GED Science TestPhysical ScienceEasy
A construction worker is attempting to move a heavy crate across a rough concrete floor. They apply a constant horizontal force, but the crate does not move. Which type of friction is preventing the crate from moving?
- AKinetic friction
- BRolling friction
- CStatic friction
- DFluid friction
Show answer & explanationAnswer & explanation
Correct answer: C. Static friction
Static friction is the force that opposes the initiation of motion between two surfaces that are in contact and at rest relative to each other. Since the crate isn't moving, static friction is at play.
Why the other options are wrong
- A. Kinetic friction (or dynamic friction) opposes motion when surfaces are sliding past each other.
- B. Rolling friction opposes motion when an object rolls over a surface.
- D. Fluid friction (or drag) opposes motion through a fluid (liquid or gas).
Static Friction
The force that opposes the initiation of motion between two surfaces in contact that are at rest relative to each other.
- Acts when an object is not yet moving.
- Its magnitude adjusts to match the applied force, up to a maximum.
- Usually greater than kinetic friction.
Memory trick: Friction resists motion: static stops, kinetic slides, rolling rolls, fluid flows.