Mechanics and materials

• What do scalars describe?

  Only a magnitude
• What do vectors describe?

  Magnitude and direction
• What are examples of scalars and vectors?

  Scalars:

  • Distance
  • Speed
  • Mass
  • Temperature

  
  

  Vectors:

  • Displacement
  • Velocity
  • Force/Weight
  • Acceleration
• When should you use calculation to add vectors?

  When the two vectors are perpendicular
• How do you find the resultant force of two perpendicular forces of 5 N and 12 N?

  Use Pythagoras' theorem

  
• What is the resultant vector (R) when two forces of 5 N and 12 N are perpendicular?

  13 N

  
• How do you find the direction of the resultant vector?

  Use trigonometry
• What is the formula for finding the angle θ in a right triangle?

  tan θ = opposite/adjacent
• What is the direction of the resultant force from the horizontal in the example given?

  22.6°
• When should you use a scale drawing to add vectors?

  When vectors are at angles other than 90°
• How do you find the magnitude and direction of a ship's displacement traveling at a bearing of 060°?

  Draw a scale diagram

  
• What is the formula to resolve a vector V into its components x and y?

  x = V cos θ, y = V sin θ
• What does it mean to resolve vectors?

  To break them into components
• How do you find the vertical component of a velocity of 10 m/s at an angle of 30°?

  y = 10 sin 30°

  
• How do you find the horizontal component of a velocity of 10 m/s at an angle of 30°?

  x = 10 cos 30°

  
• What are the vertical and horizontal components of a ball fired at 10 m/s at 30°?

  8.7 m/s and 5 m/s

  
• How do you find the vertical and horizontal components of weight on an inclined plane?

  Use sin and cos for angles
• What is the condition for an object to be in equilibrium?

  The sum of all forces must be zero
• How can you show an object is in equilibrium?

  • Add horizontal and vertical components of forces
  • Draw a scale diagram forming a closed triangle

  
• What is the formula for the moment of a force about a point?

  Moment = Force × Perpendicular distance
• What is a couple in physics?

  A pair of equal and opposite forces
• How do you find the moment of a couple?

  Multiply one force by the distance
• What does the principle of moments state?

  Sum of anticlockwise moments equals clockwise moments
• How do you find the value of F using moments?

  Set clockwise moments equal to anticlockwise moments
• What is the center of mass of an object?


  The point where mass acts
• What is speed in physics?

  A scalar quantity describing how fast
• What is displacement?

  Overall distance with direction
• What is velocity?

  Rate of change of displacement
• What is acceleration?

  Rate of change of velocity
• What is instantaneous velocity?

  Velocity at a specific point in time
• How is average velocity calculated?

  Final displacement divided by time
• What is uniform acceleration?

  Constant acceleration of an object
• What do acceleration-time graphs represent?

  Change in acceleration over time

  
• What do velocity-time graphs represent?

  Change in velocity over time

  
• What do displacement-time graphs represent?

  Change in displacement over time

  
• What formulas can be used for uniform acceleration?

  v = u + at, s = ut + 0.5at²
• How do you find the final velocity of a stone dropped from 50 m?

  Use v² = u² + 2as
• How do you find the time of fall for a stone dropped?

  Use s = ut + 0.5at²
• What is projectile motion?

  Motion with independent vertical and horizontal components

  
• How do you find the maximum height of a projectile?

  Use vertical component until v = 0