Force and Pressure

• Introduction to Force

  • Definition: A push or a pull on an object
  • Origin: Results from interaction between objects
  • Effects of Force
    • Can change state of motion (stationary to moving, or vice versa)
    • Can change speed of an object
    • Can change direction of motion
    • Can change the shape of an object

• Types of Forces

  • Contact Forces (Requires physical touch)
    • Muscular Force: Exerted by the muscles of the body
    • Frictional Force: Opposes relative motion between surfaces in contact
  • Non-Contact Forces (Does not require physical touch)
    • Magnetic Force: Exerted by magnets
    • Electrostatic Force: Exerted by a charged body on another
    • Gravitational Force: Pull of attraction exerted by the Earth and universe

• Concept of Pressure

  • Definition: Force acting on a unit area of a surface
  • Formula: $\text{Pressure} = \frac{\text{Force}}{\text{Area}}$
  • Units: Pascal (Pa) or $\text{N/m}^2$
  • Key Relationship
    • Inverse relation with area (Smaller area = Greater pressure for the same force)
    • Examples: Sharp knives, wide straps of school bags, broad tracks on tractors

• Pressure in Liquids and Gases

  • Liquid Pressure
    • Exerted on the walls of the container
    • Depends on the depth of the liquid (increases with depth)
    • Liquids exert equal pressure at the same depth in all directions
  • Atmospheric Pressure
    • Envelope of air surrounding the earth called atmosphere
    • Pressure exerted by this air is atmospheric pressure
    • Decreases with altitude
    • Balanced inside our bodies by our blood pressure