Physics

• Scalars


  Physical quantities that describe only a magnitude
• Vectors


  Physical quantities that describe magnitude and direction
• Examples of scalars


  • Distance, speed, mass, temperature
• Examples of vectors


  • Displacement, velocity, force/weight, acceleration
• Adding vectors - Calculation

  1. Use Pythagoras to find resultant magnitude

  2. Use trigonometry to find direction
• Adding vectors - Scale drawing

  1. Draw scale diagram using ruler and protractor

  2. Measure magnitude and direction from diagram
• Resolving vectors


  Splitting a vector into perpendicular components using trigonometry

  
• Formulas for resolving vectors: x = V cos θ, y = V sin θ
• Hint for resolving vectors: Use cos for components in the direction of the angle, use sin for components perpendicular to the angle

  
• Resolving vectors - Examples

  • Velocity components of a ball fired at an angle
  • Weight components on an inclined plane
• Equilibrium


  When the sum of all forces acting on an object is zero, so it is either at rest or moving at constant velocity
• Showing equilibrium


  1. Add horizontal and vertical force components to show they equal zero

  2. Draw scale diagram to show forces form a closed triangle
• Moment


  Force multiplied by perpendicular distance from line of action to point
• Couple


  A pair of coplanar forces equal in magnitude but acting in opposite directions
• Principle of moments


  For an object in equilibrium, sum of anticlockwise moments = sum of clockwise moments
• Using principle of moments


  • Finding unknown force from moment equilibrium
• Centre of mass


  Point at which an object's mass acts
• Uniform object


  Centre of mass is at the centre of the object
• Speed


  Scalar quantity describing how quickly an object is travelling
• Displacement


  Vector quantity describing the overall distance and direction travelled from the starting position
• Velocity


  Rate of change of displacement
• Acceleration


  Rate of change of velocity
• Instantaneous velocity


  Velocity at a specific point in time, found from gradient of displacement-time graph
• Average velocity


  Velocity over a specified time frame, found by dividing final displacement by time taken
• Uniform acceleration


  Acceleration is constant
• Acceleration-time graph

  Area under graph is change in velocity
• Velocity-time graph


  Gradient is acceleration, area is displacement
• Displacement-time graph


  Gradient is velocity
• Formulas for uniformly accelerated motion


  • v = u + at
  • s = (u+v)t/2
  • s = ut + at^2/2
  • v^2 = u^2 + 2as
• Applying formulas for uniformly accelerated motion

  • Calculating final velocity and time for a stone dropped from a bridge
• Projectile motion


  Vertical and horizontal components are independent, can be evaluated separately using uniform acceleration formulas
• Projectile motion example


  • Calculating maximum height and time of flight for a ball projected at an angle
• Free fall


  Motion with constant acceleration of g (9.81 m/s^2)
• Friction/Air resistance


  Force opposing motion, converts kinetic energy to other forms
• Lift


  Upward force on objects travelling in a fluid, caused by change in fluid flow direction
• Terminal speed/velocity


  Speed at which frictional/drag forces equal driving forces, so no acceleration
• Air resistance affects both vertical and horizontal components of projectile motion</b>

  
• Newton's 1st law


  An object will remain at rest or travelling at constant velocity until a resultant force acts on it
• Newton's 2nd law


  Acceleration is proportional to the resultant force, F = ma
• Newton's 3rd law


  For every force, there is an equal and opposite reaction force