1 / 33

BELLWORK 9/10/18

This chapter discusses motion in one dimension, focusing on displacement, velocity, and scalar quantities. Topics covered include frame of reference, displacement vs. distance, vectors vs. scalars, speed vs. velocity, and how to interpret velocity graphically.

sstuckey
Download Presentation

BELLWORK 9/10/18

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. BELLWORK 9/10/18 • HOW MANY SIG FIGS ARE IN THE FOLLOWING MEASUREMENTS? • A) 0.0025 m • B) 5.00g • C)1250m • D) 105g • E) 3500m

  2. Chapter 2 Motion in One Dimension

  3. Motion in One Dimension • In this chapter, we will only be dealing with motion in one dimension. • Ex: A train moving either forward or backwards along the tracks. It cannot move left and right and up and down. • In further chapters, we will discuss motion in two dimensions. • The branch of physics concerned with motion and forces is called mechanics. • The subset of mechanics that describes motion without regard to its causes is called kinematics.

  4. Chapter 2 Section 1Displacement and Velocity

  5. Frame of Reference • Motion takes place over time and depends on the frame of reference. • In order to measure the distance of an object we must use a frame of reference. Point A --------> Point B - Your frame of reference is a point which remains fixed for the problem in question and has an origin,(starting point) from which the motion is measured.

  6. Displacement is the shortest distance between the starting point and the ending point. OR A change in position Δ x = xf - xi

  7. Turn to Page 41 in your books • What will you select as the frame of reference to measure the gecko’s displacement? • What is the gecko’s displacement in Figure 2?

  8. Displacement vs. Distance • If the gecko in Figure 2 traveled from the 24.5 cm mark to the 85.5 cm mark • Displacement = 61.0 cm and Distance = 61.0cm • BUT • If the gecko traveled from the 24.5 cm to the 85.5 cm, and returned back to the 24.5 cm mark • Displacement = 0 and Distance = 122.0 cm

  9. Round trips • If you return to the starting point (round trips) the displacement will always be = 0. Displacement is: How far away you are from where you started.

  10. What is the runners Displacement? Distance?

  11. Displacement can be + or (-) • See Table 1 on Page 42 • To the right , east, upward, or north = Positive • To the left, west, downward, or south = Negative

  12. Velocity is speed in a given direction

  13. Vavg=Δx (xf– xi) Δt (tf – ti) **ADD formula to your index card

  14. Units • Displacement – SI unit for length is meters • Time – SI Unit for time is seconds • (Velocity) – SI unit is m/s.

  15. Units **Since displacement can be either positive or negative, velocity has to have a direction on your answers; indicating the direction in which the object is traveling.

  16. CLASSWORK • PAGE 44 #’S 1-6

  17. BELLWORK 9/11/18 • Round your answers using the rules for sig figs. • (23.523 + 44.17) / 12 =

  18. ANSWER • 5.6

  19. Vectors vs. Scalars • The mathematical quantities that are used to describe the motion of objects can be divided into two categories. • The quantity is either a vector or a scalar. • These two categories can be distinguished from one another by their distinct definitions:

  20. Vectors vs. Scalars • Scalars are quantities that are fully described by a magnitude (or numerical value) alone. • Vectors are quantities that are fully described by both a magnitude and a direction

  21. Vectors vs. Scalars • Velocity is a vector quantity that has a magnitude (numerical value) and a direction. • Speed has no direction (scalar quantity) • Displacement is a vector quantity that has a magnitude and a direction. • Distance is a scalar quantity (no direction)

  22. Checkpoint • 5m • 30m/s, east • 5 mi, north • 20 degrees celsius • 256 bytes • 4000 calories • Vector or Scalar • Vector or Scalar • Vector or Scalar • Vector or Scalar • Vector or Scalar • Vector or Scalar

  23. Checkpoint Answers • 5m • 30m/s, east • 5 mi, north • 20 degrees celsius • 256 bytes • 4000 calories • Scalar • Vector, has a direction • Vector; has a direction • Scalar • Scalar • Scalar

  24. Speed vs. Velocity • Just as distance and displacement have distinctly different meanings (despite their similarities), so do speed and velocity. • Speed is a scalar quantity that refers to how fast an object is moving. • Speed can be thought of as the rate at which an object covers distance.

  25. Speed • Formula: speed = distance time

  26. CHECKPOINT • While on vacation, Jamie traveled a total distance of 440 miles east. Her trip took 8 hours, what was her average speed?

  27. ANSWER • Speed avg= distance time Speedavg = 440 mi 8 hrs Speedavg = 60 mi/hr This was just her average speed. She may have been traveling 70 mi/hr at some points, or she may have even stopped for food.

  28. Velocity can be determined mathematically or interpreted graphically The velocity of an object can be interpreted graphically if the object’s position is known at specific times along its path. Between 0 and 2 sec. the object moves 10m. Likewise; it moves another 10m between 2 and 4s; etc………. Because the average velocity does not change, the object is moving with a constant velocity of +10m/s. For any position vs. time graph, we can also determine the average velocity by drawing a straight line between any two points on the graph, and finding the slope.

  29. Average Velocity vs. Instantaneous Velocity • Since a moving object often changes its velocity during its motion, it is common to distinguish between the average velocity and the instantaneous velocity. The distinction is as follows. • Instantaneous Velocity - the velocity at any given instant in time. • Average Velocity - the average of all instantaneous velocities; found simply by a displacement / time ratio.

  30. Instantaneous Velocity • Look at the position vs time graph that has a curved slope. • This shows that its velocity increases with time. • Instantaneous velocity is the velocity of an object at some instant or point along its path. • To determine instantaneous velocity, draw a straight line that is tangent to the p-t graph at that instant. • Find the slope of the tangent line

  31. Turn to Page 46 • Look at Figure 7 and copy the graph on a sheet of graph paper. • Show how the instantaneous velocity is 12 m/s t=3.0s

  32. SUMMARY • What is the difference between a vector and a scalar quantity? • What is the difference between distance and displacement? Which one is a vector quantity? • What is the difference between speed and velocity? Which one is a vector quantity? • What is the formula for average speed? average velocity?

  33. Pre-Lab – Physics 400 • Find a Lab group of 4 • Read the lab • Work on Step #2 • Construct your data table

More Related