Axles fixed to body, wheels spin on axles. This is usually the easier solution, because it doesn’t require any special way of attaching the axles to the body. The axles can simply be taped to the body. However, the axles must be thin enough so that the wheels can spin freely on them. This leads to the problem of the wheels falling off, which can be solved using tape, rubber bands or clay.
Wheels fixed to axles, axles spin on body. While a little harder to make, this solution is generally more reliable. Something that allows an axle to rotate, while keeping it attached to the body, is called a bearing. A simple way to make a bearing is to cut a little piece of straw, and tape it to the underside of the car body. Slide the axle through and attach the wheels to the axle. The straw will keep the axle and wheels on the body, while allowing them to rotate. Many students use the corrugations as a "bearing", slipping the axle through as in the video below.
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