RS U2C1A8 Objects and Waves with Changing Speeds

average speed the distance traveled divided by the time taken

average speed average speed = total distance  total time

nonlinear relationship the relationship between two quantities that, when plotted against each other on a graph, do not produce a straight line

nonlinear relationship

Read the top of page 150 Calculating the average speed of an object or wave NOT moving at constant speed

Link to video Before the video, read questions 1 & 2

1. For the 10-second simulation run, how do the average speeds of the three cars compare? Explain your answer. Hint: You don’t need to do any calculations to answer this question. average speed = distance traveled  time The average speeds of the three cars are the same because all three cars travel the same distance in the same amount of time, and average speed = distance traveled  time.

2. Pick one of the three cars and calculate its average speed.

Calculate the average speeds in #’s 3-6. In each case, you only need to know the total distance traveled and the time elapsed to answer the question. p 151 in textbook

Give an answer in miles per hour (mph). 3. Alex’s family travels 200 mi by car to reach their favorite camping spot. Alex’s mother is driving and repeatedly has to change the car’s speed to adjust to the changing flow of traffic. The entire trip takes four hours. What is the average speed of the family’s car? Give an answer in miles per hour (mph).

4. Sofia is driving her car and needs to enter freeway traffic from an on-ramp. In five seconds and over a distance of 100 m, she speeds up from 13.0 m/s to 30.0 m/s. What is her average speed?

5. Richard is scuba diving in the Pacific Ocean 20 m below the surface when he hears the roars of two low-flying military jets passing overhead, 100 m above the surface of the ocean. The speed of sound in air is 332 m/s and in seawater, it is 1535 m/s. The sound waves from the jets take 0.30 s to reach Richard’s ears. What is the average speed of the sound waves?

100 m 20 m The jets are 120 m above Richard (100 m above surface + 20 m below surface).

6. A seismograph detects P waves from an earthquake that originates in the upper mantle 73 km directly below the seismograph. Because the P waves move through different types of rock, their speed is different in each layer depicted in the picture: 8.0 km/s in the upper mantle, 7.0 km/s in the lower crust, and 6.0 km/s in the upper crust. The P waves take 10 s to reach the seismograph. What is the average speed of the P waves?

Distance versus Time & Speed versus Time Graphs Speed (m/s)

Link to Simulation Video 2

7. The distance that the car travels ____________ (increases, decreases, remains the same) as time increases. increases Speed (m/s)

8. The speed of the car ___________ (increases, decreases, remains the same) as time increases. increases Speed (m/s)

Read the bottom of p 152 and all of 153, before you start #9

velocity how fast an object is moving in a given direction speed and direction

velocity East at 750 mph

page 153 in textbook Average Speed when the Direction of Motion Changes

Alex rode his bicycle 9 mi east, then turned around and headed home. What is the average speed of his 2 hour trip?

9. Suppose that starting from home, Alex travels along the road 9 mi east (to the right). Then he turns around and, rather than going back home, he rides to City Hall. His total travel time is 3 h. What is his average speed?

Read p 154

How do we determine a speed for an object or a wave whose speed changes with time? To find the total distance, we add together the distances traveled by the object between changes in direction.

acceleration the change in velocity per unit time

an object has acceleration when: its speed changes (either speeds up or slows down) its direction changes (either turning or moving on a circular path) both its speed and direction change

acceleration a = change in v  time a = (final v - initial v)  time fit (f-i)  t

acceleration

How do we determine a speed for an object or a wave whose speed changes with time? To find the total distance, we add together the distances traveled by the object between changes in direction.