alleryStart learning →Why is a heavy crate harder to start moving than to keep moving?
AKinetic friction is less than static
BIts mass falls once it is moving
CThe normal force vanishes on moving
DGravity weakens as the crate slides
Answer & Solution
Correct answer: A. Kinetic friction is less than static
1. Before the crate moves, static friction rises to match whatever push is applied.
2. Once the push beats the largest static friction available, the crate suddenly slips.
3. From then on the resisting force is kinetic friction, which is smaller than the static value.
4. So less push is needed to keep the crate going than was needed to start it.
_Source: OpenStax College Physics (CC BY 4.0), Ch 5 "Further Applications of Newton's Laws: Friction, Drag, and Elasticity", section Kinetic Friction_
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