially.

Why can't you people not see how silly this all is.
First you go with the logic and then decide to fall out of logic to take on something that makes no sense at all.
Constant acceleration is a nonsense.
Can't people see this?

Constant acceleration is far from nonsense. The gravity is at least for a given point on Earth a constant acceleration; 9.81 m/s^2.

Also napoleon's example shows how a constant acceleration of 1 km/h^2 works perfectly fine.

as you can see in my post, there can be constant acceration.

No there cannot be constant acceleration.
It's like saying the cops are chasing a robber who is constantly accelerating away from them when both are  at the same pace.
It makes no sense at all.

A constant acceleration means that the spead increases linearly

no. Acceleration is acceleration.
acceleration
əksɛləˈreɪʃ(ə)n/Submit
noun
a vehicle's capacity to gain speed.
"the three-litre model has spectacular acceleration"
synonyms:   speeding up, increasing speed, increase in speed, gain in momentum, gathering speed, opening up; technicalrate of change of velocity
"the car's acceleration is sensational"
increase in speed or rate.

Constant. noun
1.
a situation that does not change.

if the acceleration increases linearly, the speed will increase exponently.
That is the main difference.

Yes, if the acceleration increases, the speed will increase, obviously.
However, acceleration is an increase.
It cannot be constant.

Velocity goes from 0 metre per second to 1 meter per second in the first second.
Acceleration is 1 meter per second per second, velocity is 1 meter per second.

In the next second velocity goes to 2 meters per second.
Acceleration is still 1 meter per second per second , so it has stayed the same, but velocity is now 2 meters per second.

Acceleration is given in metres per second squared.
Velocity is metres per second.
They are not the same.

A linear acceleration of 4m/s² means that every second your velocity is increasing by 4m/s. This is constant acceleration. If you start at a velocity of 0m/s after 4 seconds you are traveling at a velocity of 16m/s.

The acceleration is fine but it is not constant at all.

Non-constant acceleration would be if in the first second your velocity increased by 5m/s but in the second second it increased by 7m/s and in the third it only increased by 3m/s and in the fourth it increased by 1m/s. It has taken you 4 seconds to reach a velocity of 16m/s but it wasn't constant acceleration.

It's no different. Neither are constant.
Your first one can be construed as consistent acceleration and your other can be construed as haphazard acceleration.

Neither are constant and can never be,in reality.

Acceleration is rate of change of speed. That is, how quickly or slowly the speed is changing. If the speed changes by the same amount in equal time then the acceleration is said to be constant.
For instance I could accelerate my car at a constant acceleration of 5mph per second. Then after 1 second my speed would be 5mph, after 2 seconds it would be 10mph, and after 10 seconds it would be 50mph.

Although my speed has changed, the rate at which my speed is changing is still 5mph per second. This is what is meant by constant acceleration.

The word you are looking for is, consistent. Constant cannot exist with acceleration no matter how it's dressed up.
It can only exist as fantasy science.

Quote from: Boots on March 29, 2017, 01:32:27 AM

A linear acceleration of 4m/s² means that every second your velocity is increasing by 4m/s. This is constant acceleration. If you start at a velocity of 0m/s after 4 seconds you are traveling at a velocity of 16m/s.

The acceleration is fine but it is not constant at all.

Quote from: Boots on March 29, 2017, 01:32:27 AM

Non-constant acceleration would be if in the first second your velocity increased by 5m/s but in the second second it increased by 7m/s and in the third it only increased by 3m/s and in the fourth it increased by 1m/s. It has taken you 4 seconds to reach a velocity of 16m/s but it wasn't constant acceleration.

It's no different. Neither are constant.
Your first one can be construed as consistent acceleration and your other can be construed as haphazard acceleration.

Neither are constant and can never be,in reality.

In the first example
Velocity is changing by THE SAME AMOUNT each second.
Acceleration is THE SAME AMOUNT each second.

In the second example velocity is changing by DIFFERENT AMOUNTS each second
Accelerations is NOT THE SAME each second.

Constant acceleration - variable acceleration.
BUT in both cases velocity is changing

A robber "accelerating" away from cops while they go at the same pace (= speed/velocity).

That must be a NASA robber, performing impossible physics. 

The term "g-force" I believe was first applied to the acceleration felt by the crew of aircraft during fast manoeuvres, such as tight turns and the pull-out from a dive.
The "g-force" value is just how many times normal weight a crew member will feel.

