a. Give an example of the motion of an object in which the frictional force on the object is directed opposite to the motion. b. Give an example of the motion of an object in which the frictional force on the object is in the same direction as the motion.
Solution: Friction most commonly refers to the resisting force generated when two solid surfaces slide against one another. However, there is actually a wide variety of different types of friction that includes skin friction, fluid friction, internal friction, lubricated friction and dry friction. Each of these frictional energies has unique features and dynamics, but the overarching hallmarks of frictional forces remain the same. When two touching surfaces slide against one another, complex interactions occur at an electromagnetic level between the surface's charged particles. These frictional forces convert the kinetic energy generated by their movements into heat. These same principles apply to objects moving through a liquid or through the air, creating different types of frictional energy. A frictional coefficient is computed by determining the ratio of the force of friction between two objects and the force that is pushing them together. Different combinations of surfaces have different frictional coefficients. The shape of an object does not influence fiction; the object's weight and the amount of force applied are the two affecting factors. a)in the case of static friction (friction that exists when the object is not moving), the direction of the friction force is in the opposite direction of the other forces being applied to the object. If this weren't the case, there would be some sort of net force and the object would start accelerating. b) a sphere rolling on a surface. All that matters for direction of friction is the relative motion of the point of contact with the ground, (although in real life the sphere gets distorted and a surface is indeed in contact) the sphere could be moving forward but due to its rotational speed friction might also be forward.