C H A P T E R 2 Kinematics in One Dimension

Mechanics The study of Physics begins with mechanics.

Mechanics The study of Physics begins with mechanics. Mechanics is the branch of physics that focuses on the motion of objects and the forces that cause the motion to change.

Mechanics The study of Physics begins with mechanics. Mechanics is the branch of physics that focuses on the motion of objects and the forces that cause the motion to change. There are two parts to mechanics: Kinematics and Dynamics.

Mechanics The study of Physics begins with mechanics. Mechanics is the branch of physics that focuses on the motion of objects and the forces that cause the motion to change. There are two parts to mechanics: Kinematics and Dynamics. Kinematics deals with the concepts that are needed to describe motion, without any reference to forces. Chapter 2: Kinematics in one dimension Chapter 3: Kinematics in two dimensions

Mechanics The study of Physics begins with mechanics. Mechanics is the branch of physics that focuses on the motion of objects and the forces that cause the motion to change. There are two parts to mechanics: Kinematics and Dynamics. Kinematics deals with the concepts that are needed to describe motion, without any reference to forces. Chapter 2: Kinematics in one dimension Chapter 3: Kinematics in two dimensions Dynamics deals with the effect that forces have on motion. Chapter 4: Dynamics

Distance and Displacement

Starting from origin, O a person walks 90-m east, then turns around and walks 40-m west.

Distance and Displacement Starting from origin, O a person walks 90-m east, then turns around and walks 40-m west. Q: What is the total walked distance?

Distance and Displacement Starting from origin, O a person walks 90-m east, then turns around and walks 40-m west. Q: What is the total walked distance? A: 130-m

Distance and Displacement Starting from origin, O a person walks 90-m east, then turns around and walks 40-m west. Q: What is the total walked distance? A: 130-m Q: What is the displacement?

Distance and Displacement Starting from origin, O a person walks 90-m east, then turns around and walks 40-m west. Q: What is the total walked distance? A: 130-m Q: What is the displacement? A: 50-m, due east.

Displacement The displacement Äx is a vector that points from the initial position to the final position. SI Unit of Displacement: meter (m)

Figure 2-2 One-Dimensional Coordinates

2.2 Speed and Velocity Average Speed Average Velocity Instantaneous Velocity Instantaneous Speed

Average Speed Units for speed: m/s, MPH, kmPH.

Conceptual Checkpoint 2-1 Average Speed

Average Velocity Units for velocity: m/s, MPH, kmPH.

Figure 2-6 Constant Velocity on an x-Versus-t Graph

Example 2-2 Sprint Training

Figure 2-4 Motion Along the X Axis Represented with an x-Versus-t Graph

Figure 2-5a Average Velocity on an x-Versus-t Graph

Figure 2-5b Average Velocity on an x-Versus-t Graph

Instantaneous Velocity and Speed The instantaneous velocity v indicates how fast an object moves and the direction of the motion at each instant of time. The magnitude of the instantaneous velocity is called the instantaneous speed, and it is the number (with units) indicated by the speedometer.

Figure 2-7 Instantaneous Velocity

Figure 2-8 Graphical Interpretation of Average and Instantaneous Velocity

Acceleration

Units: m/s 2, cm/s 2

Table 2-3 Typical Accelerations (m/s 2 ) Ultracentrifuge3 x 10 6 Batted baseball3 x 10 4 Bungee jump30 Acceleration of gravity on Earth9.81 Emergency stop in a car8 Acceleration of gravity on the Moon1.62

Figure 2-9 v-Versus-t Plots for Motion with Constant Acceleration

Example 2-3 An Accelerating Train

Instantaneous acceleration Acceleration at a particular instant is called instantaneous acceleration.

Figure 2-10 Graphical Interpretation of Average and Instantaneous Acceleration

Deceleration

An object speeds up when the acceleration and velocity vectors point in the same direction.

Deceleration An object speeds up when the acceleration and velocity vectors point in the same direction. Whenever the acceleration and velocity vectors have opposite directions, the object slows down and is said to be “decelerating.”

Figure 2-11 Cars Accelerating or Decelerating

Deceleration An object speeds up when the acceleration and velocity vectors point in the same direction. Whenever the acceleration and velocity vectors have opposite directions, the object slows down and is said to be “decelerating.” Example 4: A drag racer crosses the finish line, and the driver deploys a parachute and applies the brakes to slow down. The driver begins slowing down when t 0 = 9.0 s and the car's velocity is v 0 = +28 m/s. When t = 12.0 s, the velocity has been reduced to v = +13 m/s. What is the average acceleration of the dragster?

Kinematics Equations

Figure 2-13a The Average Velocity

Figure 2-14 Velocity Versus Time for the Boat in Example 2-5