# WEEK 5

## Pseudo-gravity

OBJECTIVE: Determine the rotational speed of the space settlement and understand how the pseudo-gravity would work inside the space settlement.

CONTENT AREAS: circular motion, Newton's Laws of Motion

In this lesson you will learn how to generate pseudo-gravity in your space settlement:

• What is the source of pseudo-gravity?
• What affects the magnitude of pseudo-gravity?

We recommend you explore the Java program ringworld first.

## How pseudo-gravity works

If you throw a ball straight it will continue traveling straight forward in a line because of inertia (Newton's First Law of Motion). However if you tie the ball to a string and throw it straight while pulling continuously on the string the ball will start moving in a circle. Why? Because your fingers through the string exert force on the ball forcing the ball to change the direction of its velocity. In a rotating orbital space settlement similar to this amusement ride, the floor of the settlement exerts force on you and everything that rests on it. According to inertia (Newton's First Law of Motion) your body, like these riders, would tend to travel in a direction that is tangent to the circular motion. However you will not be able to, because the floor would stop you from going at a tangent and force your body to change the direction of your velocity continuously(the wall in this ride does the same thing). The end result would be you would be pushed firmly in a direction perpendicular to the tangent away from the center of rotation.

We call this force pseudo-gravity, because gravity on earth is caused by the huge mass of earth and it is towards the center of earth. However, on a space settlement the "gravity" is caused by the rotation of the space settlement and it is directed towards outside of the settlement away from the center of rotation. What would happen if the settlement suddenly stops rotating? You and everything else with you would slide along the floor losing momentum to friction until you would become weightless. Since there is no air friction outside the space settlement, energy required to keep it rotating would be minimal.

Would you be aware of the rotation? These amusement park riders certainly are aware of the rotation because they have a reference: the stationary park grounds. However, in an orbital space settlement you would not have a stationary reference point since the whole settlement is rotating with you. So the only thing your body would feel is the force that pushes you firmly on the ground with a force equivalent to earth's gravity. This is the reason even though the earth is rotating on its axis while orbiting the sun and the whole solar system orbiting galactic center we are not aware of these motions because of lack of a reference point (If you are an astronomer you would be aware of these motions because you can use distant stars as your reference point).

In general you can increase the strength of pseudo gravity by:

1. increasing the speed of the rotation (rpm) or
2. increasing the radius of rotation (radius of space settlement).

The rotation rate should not exceed 2 rpm (two rotations per minute) because your body may sense the rotation.

TEACHER LED ACTIVITIES:

ASSIGNMENTS:

• PROJECT LEADER: Makes sure that each member of the group has finished the first four lessons. By this time you should have:
1. an exterior illustration of your space colony
2. the details of life support system
3. the orbiting should have been worked out
• SCIENTIST: Works closely with the artist to make sure the houses, people inside the space settlement are correctly placed according to the direction of pseudo-gravity.
• ARTIST: Draws sketches of the interior of the orbital space settlement.
• RESEARCHER: Does the final calculations using the space settlement calculator.
• TASKMASTER: Adds to the report how the pseudo-gravity will work in the design.
• Take the Quiz for Week 5.

Related Links:

Author: Tugrul Sezen
sezen@nas.nasa.gov

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