Statics: Forces, Moments, Equilibrium, Stability, and Hydrostatics

All flashcards

What is a force?

A force is a push or pull exerted by one body on another. It is a vector described by its magnitude, direction, and point of application.

How do contact and body forces differ?

A contact force requires direct physical contact, such as a support force. A body force acts through a field without contact, such as gravitational weight.

What is a moment arm?

The moment arm is the perpendicular distance from a reference point or axis to the line of action of a force. The moment magnitude is the force multiplied by this distance.

State Varignon's theorem.

The moment of a force about a point is equal to the sum of the moments of the force's components about that same point.

What are the two conditions for static equilibrium?

The resultant force and the resultant moment must both be zero: $\sum \mathbf{F} = 0$ and $\sum \mathbf{M} = 0$.

Quiz questions

1. Which three characteristics describe the action of a force in statics?Answer: Magnitude, direction, and point of application.
2. What distinguishes a body force from a contact force?Answer: A body force acts through a field without requiring physical contact.
3. How is the magnitude of a force's moment about a point calculated?Answer: Multiply the force magnitude by the perpendicular distance to its line of action: $M = Fd$.
4. A $10\,\text{N}$ force acts with a moment arm of $0.4\,\text{m}$. What is its moment magnitude?Answer: $4\,\text{N}\cdot\text{m}$
5. Why does static equilibrium for an extended body require both force balance and moment balance?Answer: Force balance prevents translational acceleration; moment balance prevents angular acceleration.