Todd Sidon, a pupil at Ardgowan School, asks :-

Does everything float in space?

Marlyn Jakub, a physicist at Otago University, responds.

Once an object or spacecraft leaves the atmosphere of Earth, there is no gas atmosphere to move through and provide the sense of motion from feeling the wind. When all of the forces on the spacecraft are small and the engines are off, the velocity does not change either its magnitude or direction and we could describe the spacecraft as "floating" through space in a straight line. However, several types of forces may affect the spacecraft and force it to follow a curved path.

First, and usually most important,are the effects of gravity acting on each bit of the object. If you were in the spacecraft near the Earth, you would describe your situation as being "weightless" because gravity causes each object in the spacecraft to follow the same curved path. However, the appearance of floating would be deceptive, as another person on the Earth would see the spacecraft as an object orbiting the Earth in a curved path. This gravity-dominated situation is NOT the "floating" through space in a straight line. Even the orbiting spacecraft is always being pulled toward the Earth.

Gravity becomes a dominant force whenever the object is near any large mass such as the Earth, Moon or Sun. Even when the object is far from the Earth, a nearby star such as the Sun could still force the object's path to curve, possibly into an orbital path around the Sun.

The second type of force arises from the particle impact due to light and atomic particles being issued from stars like our Sun. Though this is usually a small force compared to that due to gravity, the "solar wind" is composed of tiny but real particles, and the millions of tiny collisions lightly push the object in space away from the Sun, much like what happens with the tail of a comet.

Finally, if the object in space goes too near large magnetic field sources, then magnetic forces may become involved in changing the direction and speed of the object. Like gravity there is no need for anything to touch the spacecraft in order to apply the magnetic forces. If the object is very small and has an electric charge, then even the Earth's magnetic field can turn or deflect these objects away from the Earth's surface.

So objects in space can seemingly "float", but the object is affected by unseen collisions with particles and by the non-collision forces arising from magnetism and gravity.