A force that resists motion created by objects rubbing together is a. gravity b. friction c. speed d. force
The correct answer and explanation is:
Correct Answer:
b. friction
Explanation (300 words):
Friction is a force that resists the motion of two surfaces sliding or trying to slide across each other. It occurs whenever two objects are in contact and one or both are moving or attempting to move. This force acts in the opposite direction to the motion or the attempted motion.
Friction arises due to the microscopic roughness of surfaces. Even surfaces that appear smooth have tiny irregularities. When two such surfaces come into contact, these irregularities interlock, resisting motion. Additionally, molecular attractions between the surfaces also contribute to friction.
There are several types of friction:
- Static friction: The force that prevents two surfaces from moving past each other. It must be overcome to start motion.
- Kinetic (or sliding) friction: The resistance faced when one object is sliding over another.
- Rolling friction: Occurs when an object rolls over a surface, which is generally less than sliding friction.
- Fluid friction: Resistance from a fluid (liquid or gas), like air resistance.
Friction is both beneficial and detrimental depending on the context. It allows us to walk without slipping, enables cars to grip the road, and lets objects stay in place rather than slide. On the other hand, friction can also cause wear and tear in machines and reduce efficiency by converting useful energy into heat.
Other options in the question are not correct:
- Gravity is the force of attraction between two masses.
- Speed is a measure of how fast something is moving, not a force.
- Force is a general term; friction is a specific type of force.
Thus, the correct answer is friction, as it specifically refers to the resistance to motion when two objects rub against each other.