Physical Science 11.3 You will need a calculator today!!
Physical Science 11.3 Speed and Velocity
Speed and Velocity Speed The ratio of the distance an object moves to the amount of time the object moves Units Measured in m/s (meters per second) Average Speed Speed over the entire duration of a trip Instantaneous Speed Speed during a particular instant of time
Average Speed Formula: Average Speed = Distance (d) Time (t) v = d / t
Solving problems!! Ask yourself: What is the problem wanting me to solve for? Find and write the correct formula Substitute what your know into your formula Solve equation (Don t forget units!!)
Average Speed Example #1: You travel 350 meters in 120 seconds. What is your speed? 2.92 m/s
Average Speed Example #2: A train is traveling 10 m/s in 240 seconds. How far did the train travel? 2,400 meters
Example #3: How long did it take an object traveling at 25 m/s to go 2,000 meters? 80 seconds Average Speed
How are instantaneous speed and average speed different? Instantaneous speed: Speed at one particular instant in time Average speed: Speed for the entire duration of a trip
Graphing Speed The slope of a line on a distance-time graph is speed The steeper the slope, the faster you are traveling The flatter the slope, the slower you are traveling
Graphing Motion Example #1 Each line (A and B) represent the motion of two objects. Which object is moving faster? Explain.
Graphing Motion Example #2 Which car has a faster speed: The big car or small car? Explain
Graphing Motion Example #3 Using this graph, what is the average speed of the Big Car and the average speed of the small car?
What is the slope of a distance vs. time graph? Speed!!!
Velocity Velocity: A description of both speed and direction of motion. Velocity is a vector Velocity has the same formula as speed, except we add a direction
Velocity Example #1 An automobile travels 2,500 m north along a straight road for 200 seconds. Calculate the velocity. 12.5 m/s North
Velocity Example #2 A jet liner, moving west, goes from St. Louis towards Kansas City, which is 235 meters away. If it took 1,300 seconds to travel this far, what is the velocity of the aircraft? 0.18 m/s West
Looking at Graphs
Distance vs. Time Graphs Time always runs horizontally (the x-axis). The arrow shows the direction of time. The further to the right, the longer time from the start. Distance runs vertically (the y-axis). The higher up the graph we go, the further we are from the start.
Distance vs. Time Graphs
Distance (m) What is the speed of the airplane? Speed 1600 1400 Denver 1200 1000 800 600 400 200 0 Phoenix 1 2 3 4 5 6 7 Time (s)
Distance (m) Different Slopes Speed = d / t = 2 m/ 2 s = 1 m/s 8 7 6 5 4 3 2 1 0 Speed = d / t = 0 m/2 s = 0 m/s 1 2 3 4 5 6 7 Time (s) Speed = d / t = 4 m/ 2 s = 2 m/s
Distance (m) What is the average speed? Average Below Speed is a distance = Total distance/total vs. time graph time of my = 12 position m/6 s during a race. What = was 2 m/s my AVERAGE speed for the entire race? 14 12 10 8 6 4 2 0 0 1 2 3 4 5 6 6 Time seconds (hr) 12 m
Distance (mi.) Question Below is a distance vs. time graph for 3 runners. Who is the fastest? 7 6 5 4 3 Mr. Leathley Mr. Vaughn Mr. Holbrook 2 1 0 0 1 2 3 4 5 6 35 Time (h) Mr. Holbrook is the fastest. He completed the race in 3 hours
Here is another time-distance graph with 2 journeys represented on the same graph. Each line represents a journey from home to the office. The red line is Dave s journey. The green line is Mike s journey. How long after Dave does Mike leave? 3 seconds After how many seconds does Mike catch up? 7 seconds How far from home are they when they meet? 500 meters D i s t a n c e 1500 m 1000 m 500 m 0 5 10 15 Time (sec)
Question #1 How are speed and velocity different? Velocity is speed with direction 11.3 Assessment Questions Question #2 What shows the speed on a distance-time graph? Slope
11.3 Assessment Questions Question #3 How can two or more velocities be combined? Vector addition
11.3 Assessment Questions Question #4 Which situation represents speed and which one represents a velocity? A boy running at 10 m/s north on a running path Velocity A car moving at 10 m/s while moving along a curved track Velocity A women walking in straight path at 5 m/s Speed
11.3 Assessment Questions Question #5 What is going on in each section of the following distance-time graph?