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Science 20

Science 20. Unit B: Changes in Motion. 1.1a) Average Speed. Average Speed is the total distance traveled divided by the total time taken. Equation: v = d/t Units: m/s or km/h. 1.1b) Scalar and Vector quantities. 2 types of quantities: Scalar = magnitude, no direction.

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Science 20

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  1. Science 20 Unit B: Changes in Motion

  2. 1.1a) Average Speed • Average Speed is the total distance traveled divided by the total time taken. • Equation: v = d/t • Units: m/s or km/h

  3. 1.1b) Scalar and Vector quantities • 2 types of quantities: • Scalar = magnitude, no direction. • Vector = magnitude and direction. • Why is there a difference? • What is the difference between these 2? • Speed. • Velocity

  4. 1.1c) Instantaneous Velocity and Speed • Average velocity/speed gives the average at all times of motion; instantaneous gives it for a specific time/point. • We use instantaneous velocity/speed when asked to calculate the speed/velocity. • Used to study: • Kinematics = how objects move. • Uniform and Uniform accelerated motion. • Dynamics = why objects move. The Physics Classroom

  5. 1.1d) Uniform Motion • Motion where velocity is constant. • Use the formula for average velocity. • The displacement changes at the same rate as the time. • Watch the car… is it uniform motion? • Why is it almost impossible for uniform motion to occur? What force is this? which is uniform?

  6. 1.1e) Non-uniform Motion • Motion where speed or direction (or both) change. • Most common in everyday life… why? • When you speed up, is it uniform motion or not? Why?

  7. 1.1f) Converting units • When converting using the metric system, use khdmdcm (king Henry danced merrily down country meadows); each letter is a division of 10. • Conversion factors are used to help you change more than 1 unit at a time; from km/h to m/s. • Try these: • 23 km/h ---- m/s • 36 m/s ------ km/h

  8. 1.1 Assignment • Please complete the following: • Page 169 #1 and 3. • Page 171 #5. • Review page.

  9. 1.2a) Identifying and Solving problems • Rearranging an equation to find the “unknown”. • 2 basic rules: • When you move a variable to the other side of the equal sign = opposite math operation. • What you do to 1 side, do to the other! • Try these: • V = d/t (solve for t) • KE = ½ mv2 (solve for v)

  10. Practice • If Dana takes her eyes off the road for 2.0s to get a CD, how far did she travel if she is going: • 30 km/h • 50 km/h • 80 km/h • 110 km/h

  11. 1.2b) Driving at night • At night, 60m can be lit up using the headlights of a car. • Flip to page 175 and try #1.4.

  12. Assignment • Please try the following: • Page 177 #1 and 4. • On a sheet of paper, write 2 things that you learned about physics today! Put in your duo tang for the do nows!

  13. Do Now: write the answer in your duo tang. Describe the motion of each car… what type is it?

  14. Topic 1.3a) Average Velocity • Is a vector; has a direction and a value. • Uses displacement NOT distance; what is the difference? • Distance has no direction. • Displacement does! • Example: Navigating with a map.

  15. Speed vs. Velocity • Scalar = speed, distance, time. • Vector = velocity, displacement, time. • Both use similar equations BUT velocity uses displacement divided by time. v =d/t • v = velocity (m/s) • d = displacement (m) • t = time (s)

  16. Problems • Turn to page 182 in your text and work through 1.8 with me. • Try 1.9 on the same page.

  17. 1.3b) Vectors • Vectors are represented by arrows; direction of arrow = direction of vector. • Draw vectors from tip to tail! • Direction can be found 2 ways: • Coordinate system (Math- unit circle) • Navigation system (N S E W) • 2 ways to determine value: • Graphical (draw all to scale and measure). • Analytical (draw a sketch and solve using formulas and trig).Most common!

  18. a) Adding vectors • Sketch the vectors; creating a triangle. • The order DOES NOT matter! • Find the angle and resulting velocity (include direction in answer). • State the angle starting from the tail of the resultant vector. Resultant = the vector I get by adding them together!

  19. b) Examples • A car drives 10km [E] and then 7 km [N]. Determine its displacement.

  20. c) Vector Components • To solve, find the x and y component of the vector. • Use Trigonometry to do this. • Sin, Cos, Tan. • This is what we did with projectile motion! • Pythagoras can be used to determine the resultant velocity! • Label angle as degrees ___ of ___.

