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# Chapter Describing Motion : Velocity & Acceleration - PowerPoint PPT Presentation

Chapter Describing Motion : Velocity & Acceleration. 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.

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Chapter Describing Motion : Velocity & Acceleration

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

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?

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

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?

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.

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

• Average Speed

• Average Velocity

• Instantaneous Velocity

• Instantaneous Speed

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

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

The instantaneous velocityv 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.

Units: m/s2, cm/s2

Acceleration at a particular instant is called instantaneous acceleration.

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

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.”

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?