Chapter 2: Kinematics in One Dimension Sections 2.1, 2.2, 2.3 S. D Agostino Physics Department Brock University Physics 1P21/1P91 8 September 2016
Outline 1 Overview 2 Definitions 3 Example 1 4 Representing Motion Graphically 5 Example 2
Overview Newtonian mechanics kinematics dynamics Chapter 2: mainly kinematics in one dimension
Position Position is (A) a vector quantity. (B) a scalar quantity. (C) [Neither of the above.]
Displacement Displacement is (A) a vector quantity. (B) a scalar quantity. (C) [Neither of the above.]
Distance Distance is (A) a vector quantity. (B) a scalar quantity. (C) [Neither of the above.]
Velocity Velocity is (A) a vector quantity. (B) a scalar quantity. (C) [Neither of the above.]
Speed Speed is (A) a vector quantity. (B) a scalar quantity. (C) [Neither of the above.]
Displacement For a motion in a straight line, the displacement of the moving object is defined to be (A) the distance travelled. (B) the final position plus the initial position. (C) the final position minus the initial position. (D) [A and B are correct.] (E) [A and C are correct.]
Calculating Displacement An object moves from position x = +3 m to position x = +7 m, then continues to position x = +1 m. The displacement for the first part of the motion is (A) x = 4 m (B) x = +4 m (C) x = 6 m (D) x = +6 m (E) [None of the above.]
Calculating Displacement, Part 2 An object moves from position x = +3 m to position x = +7 m, then continues to position x = +1 m. The displacement for the second part of the motion is (A) x = 4 m (B) x = +4 m (C) x = 6 m (D) x = +6 m (E) [None of the above.]
Calculating Displacement, Part 3 An object moves from position x = +3 m to position x = +7 m, then continues to position x = +1 m. The displacement for the entire motion is (A) x = 4 m (B) x = +4 m (C) x = 6 m (D) x = +6 m (E) [None of the above.]
Calculating Distance An object moves from position x = +3 m to position x = +7 m, then continues to position x = +1 m. The distance travelled for the entire motion is (A) 4 m (B) 6 m (C) 2 m (D) 2 m (E) [None of the above.]
Definition of Average Velocity The average velocity is defined to be (A) distance travelled divided by the time interval. (B) displacement divided by the time interval. (C) time interval divided by the displacement. (D) time interval divided by the distance travelled. (E) [None of the above.]
Calculating Average Velocity An object moves from position x = +3 m to position x = +7 m in 5 s, then continues to position x = +1 m in an additional 3 s. The average velocity for the first part of the motion is (A) 0.8 m/s (B) +0.8 m/s (C) +2 m/s (D) +0.75 m/s (E) [None of the above.]
Calculating Average Velocity, Part 2 An object moves from position x = +3 m to position x = +7 m in 5 s, then continues to position x = +1 m in an additional 3 s. The average velocity for the second part of the motion is (A) 0.8 m/s (B) +0.8 m/s (C) +2 m/s (D) +0.75 m/s (E) [None of the above.]
Calculating Average Velocity, Part 3 An object moves from position x = +3 m to position x = +7 m in 5 s, then continues to position x = +1 m in an additional 3 s. The average velocity for the entire motion is (A) 0.25 m/s (B) +0.25 m/s (C) +1.25 m/s (D) 1.25 m/s (E) [None of the above.]
Definition of Average Speed The average speed is defined to be (A) distance travelled divided by the time interval. (B) displacement divided by the time interval. (C) time interval divided by the displacement. (D) time interval divided by the distance travelled. (E) [None of the above.]
Calculating Average Speed An object moves from position x = +3 m to position x = +7 m in 5 s, then continues to position x = +1 m in an additional 3 s. The average speed for the entire motion is (A) 0.25 m/s (B) 0.25 m/s (C) 1.25 m/s (D) 1.25 m/s (E) [None of the above.]
Motion Diagram (for the motion on the previous slides) x 7 6 5 4 3 2 1 x 7 6 5 4 3 2 1
Position-Time Graph (for motion on previous slides) x 7 6 5 4 3 2 1 1 2 3 4 5 6 7 8 t
Position-Time Graph (for motion on previous slides) x 7 6 5 4 3 2 1 1 2 3 4 5 6 7 8 t
Velocity-Time Graph (for motion on previous slides) v 4 3 2 1 1 2 1 2 3 4 5 6 7 8 t
Position-Time and Velocity-Time Graphs are Related x v t t
Position-Time and Velocity-Time Graphs are Related x v t t
Draw a Velocity-Time Graph Given a Position-Time Graph x v t t
Average Speed and Average Velocity for a Round Trip Example 2: Alice and Basil drive 120 km out of town at an average speed of 60 km/h. Then Basil gets out of the car and bicycles back to town at an average speed of 20 km/h. (a) Determine Basil s average speed. (b) Determine Basil s average velocity.
Example 2: Incorrect Solution (a) average speed = 60 + 20 2 = 40 km/h
Example 2: Correct Solution (a)
Example 2: Correct Solution (b)
Summary definitions of kinematical quantities vectors and scalars basic kinematical calculations graphical representations of motion
Next Time... 2.4 acceleration 2.5 kinematics equations for constant acceleration