Speed and Velocity 2017

Let’s calculate… Use the diagram to determine the resulting displacement and the distance traveled by the skier during these three minutes.

Answer: The skier covers a distance of 420 m and has a displacement of 140 m, rightward.

One more… What is the coach's resulting displacement and distance of travel?

The coach covers a distance of 95 yards and has a displacement of 55 yards, left.

Motion is a change in position relative to a frame of reference Speed is the distance traveled in a given amount of time Speed=distance time

Standard Units The standard units for speed is in meters per second (m/s) Km per hour is used also In the English system speed is measured usually as miles per hour (m/h) Standard units for time = (s) seconds SI units for distance = (m) meters

Speed vs. Velocity Speed is scalar Ex: v = 20 mph, 20 m/s Speed is the magnitude of velocity. No direction The symbol for speed is s The formula is s= d/t Speed = distance / time

Average Speed vs. Instantaneous Speed Your instantaneous speed , difficult to measure, it is your moment-to-moment speed (what you see on a radar gun or your speedometer) Your average speed is the calculated measure of your speed, distance over time. (what we use)

Velocity Velocity is a combination of speed and direction. It is a vector Ex: v = 20 mph at 15 south of west The symbol for velocity is v. The formula for velocity = v = x/t velocity = displacement / time You will also see it v = d/t just remember if they are asking for velocity add direction. In a car, we can change the velocity three ways: gas pedal to speed up, brake to slow down or steering wheel to change direction

Interchangeable Sometimes the average speed and average velocity are interchangeable. If driving east at 50 miles per hour we say, “ your speed is 50 miles per hour and your velocity is 50 miles per hour east”.

Speed –Time Graphs

Speed–Time graphs are also called Velocity-Time graphs Speed-Time graphs look much like Distance-Time graphs. READ the labels. Time is still plotted on the x-axis. Speed/Velocity is plotted on the y-axis. A straight horizontal line means that the speed is constant. It is not changing over time.

Speed–Time graphs are also called Velocity-Time graphs A straight horizontal line means that the speed is constant. It is not changing over time. A straight line does not mean that the object is not moving.

Increasing speed or velocity This graph shows increasing speed. The object is accelerating.

Slowing down speed or velocity This graph shows decreasing speed. The moving object is slowing down.

What about comparing two moving objects at the same time? Both the dashed and solid line show increasing speed. Both lines reach the same top speed, but the solid one takes longer. The dashed line shows a greater acceleration.

Summary: A speed-time graph shows us the speed of a moving object changes with time. The steeper the graph, the greater the acceleration. A horizontal line means the object is moving at a constant speed or velocity. A downward sloping line means the object is slowing down. Slowing down

Let’s practice While on vacation, Lisa Carr traveled to Padre Island 440 miles one way. Her trip took 8 hours. What was her average speed in mi/hr? Now convert to km/sec 0.02 km/sec