topic 15 - forces & matter

• inelastic distortion

  When an object does not return to its original shape when the force is removed. example : a plastic ruler bent beyond its limit
• What is Hooke's law?

  Force is directly proportional to the extension
• formula for hookes law

  force = spring constant x extension

  ( F = kx )
• What does the spring constant measure?

  How stiff the spring is. the larger the spring constant the stiffer the spring
• How does pressure change with fluid depth?

  Pressure increases with fluid depth
• What causes atmospheric pressure?

  The weight of the air above a surface
• What is upthrust and how is it caused?

  The upward force exerted on a submerged object due to the difference in pressure on the top and bottom surfaces
• What determines whether an object floats or sinks in a liquid?

  If the object's weight is less than or greater than the upthrust force
• What is the purpose of a hydraulic system?

  To transmit force using a liquid
• How do you investigate whether a spring or rubber band obeys Hooke's law?

  Procedure:

  1. Attach the spring/rubber band to a rigid support
  2. Apply different weights to the spring/rubber band and measure the extension
  3. Plot a graph of force (weight) vs extension
  4. If the graph is a straight line, the spring/rubber band obeys Hooke's law
  5. If the graph is curved, the spring/rubber band does not obey Hooke's law
• What is the aim of the Hooke's law practical experiment?

  To investigate how the extension of a spring or rubber band changes with applied force and determine if they obey Hooke's law
• What equipment is used in the Hooke's law practical experiment?

  Springs, rubber bands, weights, and a rigid clamp
• elastic distortion

  when an object returns to its original shape when the force is removed. example : a spring stretched within its limit
• formula for work done or energy transferred from an area


  area = 1/2 x force x extension

  ( a =1/2F x X )
• formula for energy transferred if given spring constant and extension

  energy = 1/2spring constant x extension squared

  ( E = 1/2K x X^2 )
• pressure

  pressure is a measure of the force on a unit of surface area where the force is no longer at a right angle to the surface
• formula for pressure

  pressure (Pa) = force normal to surface (N) / area of surface (m^2)
• pressure at sea level

  100,000Pa (one atm - atmospheric pressure )
• atmospheric pressure

  the result of the weight of the air above a surface
• at higher altitudes….

  atmospheric pressure decreases
• formula for pressure in liquid

  pressure = height of column x density of liquid x gravitational strength

  ( p x strange p thing x g )
• displacement

  an object in a fluid displacing some of the fluid
• formula for upthrust

  upthrust = pressure difference x surface area

  ( f = p x a )
• an object floats…

  when its weight is equal to the upthrust
• an object sinks…

  when its weight is greater than the upthrust
• an object that is less dense than the liquid…

  floats
• an object that is more dense than the liquid…

  sinks
• formula for pressure in a hydraulic system

  pressure = force / area

  ( p = f / a )
• formula for extension

  extension = stretched length - original length
• unit for pressure

  pascals ( Pa )