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FORCES AND PRESSURE

FORCES AND PRESSURE. 4TH ESO Chemistry and Physics IES AMES. FORCES AND PRESSURE. “Pressure makes diamonds” George Patton   “Tears are the safety valve of the heart when too much pressure is laid on it.” Albert Smith. PRESSURE.

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FORCES AND PRESSURE

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  1. FORCES AND PRESSURE 4TH ESO Chemistry and Physics IES AMES

  2. FORCES AND PRESSURE “Pressure makes diamonds” George Patton   “Tears are the safety valve of the heart when too much pressure is laid on it.” Albert Smith

  3. PRESSURE What is the difference between a sharp knife and a blunt knife? You can push a drawing pin into a piece of wood, but you cannot push your finger into the wood even if you exert a larger force. Why? Why do camels have large flat feet? Why do eskimos wear snow-shoes?

  4. PRESSURE Pressure (symbol: 'P') is the force per unit area applied on a surface in a direction perpendicular to that surface.

  5. PRESSURE • Mathematically: P = F/A • P is the pressure, • F is the normal force, • A is the area. • Pressure is a scalar quantity, and has SI units of pascals; 1 Pa = 1 N/m2. • Pressure is transmitted to solid boundaries or across arbitrary sections of fluid normal to these boundaries or sections at every point. • It is a fundamental parameter in thermodynamics and it is related to volume.

  6. PRESSURE UNITS

  7. DENSITY Which is heavier - iron or wood? • In physics, density is mass (m) per unit volume (V) — the ratio of the amount of matter in an object compared to its volume. A small, heavy object, such as a rock or a lump of lead, is denser than a larger object of the same mass, such as a piece of cork or foam. • In the common case of a homogeneous substance, density is expressed as: ρ = m/V • ρ (rho) is the density of the substance, measured in kg·m–3 • m is the mass of the substance, measured in kg • V is the volume of the substance, measured in m3

  8. PRESSURE IN FLUIDS • Since a fluid is a liquid or a gas, its pressure applies in all directions. • Pressure is transmitted throughout the fluid. • Pressure acts in all directions • Pressure increases with depth • Pressure also depends on: • The density of the fluid • The pull of gravity PRESSURE = g x depth x density P= g h d

  9. HYDROSTATIC PRESSURE • The pressure at a given depth in a static liquid is a result the weight of the liquid acting on a unit area at that depth plus any pressure acting on the surface of the liquid. P= g h d

  10. HYDROSTATIC PARADOX If the height of the fluid's surface above the bottom of the five vessels is the same, in which vessel is the pressure of the fluid on the bottom of the vessel the greatest ? The amount of liquid in each vessel is not necessarily the same. The pressure P is the same on the bottom of each vessel.

  11. PASCAL’S PRINCIPLE Any external pressure applied to a fluid is transmitted undiminished throughout the liquid and onto the walls of the containing vessel.

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