Introduction to Physics

  1. Units
    1. It/Not It
    2. Unit conversions - make units cancel so you end up with what you want
    3. Conversion to know how to use:
      1. 1 in = 2.54 cm
      2. 1 hr = 3600 s
      3. 1 m = 100 cm (or s or g or etc)
      4. 1 km = 1000 m (or s or g or etc)
      5. 1 m = 1000 mm (or s or g or etc)
      6. 1 kg = 2.2 lbs
      7. 1 mi = 1760 yds
      8. 1 yd = 3 ft
    4. Examples
      1. 25 cm --> ? m
      2. 30 in --> ? km
      3. 5 mph --> ? m/s
      4. 20 km/hr --> ? m/s
      5. 120 lbs = ? kg
  2. Scientific Notation
    1. Used for very small or very large numbers
    2. NO MORE THAN 3 digits, first then decimal than no more than 2 (#.## x 10#)
    3. Examples
      1. 3 x 10-3 = .003
      2. 2.45 x 104 = 24500
      3. .000000076589 = 7.66 x 10-8
      4. 300000000 = 3 x 108
    4. Type into calculator using "Exp" or "ee" button -- find it!
      1. For first number you would type 3 x 10 ee 3 - (or -3 depending on calculator)
      2. 2 . 4 5 x ee 4
      3. 7 . 6 6 ee - 8
      4. 3 ee 8
  3. Graphing
      1. What type of graph is this? (linear)
      2. Where is the title? labels? units?
      3. What is the equation for this graph? (y = mx +b)
      4. Let's substitute --> d = mt + 0
      5. How do you find slope? (y2-y1/x2-x1) -->(60m - 20m)/(12s - 4s) = 40m/8s = 5 m/s
      6. Substitute --> d = (5m/s)t
      7. Known as DIRECT, as d increases, t increases
        1. What type of graph is this? (parabola)
        2. Where is the title? labels? units?
        3. What is the equation for this graph? (y = kx2)
        4. Let's substitute --> d = kt2
        5. How do you find k (constant)? (pick a point) -->

          200 m = (k)(6.4 s)2

          200m = (40.96s2)k

          k =200m/40.96s2 = 4.9 m/s2

        6. Substitute --> d = (4.9 m/s2)t2
        7. Known as DIRECT, as d increases, t increases
          1. What type of graph is this? (hyperbola)
          2. Where is the title? labels? units?
          3. What is the equation for this graph? (y = k/x)
          4. Let's substitute --> F = k/t
          5. How do you find k (constant)? (pick a point) -->

            1 N = k/2s

            k = (1N)(2s) = 2 Ns

          6. Substitute --> F = (2Ns)t
          7. Known as INVERSE, as F increases, t decreases
  4. 5-step method
    1. All word problems MUST be in this format
    2. Helps keep organized
    3. Steps:
      1. Given: Assign know numbers to variables
      2. Find: Assign variable letter to unknowns
      3. Relationship: Choose all needed equations
      4. Solve: Solve for what you want to find (NO NUMBERS!!! USE ALGEBRA)
      5. Compute: Plug in numbers, solve, BOX answer
    4. Always go down.
    5. May use columns
    6. Always use units in first and last step
    7. Example: A room is designed so that it is 50 m wide, 100 m long, and 12 m high. What is the area of the floor? What is the volume of the room?
      1. G: w = 50 m, l = 100m, h = 12m
      2. F: A=? , V=?
      3. R: A = lw, V = lwh
      4. S: A = lw, V = lwh
      5. C: A = (50m)(100m) = 5000 m2, V = (50m)(100m)(12m) = 60000m3
    8. Another example: A round swimming pool needs to be designed so its area is no more than 1200m2, what radius must if have?
      1. G: A = 1200m2
      2. F: r = ?
      3. R: A = (pi)r2
      4. S: r = sqrt(A/pi)
      5. C: r = sqrt (1200m2/3.14) = 19.5m