Speed Average Speed and Instantaneous Speed

What is the formula for finding speed? d = r t, (“dirt”) Distance equals rate times time. d= r= t= distance rate time

d = r x t, (“dirt”) Distance equals rate times time. Speed is: a rate that measures the distance travelled in an amount of time. We can rearrange the “dirt” formula since we will often be calculating speed using distance and time. d = r x t tt r = d ÷ t

Average Speed vs. Instantaneous Speed Average Speed: (r = d ÷ t ) Instantaneous Speed: The difference: average speed = Total distance traveled ÷ total time elapsed Your speed at any exact moment in your trip The average speed takes all the instantaneous speeds and averages them together to find out how fast the object was travelling overall.

During a typical trip to school, your car will undergo a series of changes in its speed. If you were to inspect the speedometer readings at regular intervals, you would notice that it changes often. The speedometer of a car reveals information about the instantaneous speed of your car. It shows your speed at a particular instant in time.

The instantaneous speed of an object is not to be confused with the average speed. Average speed is a measure of the distance traveled in a given period of time; it is sometimes referred to as the distance per time ratio. Suppose that during your trip to school, you traveled a distance of 5 miles and the trip lasted 0.2 hours (12 minutes). Use the speed formula to calculate the average speed of the car:

On the average, your car was moving with a speed of 25 miles per hour. During your trip, there may have been times that you were stopped and other times that your speedometer was reading 50 miles per hour. Yet, on average, you were moving with a speed of 25 miles per hour. Thanks to Physics Classroom

Slope The __________ of a line is the measure of the line’s steepness. We calculate the __________ of a line by finding the ______________ between the coordinates of ________________ and using those numbers to form a _______________. In science, we use the _________ of a distance time graph to tell us ________________. slope difference two points ratio SPEED

We can determine a lot of information from a distance vs. time graph. y/x slope = y/x OR rise/run OR distance/time slope = 1000/10 slope = 100 OR the speed of the car is 100m/s Finding Speed of a Car

You can use the same formula to find distance or time! d = r t r = d ÷ t t = d ÷ r

60 km 5 hours r = d ÷ t r = 60km ÷ 5 hoursr = 12 km/hr

r = d ÷ t 2 stops 1.5 hours r = 60 km ÷ 3.5 hoursr = 17.1 km/hr The steepest part is where she is covering most distance in least time.

r= d / t r= 600 / 3 r= 380 / 0.5 r= 200 mi/hr r= 760 mi/hr

r= d / t r= 800 / 2.5 r= 239 / 0.75 A. 2200= d / 2 B. 2200= d / 3 C. 2200= d / 5 A. d= 4400 mi B. d= 6600 mi C. d= mi Lockheed SR71 plane r= 320 mph r= mph

r= d / t d = r t r= d / t

r= ( km) / ( min) r= 0.1km/min

During which interval did the teacher move the fastest? How can you tell just by looking at the graph? How fast is she moving? During which interval did the teacher move the slowest (and actually move)? How can you tell just by looking at the graph? How fast is she moving? Is there a time when the teacher is not moving? How can you tell just by looking at the graph? What is her speed at this time? From 25 to 30 seconds. It is the steepest line. r = d ÷ t r = 20m/5 sec r = 4 m/s From 120 to 180 seconds. It is the least steep line. r = d ÷ t r = 60m/20 sec r = 3 m/s From 0-20, 30-65, seconds. It is a flat line. 0 m/s.

D D DD DSS SST T T

r= d / t r= 55 / 10 Distance: 10cm  65cm = 55cm Time: 2:00  2:10 = 10 min r= 5.5 cm/min 3 blocks 5 min 15 blocks t = t = 25 min

Physics of the Olympics Banking on Speed: Bobsled

Ticket Out On your sticky note, answer these questions: 1.What is your name? 2.How can we determine the speed of a kid running down the hallway late to class?