I know what the g-force is supposed to imply. I obviously go against it and have my own name for it as I've shown.
But, we are dealing with what's told to us as g-force and why it works and how.
I could accept answers given with some of it, as in build up for g-force under acceleration but then it becomes nonsensical when g-force apparently stays constant under acceleration. It's crap and makes no sense at all, unless people stick to the spouted gobbledygook method.

It has also been applied to car acceleration and braking.
So saying a car is accelerating at "1-g" is the same as accelerating at 9.8 m/s² and "2-g" is the same as accelerating at 19.6 m/s².

You say "I fail to see how g-force stays constant with acceleration". The "g-force" does not "automatically stay constant".
For a car accelerating, the"g-force" is produced by the force the wheels apply to the road.
The driver controls this with the accelerator and gear selection.

I'm not interested in what the car wheels are doing.
I'm just talking about acceleration or anything, whether it's a boat or a car or a plane or a rocket, etc.

Since force = mass x acceleration,

we know the mass of the car, so we could calculate the needed force and I imagine that drag-car designers do just that.

That's about the best I can do.

Same thing applies. There is no constant acceleration. It cannot work.

consistent is the same as constant, isn't it?

consistent
kənˈsɪst(ə)nt/Submit
adjective
1.
acting or done in the same way over time, especially so as to be fair or accurate.
"the parents are being consistent and firm in their reactions"
2.
(of an argument or set of ideas) not containing any logical contradictions.
"a consistent explanation"

constant
ˈkɒnst(ə)nt/Submit
adjective
1.
occurring continuously over a period of time.
"the constant background noise of the city"
synonyms:   continual, continuous, persistent, sustained, abiding, round-the-clock; More
noun
1.
a situation that does not change.
"the condition of struggle remained a constant"
synonyms:   unchanging factor, unchanging state of affairs, unchanging situation, given
"dread of cancer has been a constant during the last 100 years"

Constant acceleration is far from nonsense. The gravity is at least for a given point on Earth a constant acceleration; 9.81 m/s^2.

Also napoleon's example shows how a constant acceleration of 1 km/h^2 works perfectly fine.

It doesn't work at all. There is no constant in any acceleration. It's impossible.

perhaps if i use an different example.

Not being sarcastic, but is the term compound interest something you are familiar with?
 

Quote from: Gaia_Redonda on March 29, 2017, 04:52:04 AM

Constant acceleration is far from nonsense. The gravity is at least for a given point on Earth a constant acceleration; 9.81 m/s^2.

Also napoleon's example shows how a constant acceleration of 1 km/h^2 works perfectly fine.

It doesn't work at all. There is no constant in any acceleration. It's impossible.

It's pretty stupid to deny something you can test yourself. This is first grade physics.Napoleon's example, spelled out shows how it works.

Now what doesn't work is a robber "accelerating away" from cops while both having the same "pace".

That indeed is physically impossible as acceleration by definition means they don't have the same pace.

Velocity goes from 0 metre per second to 1 meter per second in the first second.
Acceleration is 1 meter per second per second, velocity is 1 meter per second.

In the next second velocity goes to 2 meters per second.
Acceleration is still 1 meter per second per second , so it has stayed the same, but velocity is now 2 meters per second.

Acceleration is given in metres per second squared.
Velocity is metres per second.
They are not the same.

It doesn't matter how you dress it up, you cannot have a constant acceleration. It is impossible.

Same thing applies. There is no constant acceleration. It cannot work.

If a constant force is applied to a mass it accelerates at the constant rate of (^mass/_force) m/s².
End of story.

Quote from: sceptimatic on March 29, 2017, 05:01:58 AM

Quote from: Boots on March 29, 2017, 01:32:27 AM

A linear acceleration of 4m/s² means that every second your velocity is increasing by 4m/s. This is constant acceleration. If you start at a velocity of 0m/s after 4 seconds you are traveling at a velocity of 16m/s.

The acceleration is fine but it is not constant at all.

Quote from: Boots on March 29, 2017, 01:32:27 AM

Non-constant acceleration would be if in the first second your velocity increased by 5m/s but in the second second it increased by 7m/s and in the third it only increased by 3m/s and in the fourth it increased by 1m/s. It has taken you 4 seconds to reach a velocity of 16m/s but it wasn't constant acceleration.

