• # Why the suitcases with two wheels rattle and move uneven more when we pull it

We all use suit cases with two wheels when we go for tours as they are easy to handle and we need not carry it but we can pull it. It is general observation that suit cases with two wheels rattle and move unevenly towards sides. This is experienced by many. But cases with 4 wheels won't do that. Scientists from France found that if we pull it more fast it may not move this side and that side.Even when pull it fast also some times it will fall down. If we keep the handle nearer to ground chances of falling are very less. But chances are more when it goes through uneven places and up downs.
This is the explanation given by these scientists. Do you agree?
• When the number of wheels decrease, the smoothness in maneuvering also decreases. It becomes harder to concentrate center of gravity above the given wheels. In your suitcase example, the weight is acting downwards when the case is at rest. But later you drag it along you, giving it a momentum. In order to keep the momentum constant, you need to supply the case with a constant speed. Else, the weight falls over one particular wheel, thereby pinning it down, leading to the swirling of the case.
And also because the wheels are very small, the friction applied is great. This contributes to the hardness in handling in rough uneven surfaces.

The stronger a light shines the darker are the shadows around it.

• What I feel that every suitcase is made for a particular weight and not above that. When ever we go for traveling, we have the habit of filling to the brim and even more and close it so tightly and thus the over weight of the suit case has the effect on wheels which are flimsy and made to take on little weight. So when we move them on the ground, all sorts of noise comes from it much to the annoy of others. The wheels should be properly fixed as sometimes due to overweight on one side the alignment would change and even one wheel may break, So we are responsible for overloading the suitcase and that gives inconvenience to us and others.
K Mohan