Final answer:
The static friction force before the crate starts moving is greater than the dynamic friction force after it starts moving. This is because the static friction force responds to your push and increases to match your force, while the kinetic friction force is generally less than the static friction force.
The correct answer is: A. Static friction > moving friction.
Step-by-step explanation:
The static frictional force before the crate starts moving is greater than the dynamic frictional force after it starts moving. When you initially push on the crate, the static friction force responds to your push and increases to be equal in magnitude and opposite in direction to your force. However, once the crate starts moving, the frictional force becomes kinetic friction, which is generally less than the static friction force.
For example, if you are trying to slide a heavy crate across a concrete floor, you may push harder and harder on the crate and not move it at all. This is because the static friction force is equal to and opposite your push. But if you push hard enough, the crate will suddenly slip and start moving. Once in motion, it is easier to keep the crate moving because kinetic friction is less than static friction. Adding mass to the crate or lubricating the floor can affect the amount of force required to start and keep the crate moving.
The correct answer is: A. Static friction > moving friction.