# Rapid acceleration and deceleration of Space X's BFR

Given that momentum is the product of speed and weight (Velocity x Weight) would rapid deceleration or acceleration in weighless space, of Space X's BFR have an impact on its passengers. I ask because if it is to travel at 27000km/h most of its journey would be spent accelerating and decelerating very much limited by earthlike g forces as airliners do, therfore minimizing on the reduction of travel time. Would most of the braking and accelerating have to take place in space at zero gravity?

• Please begin by figuring out how long it takes to accelerate to 27000 km/h at 1 G acceleration. 1 G = 9.8 m/s or 35.3 km/h. Each second, you are going 35km/h faster. – Phil Sweet Oct 3 '17 at 21:28

## 1 Answer

The factor here is mass, not weight - weight is the force produced by mass and the effect of gravity.

The same kinds of forces are produced by acceleration. In "weightless space" (zero gravity) a spacecraft accelerating at 1g (9.81 m/s2) will impose the same force on its occupants as earth's gravity.

For a high speed spacecraft, a lot of the time will be spent accelerating and decelerating to keep the force on the occupants within tolerable limits.

• I never considered before that constant acceleration at 1g for half the journey and -1g for the remainder would give a 1g environment for the occupants. Unfortunately this would not be very efficient and regenerative braking would not be an option! – Transistor Oct 3 '17 at 19:37