Force & Pressure

What this chapter covers

1. Force

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   • Concept of ForceA push or pull changing motion.
   • Unit of ForceNewton (SI) and kilogram-force (kgf).

2. Turning Effect of a Force

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   • ConceptForce turns a body about pivot.
   • Factors Affecting TurningForce magnitude and perpendicular distance.
   • Daily Life ExamplesDoor handles, flour grinders, potter's wheels.
   • Moment of ForceForce times perpendicular distance from pivot.
   • Unit of Moment of ForceSI unit newton-metre; CGS dyne·cm.

3. Thrust

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   • Concept of ThrustForce acting perpendicular on a surface.
   • Effect of ThrustSmaller area gives a greater effect.

4. Pressure

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   • Concept of PressureThrust per unit area (P = F/A).
   • Units of PressurePascal (N/m²), kilopascal and kgf/cm².
   • Dependence of Pressure on AreaSmaller area increases pressure, thrust unchanged.
   • Dependence of Pressure on ThrustLarger thrust increases pressure, area unchanged.
   • Thrust vs PressureTotal normal force versus per area.
   • Daily Life — Decrease in AreaSharp tips push, cut and pierce.
   • Daily Life — Increase in AreaWide tyres, camel feet spread loads.

5. Liquid Pressure

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   • ConceptLiquids press in every direction.
   • Factors Affecting Liquid PressureDepth and density of the liquid.
   • ConsequencesThicker dam bases; hydrostatic paradox.

6. Atmospheric Pressure

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   • ConceptWeight of the air above us.
   • DemonstrationsPressure difference produces a net force.
   • Standard Value76 cm of mercury at sea-level.
   • Daily Life ExamplesStraws, syringes, fountain pens, water pumps.

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