Speed

1. Define frame of reference and start why it must be designated in order to determine speed. An object or location that is assumed to be stationary. Without stating a frame of reference, it is impossible to determine the speed of an object.

2. Define kinematics. The description of motion without an attempt to explain it.

3. Give a mathematical definition for speed. s = d / t

4. Solve problems concerning average speed. Formative assessment: after a solution strategy is demonstrated by the teacher, students will work the following problems on white boards.

   • Bob goes to the hardware store

   • Bob stops along the way

   • Martha drives at different speeds

   • Martha and Bob play chicken with a buzzy bee between them.

5. State the difference between average and instantaneous as applied to kinematics.

   Average speed: The "t" in the speed equation represents a finite time interval.

   Instantaneaous speed: The "t" in the speed equation represents a length of time that is as short as can possibly be immagined, but not zero. This yeilds speed at an instance, similar to the speed indicated on a speedometer in a car.

Homefun: Read sections 2.1, 2.2, 2.3

Formative Assessment: Physics Investigation

Follow up Questions

Measuring Speeds

6. Describe how the particle model can be used for measuring motion in movies, photographs, and videos. See examples of the high speed strobe photographs of Eugene Edgerton.

   Class Assignment (formative/summative assessment): Answer the section 2,1 questions on page 33, to be turned in at the end of class.

7. Evaluate whether an object is speeding up, slowing down or traveling at constant speed based on the analysis of particle models.

Speeding up: the dots get further apart as time increases.

Slowing down: the dots get closer together as time increases.

Constant Speed: the dots stay the same distance apart

8. Given a particle model, calculate speeds.

9. Given a particle model and the calculated speeds, draw a graph of speed vs. time. Formative assessment: by looking at a dot plot, how can you tell if the object is speeding up?

10. Given a graph of speed vs time, draw a particle model.

     

Homefun (formative/summative assessment):

Pick a video from the high speed strobe photographs of Eugene Edgerton. and write one paragraph summarizing the video and a second paragraph explaining how the video has changed your perception of the event depicted in the video.

Vectors and Scalars

11. Differentiate between vectors and scalars.

    Scalars: quantities that have magnitude (size)

Vectors: quantities that have magnitude and a spacial direction. Vectors are represented by arrows with the length proportional to magnitude.

12. Differentiate between distance and displacement.

    Distance: a scalar quantity that indicates the length of the path an object travels.

Displacement: a vector quantity that indicates change in location or position. The magnitude is always measured along a straight line from the starting to the ending location. The direction points from starting to ending location. Displacement depends only on the starting and ending locations not on the path taken.

Note that the book frequently uses the term position instead of displacement.

13. State the difference between speed and velocity.

    Speed: a scalar quatity = (distance) / (time increment)

Velocity: a vector quantity = (displacement) / (time increment)

14. State the meaning of the sign on a vector. It only indicates direction (forward or backward). It does not indicate if an object is speeding up or slowing down.

15. Calculate average velocities and note how they differ from average speeds.

    Question: if Bob travels a distance of 100 meters around a circular track in 10 seconds, what is his average speed and average velocity?

    Answer: (avg speed) = 10 m/s, (avg velocity) = 0

Homefun (formative/summative assessment): problems 46 to 53, pages 52 to 53

Interpreting Graphs of Displacement vs, Time

16. Determine both average and instantaneous velocities from plots of displacement vs. time graphs. Note: on the displacement vs time graph for an object, the value of the displacement represents the position of the object relative to the starting point (indicated by the origin).

17. Describe the relationship of slope of the displacement vs. time plot and velocity.

    • The slope of the displacement vs. time plot = velocity.

    • The absolute value of slope = the magnitude of velocity.

    • If the absolute value of velocity is increasing the object is speeding up.

    • If the absolute value of velocity is decreasing the object is slowing down.

18. Given a linear plot of displacement vs. time, write an equation for displacement vs. time.

Homefun (formative/summative assessment): problems 54 to 59, page53

Review of Objectives 1- 25 (1-3 days)

Formative Assessments:

1. Work review problems at the board

2. Work practice problems.

Metacognition Problem Solving Question: Can I still work the problems done in class, several hours or days later? Some amount of repetition on the exact same problems is necessary to lock in learning. It is often better to thoroughly understand a single example of a problem type than to work example after example understanding none of them completely.

Relevance: Good test preparation is essential to performance in physics class.

Summative Assessment: Unit exam objectives 1-16