# Acceleration Chapter 11 3 Acceleration the rate at

• Slides: 23

Acceleration Chapter 11. 3

Acceleration = the rate at which velocity changes Can be described as a change in speed, change in direction, or a change in both Acceleration is a vector.

Changes in Speed We often use the word acceleration to describe situations where the speed of an object is increasing. Acceleration can be caused by a positive change in speed (increase) or a negative change in speed (decrease).

An INCREASE in speed gives a POSITIVE acceleration. Ex. You car accelerates when the light turns green

A DECREASE in speed gives a NEGATIVE acceleration or DECELERATION. Ex. A car that hits a tree has a very sudden NEGATIVE acceleration https: //www. youtube. com/watch? v=At. IX 4 l. UVQ 0 I

Free Fall Free fall = the movement of an object toward Earth because of gravity SI unit for acceleration is m/s/s or m/s 2

Acceleration of Gravity The acceleration of gravity is 9. 8 m/s 2 Each second an object is in free fall, its velocity increases downward by 9. 8 m/s

MAXIMUM HEIGHT: 128, 097 feet above sea level https: //www. youtube. com/watch? v=FHtv. DA 0 W 34 I FREE FALL: 4 minutes and 20 seconds before pulling his parachute TOP SPEED = 843. 6 mph (Mach 1. 25)

Changes in Direction Think of riding a carousel… Are you accelerating? ? YES! Because you are changing direction, you are accelerating. By Mark Lennihan, AP http: //travel. usatoday. com/destinations/story/2011 -10 -22/Historic-Ohio-carouselfinds-happy-home-in-Brooklyn/50830812/1

Changes in Speed and Direction Roller coaster Your acceleration is constantly changing because of changes in the speed and direction of the roller coaster. Richard Lam/AP http: //www. findingdulcinea. com/features/science/innovations/greatinventions/the-roller-coaster. html

Changes in Speed and Direction Car driving around curve The car is accelerating both because it is changing direction and its speed is decreasing by Linda Wasmer Andrews http: //americanprofile. com/articles/tips-to-manage-motion-sickness/

Constant acceleration = a steady change in velocity The velocity of an object changes by the same amount each second. Ex. Airplane takeoff http: //www. freephotosbank. com/1316. html

Calculating Acceleration •

Example A ball rolls down a ramp, starting from rest. After 2 seconds, its velocity is 6 m/s. What is the acceleration of the ball? List/Visual Question Vi = 0 m/s a = ? Vf = 6 m/s t = 2 s Formula Math Answer w/units 3 m/s 2

Graphs of Accelerated Motion The slope of a speed-time graph is acceleration

4 m/s 2 s http: //labman. phys. utk. edu/phys 135/modules/m 2/1 -d_motion. htm

Linear Graph Linear graph = a graph in which the displayed data forms a straight line.

Nonlinear graph = a graph in which a curve connects the data points. http: //beam-services. ocdsb. ca/~Richard. Taylor/sph 4 u/Methods/acclab. htm

Instantaneous Acceleration = how fast a velocity is changing at a specific instant.

REVIEW 1. A ball just dropped is an example of a) b) c) d) Constant speed Instantaneous speed Combining displacements Free fall

REVIEW 2. Acceleration is equal to a) b) c) d) Distance divided by time Change in speed divided by time The slope of a distance-time graph Change in speed multiplied by time

REVIEW 3. That rate at which velocity is changing at a given instant is described by a) b) c) d) Instantaneous acceleration Average speed Constant speed Vector addition

REVIEW 4. Which graph shows a constant speed? A B