Relative increase in fuel mass

In summary, as the rocket approaches the speed of light, the force required to accelerate it increases, but the impulse available from the fuel remains finite.
  • #1
schonovic
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if a rocketship in space is approaching the speed of light and its relative mass is increasing then i assume the fuel mass is increasing which would make it more potent the closer the ship gets to the speed of light which would give it infinite force when the ship reaches the speed of light. what happens to prevent this from being true?
 
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  • #2
The simple answer from the external frame of reference you imply:

As the mass of the fuel, and the rocketship itself, approaches an arbitrarily large value, so too does the force (or energy) required to accelerate it.


Wikipedia explains related aspects:

.." As seen from the center of momentum frame, the relativistic mass is also the invariant mass...For other frames, the relativistic mass ... includes a contribution from the "net" kinetic energy of the body (the kinetic energy of the center of mass of the body), and is larger the faster the body moves. Thus, unlike the invariant mass, the relativistic mass depends on the observer's frame of reference. ..."

http://en.wikipedia.org/wiki/Relativistic_mass
 
  • #3
schonovic said:
if a rocketship in space is approaching the speed of light and its relative mass is increasing then i assume the fuel mass is increasing which would make it more potent the closer the ship gets to the speed of light which would give it infinite force when the ship reaches the speed of light. what happens to prevent this from being true?
The relativistic mass of a rocket always decreases, never increases. This is for the same reason that the non-relativistic mass of a non-relativistic rocket always decreases: you are spewing lots of mass off the back end. That effect is always greater than the relativistic mass effect.

Also, the quantity of interest is not the force, but the impulse. You can make an arbitrarily high force by reducing the duration of your burn, but that doesn't change the impulse. If you work out the math, the impulse available from the remaining fuel is always strictly decreasing and always finite.
 
  • #4
If you are in a stationary reference frame and watching the ship accelerate, then the mass of fuel on board the ship increases relativistically as the ship goes faster. If you are on board the ship, the fuel mass stays the same as it always was (not counting the mass that's expelled out the rocket engine), being the same density as if the ship had no velocity.
 

1. What is meant by "relative increase in fuel mass"?

The term "relative increase in fuel mass" refers to the change in the amount of fuel present in a system or vehicle, compared to its original amount. It is often expressed as a percentage or ratio.

2. How is relative increase in fuel mass calculated?

Relative increase in fuel mass is calculated by taking the difference between the final and initial fuel masses, dividing it by the initial fuel mass, and then multiplying by 100 to get a percentage. This formula can also be expressed as (Final mass - Initial mass) / Initial mass x 100.

3. Why is relative increase in fuel mass important?

Relative increase in fuel mass is important because it helps us understand the efficiency and performance of a system or vehicle. It can also provide insights into the impact of certain factors, such as weather or driving conditions, on fuel consumption.

4. What are some factors that can affect relative increase in fuel mass?

There are many factors that can affect relative increase in fuel mass, including the type of fuel used, the efficiency of the engine, driving habits and conditions, vehicle maintenance, and external factors such as temperature and wind resistance.

5. How can we reduce the relative increase in fuel mass?

To reduce the relative increase in fuel mass, we can take steps such as using alternative fuels or more efficient engines, practicing fuel-efficient driving habits (such as avoiding rapid acceleration and maintaining a steady speed), and properly maintaining our vehicles. We can also consider external factors, such as choosing routes with less traffic or using vehicles with better aerodynamics.

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