Speed continued Distance – Time Graphs 2.1

A car travels for a half hour at a speed of 40 km/h A car travels for a half hour at a speed of 40 km/h. How far does the car travel? Show all of your work. What are your knowns? What is your unknown? Which formula will you use? Calculate your answers. Include the SI unit in your answer.

Average speed is found by dividing the total distance traveled by the time taken.

Motion with Constant Speed Describing Motion Motion with Constant Speed Suppose you are in a car traveling on a nearly empty freeway. You look at the speedometer and see that the car's speed hardly changes. If you are traveling at a constant speed, you can measure your speed over any distance interval. 2.1

Instantaneous Speed An object in motion can change speeds many times. The speed of an object at one instant of time is the object’s instantaneous speed.

Changing Speed Usually speed is not constant. Describing Motion Changing Speed Usually speed is not constant. Think about riding a bicycle for a distance of 5 km, as shown. 2.1

Sometimes easier to analyze motion on graphs Graphing Motion Sometimes easier to analyze motion on graphs

Graphing Motion Motion can be represented with a distance-time graph. Time is plotted on the x-axis. Distance is plotted on the y-axis. Figure 5 shows the motion of two students who walked across a classroom, plotted on a distance-time graph.

steeper line = greater speed horizontal line = no change in position

Use the graph below to answer the question. From the graph determine which object is moving the fastest. Which object is moving the slowest?

This graph represents 3 runners during a race. Which runner is fastest? What happened to the runner represented by the green line 10 minutes into the race? In 20 minutes, how far did the runner represented by the blue line run?