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

Chapter 2 Motion in One Dimension

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.

Chapter 2 Section 1 Displacement and Velocity

Point A --------> Point B 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.

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

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?

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

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.

What is the runners Displacement? Distance?

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

Velocity is speed in a given direction

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

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

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.

CLASSWORK PAGE 44 #’S 1-6

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

ANSWER 5.6

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:

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

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)

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

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

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.

Speed Formula: speed = distance time

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

ANSWER Speed avg = distance time Speedavg = 440 mi 8 hrs 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.

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.

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.

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

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

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?

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