topic 15 - forces and matter

• What is meant by the term ‘fluid’?

  A liquid or a gas
• At what angle do the forces due to pressure act on a given surface in a fluid?

  At right angles (normal to) the surface
• What is the equation used to calculate pressure?

  Pressure (Pa) = Force (N) / Area (m²)
• What is the formula for pressure in symbols?

  P = F / A
• Is the statement true or false? The pressure in a fluid is determined by the fluid and the atmospheric pressure.

  True
• Why does atmospheric pressure vary with height above the earth's surface?

  The number of air molecules decreases with height
• How does pressure in fluids increase with depth?

  Mass of liquid above increases with depth
• In what direction does pressure act in a fluid?

  All directions
• What equation shows the magnitude of pressure in liquids at different depths?

  Pressure (Pa) = Column height (m) x density (kg/m³) x gravitational field strength (N/kg)
• Why does pressure in fluids increase with density?

  More particles increase the weight of the liquid
• Why are objects in a fluid subject to an upthrust?

  • Higher pressure below than above
  • Results in an upwards force called upthrust
• What is the magnitude of the upthrust felt by an object?

  Equal to the weight of fluid displaced
• How can you determine if an object will sink or float?

  If upthrust is greater than weight, it floats
• Why would an object with a density more than water never float?

  Not enough volume displaced for upthrust
• How many forces are required to compress, bend, or stretch an object?

  More than one
• What is the relationship between the force applied and the extension of an elastic object?

  Extension is directly proportional to force applied
• What is meant by inelastic (plastic) deformation?

  • Permanent change in shape
  • Object doesn't return to original shape
• What is the equation relating force, spring constant, and extension?

  Force = Spring Constant x Extension
• What are the appropriate units for force, spring constant, and extension?

  Force (N), Spring Constant (N/m), Extension (m)
• What can extension be replaced with in the equation for spring force?

  Compression
• What type of energy is stored in a spring when it is stretched?

  Elastic potential energy
• Differentiate between elastic and inelastic distortion.

  • Elastic distortion: temporary change, reverts shape
  • Inelastic distortion: permanent change, irreversible
• When is there a linear relationship between force and extension?

  When deforming elastically, before limit of proportionality
• When is there a nonlinear relationship between force and extension?

  When limit of proportionality has been exceeded
• How can you calculate the work done/stored in stretching a spring?

  Energy (J) = ½ x Spring constant (N/m) x Extension² (m²)
• What is the formula for work done in stretching a spring in symbols?

  E = ½kx²