Forces and matter P15

• What is meant by the term ‘fluid’?

  A liquid or a gas.
• At what angle do forces due to pressure act on a 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)
• Why does atmospheric pressure vary with height above the earth's surface?

  The number of air molecules decreases with height.
• True or False? The pressure in a fluid is determined by the fluid and the atmospheric pressure.

  True
• In what direction does pressure act in a fluid?

  All directions.
• How does pressure in fluids increase with depth?

  As depth increases, mass of liquid above increases.
• Why does pressure in fluids increase with density?

  More particles in a volume increase weight.
• 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 are objects in a fluid subject to an upthrust?

  Higher pressure below than above the object.
• 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 that of water never float?

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

  More than one
• Why does it take multiple forces to deform an object?

  Because they must act in different directions
• What is the relationship between force applied and extension of an elastic object?

  The extension is directly proportional to the force
• What must not be exceeded for the relationship between force and extension to hold?

  The limit of proportionality
• What is meant by inelastic (plastic) deformation?

  A permanent change in shape
• What are the characteristics of inelastic (plastic) deformation?

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

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

  Force (N), Spring Constant (N/m), Extension (m)
• What type of energy is stored in a spring when it is stretched?

  Elastic potential energy
• What can extension be replaced with in the equation for spring force?

  Compression
• Differentiate between elastic and inelastic distortion.

  • Elastic distortion: temporary change, reverts to original shape
  • Inelastic distortion: permanent change, irreversible
• How can you calculate the work done/stored in stretching a spring?

  Energy = ½ x Spring constant x Extension²
• What is the formula for energy stored in a spring?

  E = ½kx²
• When is there a linear relationship between force and extension?

  When an object is deforming elastically
• What happens when the limit of proportionality is exceeded?

  Nonlinear relationship occurs
• What type of deformation occurs when the limit of proportionality has been exceeded?

  Plastic deformation