physics paper 2

• • 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
  4. 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
• Forces required to compress, bend or stretch an object

  More than one; it takes multiple forces (in different directions) to deform an object
• Force applied


  Extension of an elastic object
• Inelastic (plastic) deformation


  • A deformation which results in the object being permanently changed
  • The object doesn't return to its original shape when the force is removed
• Equation relating force, spring constant and extension

  1. Force = Spring Constant x Extension

  2. Force (N), Spring Constant (N/m), Extension (m)
• Energy stored in a stretched spring

  Elastic potential energy
• Extension in spring force equation

  Can be replaced with Compression
• Elastic distortion


  • Temporary change, object reverts to original shape once forces are removed
• Inelastic distortion


  • Permanent change in shape, irreversible
• Calculating work done/stored in stretching a spring

  1. Energy (J) = ½ x Spring constant (N/m) x Extension² (m²)

  2. E = ½kx²
• Linear relationship between force and extension

  When an object is deforming elastically; when it has not yet reached the limit of proportionality
• Nonlinear relationship between force and extension

  When the limit of proportionality has been exceeded, and the object is undergoing plastic deformation
• Fluid


  A liquid or a gas
• Pressure in a fluid

  The forces due to pressure act at right angles (normal to) the surface
• Calculating pressure


  1. Pressure (Pa) = Force (N) / Area (m²)

  2. P = F / A
• Atmospheric pressure and height above Earth's surface

  The number of air molecules decreases the higher you go, meaning the weight of air above a point decreases, so the pressure also decreases
• The pressure in a fluid is determined by the fluid and the atmospheric pressure
• Direction of pressure


  Pressure acts in all directions
• How pressure in fluids increases with depth (Higher)

  As the depth increases, the mass of the liquid above the point also increases, so the force produced by that mass increases. Since the force has increased whilst the area has remained constant, the pressure will increase.
• Why pressure in fluids increases with density (Higher)

  As density increases, there are more particles in a given volume of the liquid, hence the weight of the liquid is increased. This means that the force of liquid above a certain point is larger. Since the force has increased, the pressure must also increase.
• Equation for pressure in liquids at different depths (Higher)

  1. Pressure (Pa) = Column height (m) x density (kg/m³) x gravitational field strength (N/kg)

  2. P = hρg
• Upthrust on objects in a fluid (Higher)

  When an object is submerged in fluid, it experiences a higher pressure below it than on top of it, leading to an upwards force called upthrust
• Magnitude of upthrust (Higher)

  Upthrust is equal to the weight of fluid displaced by the object
• Determining if an object will sink or float (Higher)

  If the upthrust is greater than the weight of the object, it will float. If the weight is the greater force, it will sink.
• An object with a density more than that of water would never float (Higher)
• • Kinetic Theory - the idea that the particles in a gas move around randomly and randomly collide with each other
• • Solids:
  • regular lattice structure
  • high density
  • vibrate around fixed positions
  • strong forces of attraction holds them close together
  • definite shape and volume
• • Liquids:
  • lower density
  • weak forces of attraction so free to move around one another
  • definite compact volume but shape can change (flow to fit container)
• • Gases:
  • lowest density
  • very weak forces of attraction so free to move with random motion
  • no definite volume or shape
• • A closed system won't change the mass during a state change.
• • Density - a measure of the mass in a given volume
  • density = mass/volume
• • Water Displacement Practical (Solid Density):

  1. Measure the solid mass using a balance
  2. Fill displacement can with water until the water just starts to come out of the spout
  3. Hold measuring cylinder under the spout and carefully place solid into displacement can
  4. If object floats, carefully push it down until all of it is submerged - finger not in water
  5. Record the volume of water displaced by the solid in the measuring cylinder
• • If value of density is too high in Water Displacement Practical:
  • mass is too high ---> didn't zero/reset balance
  • volume is too low ---> didn't fill up the water level to the spout of the displacement line
• • Internal Energy - the total energy stored by the particles making up a substance or system