what causes friction?
http://www.school-for-champions.com/science/friction_causes.htm#.VBJa9fldUSM
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Friction is caused by the resistance between two surfaces when they are in contact and moving relative to each other. The roughness and interlocking of microscopic peaks and valleys on the surfaces result in friction. When an object slides, rolls, or moves through a fluid, such as air or water, the frictional force opposes its motion.
To understand the causes of friction, you can consider the following factors:
1. Surface Roughness: The rougher the surfaces of two objects in contact, the higher the frictional force. Rough surfaces have more points of contact, leading to increased resistance.
2. Normal Force: The force exerted by an object perpendicular to the surface it rests on is called the normal force. The greater the normal force between two surfaces, the greater the friction. For example, if you press an object harder onto a surface, such as pressing a book down onto a table, the friction between them will increase.
3. Type of Material: Different materials have different degrees of friction. For instance, surfaces with more texture, like sandpaper, create more friction than smooth surfaces like glass. The nature of the materials in contact affects the amount of friction produced.
4. Lubrication: Adding a lubricant, such as oil or grease, between two surfaces can reduce friction. Lubricants provide a smooth layer that separates surfaces, minimizing direct contact and reducing friction.
5. Temperature: Friction can be influenced by temperature. In some cases, heat generated by friction can increase the interaction between surfaces, enhancing friction. On the other hand, extreme temperatures can make surfaces expand or contract, affecting the degree of friction.
By understanding these factors, you can better comprehend what causes friction and how to manipulate it for various applications.