31. A large rock does not move even when someone applies a significant force when pushing it. What is the cause of this phenomenon?
Answer: D
The rock does not move due to static friction.
Static friction is the force that prevents the motion of an object when a force is applied. In this case, the large rock remains stationary because the static frictional force acting on it is equal to or greater than the applied force.
A) Nonzero velocity
Nonzero velocity implies that an object is already in motion. Since the question states that the rock does not move, this option is incorrect as it does not apply to the scenario presented.
B) Constant acceleration
Constant acceleration indicates that an object is experiencing a change in velocity over time. However, the rock remains at rest, thus there is no acceleration occurring in this situation, making this option incorrect.
C) Kinetic friction
Kinetic friction acts on an object that is already in motion, opposing its movement. Since the rock does not move, kinetic friction is not relevant to this scenario, rendering this option incorrect.
D) Static friction
Static friction is the correct explanation for why the rock does not move despite the applied force. It is the force that must be overcome for the rock to begin moving and is responsible for maintaining its stationary position.
Conclusion
The correct answer is static friction, as it is the force that counteracts the applied push and keeps the rock in place. All other options either describe scenarios that do not apply to a stationary object or relate to motion, making them inadequate explanations for the phenomenon observed.