سؤال قراءة ستيب محلول — فهم التفاصيل (تدريب 5305)

(1) In general, smooth surfaces produce less friction than rough surfaces. The strength of the force of friction depends on two factors: how hard the surfaces push together and the types of surfaces involved. Friction also increases if surfaces push hard against each other. If you rub your hands together forcefully, there is more friction than if you rub them together lightly. (2) Even the smoothest objects have irregular, bumpy Surfaces. When the irregularities of one surface come into contact with those of another surface, friction occurs. Friction acts in a direction opposite to the direction of the object's motion. Without friction, a moving object might not stop until it strikes another object. Static Fiction (3) The friction that acts on objects that are not moving is called static friction. Because of static friction, you must use extra force to start the motion of stationary objects. For example, think about what happens when you try to push a heavy desk across a floor. If you push on the desk with a force less than the force of static friction between the desk and the floor, the desk will not move. Rolling Fiction (4) When an object rolls across a surface, rolling friction occurs. This type of friction is important to engineers who design certain products. For example, skates, skateboards, and bicycles need wheels that move freely. So, engineers use ball bearings to reduce the friction between the wheels and the rest of the product. These ball bearings are small, smooth steel balls that reduce friction by rolling between moving parts.