Speed and Velocity

What is Speed? How would you define speed? A measure of the distance an object travels per unit of time What do you think the formula for speed is – knowing the definition?

Units of Speed

Increase Decrease Speeding Up! So, knowing the formula for speed, what would we need to do for distance and what for time to speed up? Increase Decrease

Constant Speed vs. Changing Speed

Constant Speed The rate of change of position in which the same distance is traveled each second

Instantaneous Speed If the speed of an object is changing, it might be helpful to know the object’s speed at a specific moment Instantaneous speed- speed at a specific instant in time

Think! How would the distance the car travels each second change if it were slowing down?

Average Speed The total distance traveled divided by the total time taken to travel that distance

Math You Can Do! d = 360m T = 4s What is your average speed? Average Speed = 360m/4s 90 m/s

Guess What? Average speed is actually velocity! You already know velocity!

Vocabulary So Far Speed Constant Speed Instantaneous Speed Average Speed

Practice!

Remember you have a test September 3rd! Graphing Speed Remember you have a test September 3rd! Be sure to check the website for information as well as the calendar at the bottom of your class’s page!

What is the Formula for Speed One More Time?

So When We Graph Speed… It is a distance-time graph! Graphs that compare the distance an object travels to the time it takes to reach its destination X Axis = Time Y Axis = Distance

Distance Time 5 10 15 20 25 30 35 40 50 60 70

Comparing Speeds When horse A reached the finish line, horse B was only 1.5 km from the starting point of the race Horse A traveled a greater distance than horse B in the same amount of time. Horse A had a greater average speed. Measure the slope of the line to determine speed

They are moving at a constant speed! Work With Your Table What is the instantaneous speed at 40 seconds for horse A and for horse B (You can leave it as a fraction) A = .75/60 = 0.0125 km/s B = .75/60 0.0125 km/s 2) Both horses have show a straight line. What does this show about their speed? They are moving at a constant speed!

Get a Textbook and Your Science Lab Book SILENTLY read “using a distance-time graph to calculate speed” and “distance-time graph and changing speed” on pages 21 & 22 I HIGHLY suggest you take notes as you read Don’t do anything with your lab notebook right now

Let’s Do Some Examples Constant speed Speeding up Slowing down Stopping

Working with the Person NEXT to You Create a distance-time graph example of a constant speed of your own. Calculate the speed of your object by finding the slope of the line. What is the average speed? Create a distance-time graph example for each scenario below. Find the speed for three points along the graph (A, B, C). Then find the average speed of points A, B, and C) Slowing down Stopping Speeding up

Would You Like to Move Your Test to Thursday September 4th ? Velocity Would You Like to Move Your Test to Thursday September 4th ?

Velocity WITH DIRECTION Both the speed and direction of an object Speed: A car travels 60km/h Velocity A car travels 60km/h to the north WITH DIRECTION

Representing Velocity The velocity of an object can be represented by an arrow The length of the arrow indicates speed A greater speed is shown by a longer arrow

Why are the arrows the same length?

Constant Velocity Remember constant speed? Well this is the same thing but with velocity (a direction) Well if there is a direction, and it’s constant, then there has to be a constant direction!

How can velocity change? We can change the speed or the direction

Changing Velocity If either the speed or the direction changes (or both) then the velocity changes A car on a curved track may have a constant speed but, because its direction is changing, its velocity is not constant. We will see in the next section that it is accelerating

Changing Velocity Changing Speed and Direction

So How is Velocity Different From Speed?