It's no different. Neither are constant.
Your first one can be construed as consistent acceleration and your other can be construed as haphazard acceleration.

Neither are constant and can never be,in reality.

In the first example
Velocity is changing by THE SAME AMOUNT each second.
Acceleration is THE SAME AMOUNT each second.

In the second example velocity is changing by DIFFERENT AMOUNTS each second
Accelerations is NOT THE SAME each second.

Constant acceleration - variable acceleration.
BUT in both cases velocity is changing

If something is changing it is never constant.
Constant acceleration cannot exist whether it's a measured build up or a variation. Neither are constant.

A speed can be constant and so can a velocity, but never acceleration....EVER.

in the first month interest is applied to the principle and added on.

in the second month the the interest is applied to the principle and the interest from last month, and added on.

and so on.

The interest rate is constant. the amount that is being added on each month changes.

If acceleration is constant the velocity keeps going up, like the amount of interest on the credit card ballance if no payment is made.

Quote from: Copper Knickers on March 29, 2017, 01:45:22 AM

Acceleration is rate of change of speed. That is, how quickly or slowly the speed is changing. If the speed changes by the same amount in equal time then the acceleration is said to be constant.
For instance I could accelerate my car at a constant acceleration of 5mph per second. Then after 1 second my speed would be 5mph, after 2 seconds it would be 10mph, and after 10 seconds it would be 50mph.

Although my speed has changed, the rate at which my speed is changing is still 5mph per second. This is what is meant by constant acceleration.

The word you are looking for is, consistent. Constant cannot exist with acceleration no matter how it's dressed up.
It can only exist as fantasy science.

The word constant is just fine:

If a car maintains a speed of 40 mph, we say its speed is constant.

If a car maintains an acceleration of 5 mph per second, we say say its acceleration is constant.

Quote from: CrazyPagan on March 29, 2017, 05:09:49 AM

Quote from: sceptimatic on March 29, 2017, 05:01:58 AM

Quote from: Boots on March 29, 2017, 01:32:27 AM

A linear acceleration of 4m/s² means that every second your velocity is increasing by 4m/s. This is constant acceleration. If you start at a velocity of 0m/s after 4 seconds you are traveling at a velocity of 16m/s.

The acceleration is fine but it is not constant at all.

Quote from: Boots on March 29, 2017, 01:32:27 AM

Non-constant acceleration would be if in the first second your velocity increased by 5m/s but in the second second it increased by 7m/s and in the third it only increased by 3m/s and in the fourth it increased by 1m/s. It has taken you 4 seconds to reach a velocity of 16m/s but it wasn't constant acceleration.

It's no different. Neither are constant.
Your first one can be construed as consistent acceleration and your other can be construed as haphazard acceleration.

Neither are constant and can never be,in reality.

In the first example
Velocity is changing by THE SAME AMOUNT each second.
Acceleration is THE SAME AMOUNT each second.

In the second example velocity is changing by DIFFERENT AMOUNTS each second
Accelerations is NOT THE SAME each second.

Constant acceleration - variable acceleration.
BUT in both cases velocity is changing

If something is changing it is never constant.
Constant acceleration cannot exist whether it's a measured build up or a variation. Neither are constant.

A speed can be constant and so can a velocity, but never acceleration....EVER.

Acceleration is a a RATE of change.
It could be positive, ie getting faster, or negative, getting slower or ZERO .
It can be constant or variable.
acceleration
əksɛləˈreɪʃ(ə)n/Submit
noun
a vehicle's capacity to gain speed.
"the three-litre model has spectacular acceleration"
synonyms:   speeding up, increasing speed, increase in speed, gain in momentum, gathering speed, opening up; technicalrate of change of velocity
"the car's acceleration is sensational"
increase in speed or rate.
plural noun: accelerations
"the acceleration of the industrialization process"
synonyms:   hastening, speeding up, quickening, stepping up, advancement, furthering, furtherance, forwarding, promotion, boosting, boost, stimulation, spur, aid, assistance, facilitation, easing, simplification, expedition, precipitation More
PHYSICS
the rate of change of velocity per unit of time.

Please look at the bold bit
THE RATE OF CHANGE per unit of time.
Not the change per unit of time.

It doesn't matter how you dress it up, you cannot have a constant acceleration. It is impossible.

Why? I agree that you cannot have a constant acceleration forever,
but you can have a constant acceleration for as long as you can apply the constant force.