topic 15

• 15.1 Explain, using springs and other elastic objects, that stretching, bending or compressing an object requires more than one force


  stretching, bending or compressing an object requires more than one force if you just pushed a spring, then it would move in a certain direction. But if you pushed both ends of the spring, the spring would compress
• 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
• 15.2 Describe the difference between elastic and inelastic distortion (elastic distortion)

  Elastic distortion is a temporary change and allows the object to return to its original shape when the forces are removed.
• 15.2 Describe the difference between elastic and inelastic distortion (inelastic distortion)

  inelastic distortion causes permanent change to the objects shape when the forces are removed.it is irreversible
• 15.3 Recall and use the equation for linear elastic distortion including calculating the spring constant:

  force exerted on a spring (newtons,N)= spring constant(newton per metre,N/m)× extension(metres,m)
• 15.4 Use the equation to calculate the work done in stretching a spring:

  energy transferred in stretching (joules,J)= 0.5 × spring constant (newton per metre,N/m)× extension(metre,m)2
• 15.5 Describe the difference between linear and non-linear relationships between force and extension(linear)


  A linear relationship is when an object is deforming elastically-when it has not yet reached the limit of proportionality(goes back to its original shape)
• 15.5 Describe the difference between linear and non-linear relationships between force and extension(non-linear)

  .A non-linear relationship is when the limit of proportionality has been exceeded- the object is undergoing plastic deformation(doesn't go back to its original shape)
• 15.6 Core Practical: Investigate the extension and work done when applying forces to a spring
• 15.7P Explain why atmospheric pressure varies with height above the Earth's surface with reference to a simple model of the Earth's atmosphere


  Atmospheric pressure varies with height above the Earth's surface.
• 15.8P Describe the pressure in a fluid as being due to the fluid and atmospheric pressure


  Pressure in a fluid is due to the depth of the fluid and atmospheric pressure.

  
  

  The deeper you go, the higher the pressure.
• 15.9P Recall that the pressure in fluids causes a force normal to any surface


  The pressure in fluids causes a force normal to any surface.
• 15.10P Explain how pressure is related to force and area, using appropriate examples


  Pressure is a measure of the force on a unit of surface area, where the force is normal to the surface.

  
  

  - Snowshoes reduce the pressure on the snow.
• 15.11P Recall and use the equation:

  pressure (pascal, Pa) = force normal to surface (newton, N) ÷

  area of surface (square metre, m^2)

  
  

  P = F/A

  pressure = force normal to surface ÷ area of surface
• 15.12P Describe how pressure in fluids increases with depth and density

  Pressure in fluids increases with depth; with deeper you are, the more weight above you to exert pressure.

  
  

  It also depends in density. As pressure is due to the depth of the atmosphere above you.

  So water is over 800 times denser than air, so the pressure in water will be greater than in air.
• 15.13P Explain why the pressure in liquids varies with density and depth

  Pressure in liquids varies on the density and depth.

  
  

  The deeper you are, the more water above you so the pressure on the body will increase.

  
  

  The greater the density, the greater volume of the fluid above, we have greater weight, so the pressure will be greater.
• 15.14P Use the equation to calculate the magnitude of the pressure in liquids and calculate the differences in

  pressure at different depths in a liquid:

  
  

  pressure due to a column of liquid (pascal, Pa) = height

  of column (metre, m) × density of liquid (kilogram per

  cubic metre, kg/m^3) × gravitational field strength

  (newton per kilogram, N/kg)

  
  

  P = h× ρ × g

  pressure due to a column of liquid = height

  of column × density of liquid × gravitational field strength
• 15.15P Explain why an object in a fluid is subject to an upwards force (upthrust) and relate this to examples including objects that are fully immersed in a fluid (liquid or gas) or partially immersed in a liquid
• 15.16P Recall that the upthrust is equal to the weight of fluid displaced


  The upthrust is equal to the weight of fluid displaced.
• 15.17P Explain how the factors (upthrust, weight, density of fluid) influence whether an object will float or sink