Question

Using the law of inertia, explain this statement?

During liftoff, astronauts are placed horizontally in the capsule rather than vertically.

Answer 1

We know from Newton's first law, also called Law of Inertia that

An object which is in a state of rest continues to be at rest, and an object in motion continues to be in the state of motion, with the same speed and in the same direction, unless acted upon by an external force.

During liftoff, astronauts experience large force due to acceleration of the rocket. The inertia of the blood often causes it to move out of the head into the legs. This can cause problems with the eyes and brain in particular. Following symptoms may be experienced by astronauts:

• Grey-out, where the vision loses hue.
• Tunnel vision, where peripheral vision is lost in due course of time.
• Blackout, a loss of vision while consciousness is maintained, caused by lack of blood supply to the head.
• G-LOC, a force induced loss of consciousness.
• Death.

Effect of these forces is more pronounced if forces act along the axis aligned with the spine. This produces significant variation in blood pressure along the length of the body.

Experimentally it has been found that the human body is better at surviving these forces when these act perpendicular to the spine.
In general when the acceleration is in the forward direction and the astronaut is lying on his back.

it can be seen from the foregoing that even though law of Inertia is applicable, primarily it is due to survival of human body in supine as compared to vertical position against these forces.