PHYSICS

• Speed


  A scalar quantity that only has a magnitude (size or extent)
• Velocity


  A vector quantity that has both a magnitude and a direction
• Speed vs Velocity


  Speed only has magnitude, velocity has both magnitude and direction
• Distance


  A scalar quantity that only has a magnitude
• Displacement


  A vector quantity that has both a magnitude and a direction
• Calculating speed


  Distance / Time
• Calculating velocity


  Displacement / Time
• People often use the velocity equation regardless of whether they have a direction or not</b>
• The benefit of using velocity is that you can have a negative velocity to represent going backwards
• Objects often don't move at a constant speed but vary along their journey
• Calculating average speed/velocity


  Total distance or displacement / Total time
• Example speeds in m/s


  • Walking: 1.5
  • Running: 3
  • Cycling: 6
  • Car on main road: 25
  • Fast train: 55
  • Plane: >250
• Sound waves travel at 330 m/s in air
• Wind speed can vary from almost 0 m/s to faster than a speeding train, affected by temperature, atmospheric pressure, and structures
• Acceleration


  The rate of change in velocity or how quickly something speeds up or slows down
• Acceleration


  • Measured in meters per second squared
• Delta (Δ)


  Means change
• Delta v (Δv)


  Change in velocity, can also be written as v - u where v is final velocity and u is initial velocity
• Calculating acceleration


  1. Find change in velocity (v - u)

  2. Divide by time
• Acceleration is a vector quantity, so it has direction as well as magnitude and can be negative (implying slowing down or decelerating)
• Acceleration calculated is the average acceleration over the time period, as it may have varied
• Uniform/constant acceleration


  Acceleration is the same rate the entire time
• Second acceleration equation


  • Includes distance instead of time
• If an object starts from stationary, its initial velocity (u) is zero
• Ball dropped from unknown height


  • Final velocity 7 m/s
  • Initial velocity 0 m/s
  • Acceleration due to gravity 9.8 m/s^2
• Calculating height dropped


  1. Use second acceleration equation

  2. Rearrange to solve for distance (s)
• Distance


  The total length of the path traveled, always positive
• Displacement


  The change in position, can be positive or negative depending on direction
• Calculating distance


  Add up the magnitudes of the individual displacements
• Calculating displacement


  Final position minus initial position
• Displacement examples


  • Positive if traveling right/north
  • Negative if traveling left/south
• Relationship between distance and displacement

  Distance is always positive, displacement can be positive or negative
• Example 1: Object moves from -8 to 12 to -20


  • Distance = 20 + 32 = 52 units
  • Displacement = 20 - 32 = -12 units
• Example 2: Sally travels 50m west then 120m south


  • Distance = 50 + 120 = 170m
  • Displacement = √(50^2 + 120^2) = 130m
• 2500 and 120 times 120 is 14400, so if we add these two numbers it gives us 16900
• The square root of 16900 is 130, which is Sally's net displacement
• Megan's journey


  1. Travels 100 meters east

  2. Travels 70 meters north

  3. Travels 140 meters east
• The total distance traveled by Megan is 310 meters
• Finding Megan's net displacement


  1. Travels 100 meters east

  2. Travels 140 meters east

  3. Travels 70 meters north
• Megan's net displacement is 250 meters