Chp 4 Speed Velocity and Acceleration Study Guide

Chp. 4: Speed, Velocity, and Acceleration Study Guide

Average Speed � Total distance traveled divided the total time taken to travel that distance. Speed=Distance/Time � Ex: A soccer ball takes 60 seconds to roll 30 meters. Average speed=30 meters/60 sec=0. 5 m/s

Practice Problem � The workers placed 125 meters of asphalt in 2. 5 hours. What was their average speed? � Answer: 50 m/hr � Formula: S=D T � Equation: S = 125 2. 5 � S = 50 m/hr

Formula � If you need to find speed (distance/time) � If you need to find time (distance/speed) � If you need to find distance (speed x time) Formula Fact Triangle

Velocity � The speed and direction of a moving object. � Ex. 200 m/s West (speed and direction) � There are 3 things that can change velocity 1. Change in speed 2. Change in direction 3. Change in both

Changes in Velocity � Ex. A car is on a curving road, so velocity is changing. As long as you’re turning, the velocity is changing. � Ex. A car is moving and then stops at a stop light. Because the car’s speed changed, the velocity changed.

Acceleration �A change in velocity during a period of time. Acceleration=change in speed/time= m/s 2 � When you’re speeding up your velocity and your acceleration move in the same direction � When you’re slowing down, your velocity and your acceleration move in opposite directions.

Acceleration cont. � If time and speed change you have to find the differences of highest data point and lowest data point of the two. � Ex. Times (sec)=1, 2, 3, 4, 5 Difference=5 -1=4 sec Velocity (m/sec, N)=2, 2. 5, 3, 3. 5, 4 Difference=4 -2=2 m/s N Acceleration=2/4=0. 5 m/s 2

Practice Problem � During a bike race, a cyclist accelerates to the north from 8 meters per second to 10 meters per second in 5 seconds to finish the race. What is his acceleration? � Formula: final speed-initial speed Time 10 m/s – 8 m/s = 2 m/s = 0. 4 m/s 2 5 seconds 5 sec

Distance-Time Graphs �A graph comparing distance and time. � X-axis=time, Y-axis=distance

Example of Distance-Time Graph � When speed is constant, distance and time are increasing at the same rate.

Example of Distance-Time Graph � When the graph line is flat (horizontal), the object is not moving. Time is going by, but distance is not increasing.

Example of Distance-Time Graph � When the graph line is curved upward, the object’s speed is increasing because distance is increasing faster than time.

Example of Distance-Time Graph � When the graph line is curved downward towards a flat line, the object’s speed is decreasing because time is increasing faster than distance. Decreasing speed can also look like this

Example of Distance-Time Graph � The steeper the slope of the graph line, the faster the speed. faster slower