lecture2_1 Kinematics

C H A P T E R   2Kinematics 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 dimensionChapter 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 dimensionChapter 3: Kinematics in two dimensions

Dynamics deals with the effect that forces have on motion.Chapter 4: Dynamics

Distance and Displacement

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

position initial ox

position final x

ntdisplaceme oxxx

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

2.2 Speed and Velocity

•Average Speed

•Average Velocity

•Instantaneous Velocity

•Instantaneous Speed

Average Speed

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

Average Velocity

ttt o

o

xxx

v

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

timeElapsed

ntDisplaceme velocityAverage

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.

tt

xv

0lim

The magnitude of the instantaneous velocity is called the instantaneous speed, and it is the number (with units) indicated by the speedometer.

Acceleration

Acceleration

Units: m/s2, cm/s2

Instantaneous acceleration

Acceleration at a particular instant is called instantaneous acceleration.

Deceleration

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.”

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 t0 = 9.0 s and the car's velocity

is v0 = +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