SP-401 Skylab, Classroom in Space

[154] Part III - Science Demonstrations
 

Chapter 14: Magnetic Effects.

picture of a section of Skylab in orbit

 

[155] A demonstration of the effects of Earth magnetic field on objects suspended in zero gravity was performed by Scientist Pilot Garriott. It was televised "live" to Earth and was also recorded on videotape. Action sequences and commentary by him were subsequently used in an educational film for use in secondary schools.

The demonstration began with a discussion by the astronaut of the characteristics of the magnetic field surrounding Earth and other dipole magnets. Classroom experiments involving the use of a magnet and north-seeking compass to plot the magnetic lines of force were mentioned. Garriott asked the audience if Earth's magnetic lines of force extend beyond its atmosphere and whether objects in orbit 270 miles above Earth are affected by these lines of force similarly to objects at its surface.

Using small bar magnets, the astronaut showed and explained the tendency of magnets to aline themselves with Earth's magnetic field. A single magnet was released within the zero-gravity environment and began oscillatory movements; however, the magnet ultimately stabilized itself along a line parallel to a magnetic line of force of Earth. Repeated releases of the magnet resulted in identical stabilizations. Also demonstrated during the oscillatory movements was the time required for the magnet to complete one back-and-forth swing as it stabilized. The interval, called the "period of oscillation," appeared constant each time the magnet was released. Garriott explained that this period, together with the magnet's moment of inertia and magnetic dipole moment, is required in the calculation of the strength of Earth's magnetic field.

The tendency for magnets to aline themselves parallel to magnetic lines of force of Earth was further demonstrated by using different combinations of bar magnets. Two magnets, stuck end-to-end, showed the same alinement tendency as the single magnet. However, it was observed that the period of oscillation for the two-magnet combination was approximately twice as long as that for a single magnet. When three magnets were affixed end-to-end and released, they alined themselves in similar fashion, but their period of oscillation was shown to be approximately three times longer.

By affixing magnets side-by-side and releasing them, Garriott compared the stabilization tendency and period of oscillation for one-, two-, and three-magnet combinations. The tendency to become alined along a magnetic line of force was still apparent with three magnets but was more erratic than for the other combinations. Also, because of the erratic behavior, the period of oscillation was more difficult to measure, but it was determined to be approximately twice that observed for the single magnet. The erratic behavior suggests interacting influences of magnetic fields around the three magnets. The observed period of oscillation may be explained as resulting from Skylab's movement to a higher latitude (closer to an Earth pole) during the demonstration, thus being affected by a [156] stronger magnetic force which would cause a shorter period.

As an added demonstration, the astronaut attached a single magnet to a machine nut and released the combination after giving them a spin. The magnet and nut, similar to a gyroscope, exhibited a slow back-and-forth motion and also showed a tendency to stabilize along a magnetic line of force. The back-and-force motion is called the "period of precession" and may be defined as the effect shown by a spinning body when acted upon by an outside, magnetic torque. As the rate of spinning was increased, a lesser period of precession was obvious.

The demonstrations of magnetic effects in space were educationally informative and provided students with an excellent opportunity to observe the effects of Earth's magnetic field on weightless objects. The demonstrations further showed that Earth's magnetic field extends beyond its atmosphere and that the effects of the field on objects in space are comparable to those observed on Earth....

 


The Earth behaves like a large, dipole magnet, with its field extending outward as far as 10 radii.

The Earth behaves like a large, dipole magnet, with its field extending outward as far as 10 radii.



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157]

Scientist Pilot Garriott demonstrated the behavior of bar magnets in the weightless environment of Skylab.

Scientist Pilot Garriott demonstrated the behavior of bar magnets in the weightless environment of Skylab. He released a single one (1), two placed side-by-side (2), and two placed end-to-end (3) at right angles to the magnetic lines of force of Earth's field. In each case, the magnets oscillated slowly before becoming stabilized parallel to the lines of force in Earth's field.


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