Section 4 - Mechanics and materials

• State the conditions necessary for a body to be in equilibrium


  For a body to be in equilibrium the sum of all the forces acting on the body must be equal to zero. Also the sum of the moments of the body is zero.
• State fully the conditions that must be satisfied for a system to be in rotational and translational equilibrium


  For translational equilibrium to occur the forces acting on the body must have a sum of zero when the momentum is constant. For rotational equilibrium to occur the sum of the torques (moments) must have a sum of zero.
• What is a vector quantity?

  A vector quantity is a quantity that can be defined by its magnitude and direction.
• Examples of vector quantities

  Acceleration, velocity , weight , friction , displacement
• What is a scalar quantity?

  A scalar quantity is a quantity that can only be defined by it's magnitude.
• Examples of scalar quantities 


  Time , mass, volume , direction, speed , mass, temperature
• There is a velocity-time graph which curves up till it plateaus. It ranges from 0 to 16s. Without calculation (think about the graph), describe how the acceleration of the falling object changes over the first 16s

  The gradient of the velocity time graph shows the acceleration. Since the gradient is decreasing to zero, the acceleration is decreasing.
• What is the area under a velocity-time graph?

  The area under a velocity time graph is displacement
• What is the area under a acceleration-time graph?

  The area under an acceleration-time graph is the velocity.
• What is the are under a force-extension graph?

  The elastic energy potential stored
• Why does the force-extension graph for an inelastic rubber band disprove hookes' law?

  The force-extension graph is not directly proportional. This can be seen on the graph as a straight line is not formed at any point.