You know that the force of friction depends on the nature of the surfaces in contact. Does it also depend on how hard the surfaces press each other? Is the friction acting on an object that is about to move larger than the friction after motion begins? Is the friction which acts on a rolling object less than that on a sliding object? Find answers to these questions and create an infographic. Such observations help explain why the invention of the wheel was a major milestone in human history.
Does the force of friction depend on how hard the surfaces press each other?
Yes, the force of friction depends on how hard the surfaces press each other. The context indicates that an object experiences a downward gravitational force (weight) and an upward normal force from the surface. When surfaces press harder against each other, the normal force increases, which in turn increases the force of friction.
Yes, the friction acting on an object that is about to move is larger than the friction after motion begins. The context notes that an object starts moving only when the applied force is of a larger magnitude than the opposing force of friction. This implies that the initial friction (static friction) that must be overcome is greater than the friction acting once the object is in motion.
Yes, the friction which acts on a rolling object is less than that on a sliding object. The context directly supports this by stating that such observations help explain why the invention of the wheel was a major milestone in human history. Rolling reduces the opposing frictional force compared to sliding.
Explanation
The textbook context introduces the concepts of weight and normal force, which explains why friction depends on how hard surfaces press together. It states that an object moves only when the applied force exceeds friction, implying static friction is greater than sliding friction. Finally, it explicitly links the comparison between rolling and sliding friction to the historical milestone of the wheel's invention, as rolling reduces the force needed to move objects.