Topic 15: Forces and Matter

• More than one force has to be applied to compress, stretch and bend a material (distort/deform)
• Elastic - returns to original shape when forces are removed

  Inelastic Distortion - stays in changed shape when forces are removed
• Extension - the increase in length of a spring when its stretched.

  Spring Constant - how many newtons it would take to stretch an object by 1 meter.

  The higher the spring constant, the more stiff the material (proportional)

  Force = spring constant x extension
• Extension in Springs Practical:

  1. Set up apparatus and ensure the 0 of the ruler is level with the bottom of the unstretched spring
  2. Record the extension of the spring as you add 100g masses, starting with no added mass
  3. Add a weight ten times (100g=1N) then repeat experiment with a different spring

  Graph will be proportional (elastic) until the elastic limit where the line will begin to curve (inelastic).

  Area under the graph is the energy transferred to the spring
• Pressure is the force per unit area.

  Perpendicular Force - component of the force which is as right angles to the surface its colliding with

  • perpendicularly at a perfect right angle transfers entire force
  • other angles transfers a smaller force

  Pressure = force x area
• The lower the elevation (height above sea level), the higher the atmospheric pressure:

  • Sea Level - air is more dense so more collisions (greater force) means higher pressure
  • Mountains - lower density
• Density of air decreases with elevation:

  • more weight of air above means greater pressure
  • less weight of air above means lower pressure