Physical Science 11 3 Speed and Velocity Speed

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 or km/hr Average Speed over the entire duration of a trip Instantaneous Speed during a particular instant of time

Average Speed Formula: 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 average speed? 2. 92 m/s Example #2: An object travels 100 meters in 4 seconds. What is the objects average speed? 25 m/s

Average Speed Example #3: A train is traveling 10 m/s in 240 seconds. How far did the train travel? 2, 400 meters Example #4: How long did it take an object traveling at 25 m/s to go 2, 000 meters? 80 seconds

How are instantaneous speed and average speed different? • Instantaneous speed is measured at a particular instant in time • Average speed is computed for the entire duration of a trip

Graphing Motion 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

Different Motion Graph Examples

What is the slope of a distance vs. time graph? Speed!!!

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. Example #2 A jet liner passes over St. Louis travelling at 625 m/s, heading straight towards Kansas City, which is 235 meters away. How much time elapses before the aircraft passes over Kansas City if it maintains a constant velocity?

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.

What is the speed of the airplane? Speed = 1, 200 km / 6 hrs = 200 km/hr Denver Phoenix

Different Slopes Speed = d / t = 0 km/2 hr = 0 km/hr Speed = d / t = 4 km/ 2 hr = 2 km/hr Speed = d / t = 2 km/ 2 hr = 1 km/hr

What is the average speed? • Below a distance vs. time graph of my Average Speed is = Total distance/Total = 12 km/6 hr position during race. What was my = 2 a km/hr AVERAGE speed for the entire race? 12 km 6 hours

Question Below is a distance vs. time graph for 3 runners. Who is the fastest? 7 Distance (mi. ) 6 5 Mr. Lebron James 4 Mr. Usain Bolt 3 Mr. Hess 2 1 0 0 1 2 3 4 5 6 35 Time (h) Mr. HESS 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? 1500 m 3 seconds D i 1000 After how many seconds s m does Mike catch up? t 7 seconds a How far from home are they n then meet? c 500 m e 500 meters What is the speed of each person? Dave (Red): 70 m/s Mike (Green): 125 m/s 0 5 10 Time (sec) 15

11. 3 Assessment Questions Question #1 How are speed and velocity different? Velocity is speed with direction Question #2 What shows the speed on a distance-time graph? The slope

11. 3 Assessment Questions Question #3 How can two or more velocities be combined? Vector addition

11. 3 Assessment Questions Question #4 What is going on in each section of the following distance-time graph?