  21. 1.4 Graphing motion • Uniform motion = constant velocity. • Uniform accelerated motion = constant acceleration. • Used to tell the “story” of the motion. • 2 graphs: • 1. Position vs. time (d vs. t) • 2. Velocity vs. time (v vs. t) • What should they look like? Why? Lesson 8: Graphs

  22. What does the slope represent (for both)? • What does the area under the v-t graph represent? graphing review

  23. Assignment • Please complete the following: • Distance, Displacement, Velocity and Speed worksheet. • Vector Components worksheet • Page 193 # 3 and 4.

  24. 1.5 Accelerated Motion • Acceleration = change in velocity over a specific time interval. • When something speeds up or slows down. • Formula: a = v /t Units: m/s2

  25. 1.5b) Graphing Accelerated motion • Velocity changes, this changes the shape of the graph you are looking for. • Displacement is found by the area under the v vs. t graph. • Acceleration can be positive (speeding up) and negative (slowing down). • Acceleration is equal to the slope of the line in a v vs.t graph.

  26. Assignment • Please complete the following: • Graphing questions worksheet. • transformers graphing assignment. • Kinematics: acceleration.

  27. 1.6 Displacement during acceleration • When an object is accelerating, the displacement can be found using: The BIG 4 Equations! Use this one!

  28. 1.6b) Free falling objects • Do you accelerate when you fall? Why? • You can find the displacement, time, velocity and acceleration using the 4 equations on the last slide. • The acceleration due to gravity is: a = 9.81 m/s2

  29. Free falling objects • Hypothesized by 2 Greeks: • Aristotle = uniform motion. • Galileo = uniform accelerated motion. • Why are there different explanations? • Galileo was right! The acceleration due to gravity is 9.81m/s2 towards the centre of the earth. Air resistance is negated. • Solve these problems using the big 4 equations.

  30. Initial velocity is always 0m/s in free fall questions; if it is thrown down, that changes! Acceleration is always due to gravity!

  31. Assignment • Please complete the following: • Big 4 questions: Uniform accelerated motion • Free fall pre-lab; lab write-up.

  32. 1.7a) Stopping distance • Reaction distance = distance car travels as driver reacts. • Braking distance = distance car travels from moment brakes are engaged to full stop. • Stopping distance = reaction + braking distance. • Depends on the initial velocity of vehicle.

  33. Apply the Brakes

  34. 1.7b) Area of no return • When driving, the area right before the intersection is the area of no return… if it is yellow, you have to go. • How long should a yellow light last for?. • Turn to page 218 and try #39 to determine this.

  35. 1.8) A closer look at braking • The Force of friction determines how fast a vehicle stops. • It is (a): • contact force between 2 surfaces that opposes acceleration. • Push or pull on an object (a force). • Measured in Newtons (N). friction song! static vs. kinetic friction

  36. 1.8b) Net force • Adding all of the forces that are on an object together is the net force. • When a car is stopping there are 3 forces: • Force of friction between tires and road. • Force of air resistance. • Force applied to the brakes. Friction

  37. 1.8c) Mass • Scalar quantity, measured in kilograms (kg). • The quantity of matter in an object. • The more mass, the larger the force needed to stop the object. • Which would stop first: a mini cooper or a semi-truck? Why? Your Weight On Other Worlds

  38. Kinematics vs. Dynamics • Kinematics = how things move (big 4 equations). • Dynamics = why things move (Newton’s forces). • A balanced system is where all forces balance, the net force is 0N and there is no acceleration.

  39. 1.8d) Newton’s 2nd Law • An object will accelerate in the direction of the net force. • Equation: F = ma where F = net force (N) m = mass (kg) a = acceleration (m/s2)

  40. 1.8e) Free body diagrams • Diagrams that show all the forces acting on the object (in the proper direction). • Draw these for every question! Incline planes

  41. a) examples • I want to push my tarantula’s 8.7kg cage across the table. I push with 29N of force, and there is a force due to friction of 8N between the table and the cage. Determine how much the cage will accelerate.

  42. Assignment • Please complete the following: • Complete #1 and 4a,c,e,g on page 220. • Read through and highlight the important points in the Forces and Friction readings. • Complete #1-4 on “an introduction to forces”.

  43. 1.9) Newton’s First Law • An object in motion will stay in motion and an object at rest will stay at rest unless acted on by another force. • Applied force = force put on object that opposes friction. • Known as the law of inertia (property of an object to resist changes in state of motion).

  44. Newton’s first law!

  45. Assignment • Please complete the following: • #6-10 on “an introduction to dynamics” • Newton’s 1st and 2nd law problems. • Dynamics #1 – Newton’s Laws • Chapter 1 review questions (evens only).

  46. Changes of Motion- Unit B Topic 2: Collisions

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