Chapter 2: Motion in One Dimension

Displacement Change in position of an object Frame of reference A point against which position is measured Example: A train traveling between stations It is in motion when measured against the track. It is stationary when measured against a seat.

Displacement Not equal to distance traveled Scalar vs. Vector Distance vs. Displacement

Displacement (x) Straight line distance from the initial position to the final position (change in position) Can be positive or negative

Displacement (x) What is the displacement for the objects shown? Answer: 70 cm Answer: -60 cm

Displacement Sign Conventions Uses a coordinate system Right (or east) ---> + Left (or west) ---> – Up (or north) ----> + Down (or south) ---> –

Speed vs.Velocity Scalar vs. Vector Distance vs. Displacement

Speed Speed does not include direction while velocity does. Speed uses distance rather than displacement. In a round trip, the average velocity is zero but the average speed is not zero.

Average Velocity = (ΔX/Δt) = displacement/time interval Displacement in a given time Average Velocity = (ΔX/Δt) = displacement/time interval

Average Velocity How would you describe the motion shown by this graph?

Average Velocity Describe the motion of each object. Answers Object 1: constant velocity to the right or upward Object 2: constant velocity of zero (at rest) Object 3: constant velocity to the left or downward

Instantaneous Velocity Velocity at a single instant of time Speedometers in cars measure instantaneous speed. Determined by finding the slope at a single point (the slope of the tangent)

0.98 m/s to the east Book Problems Heather and Matt take a 34 minute walk eastward along a straight road to a store 2.0 km away. What is their average velocity in m/s? 0.98 m/s to the east Book Problems

3.47 m/s to the south Book Problems Eugene is 75 km due south of Salem. If Joe rides from Salem to Eugene on his bike in 6.00 hr, what is his average velocity? 3.47 m/s to the south Book Problems

20.83 m/s to the south Book Problems A bus traveled south along a straight path for 3.2 h with an average velocity of 88 km/h, stopped for 20.0 minutes, then traveled south for 2.8 h with an average velocity of 75 km/h. What is the average velocity for the total trip? 20.83 m/s to the south Book Problems

490,000 m to the south Book Problems A bus traveled south along a straight path for 3.2 h with an average velocity of 88 km/h, stopped for 20.0 minutes, then traveled south for 2.8 h with an average velocity of 75 km/h. What is the displacement for the total trip? 490,000 m to the south Book Problems