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# Average Speed Notes

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### Average Speed Notes

1. 1. Good Morning! <ul><li>Please DO NOW: </li></ul><ul><ul><li>get lab book </li></ul></ul><ul><ul><li>pick up a dry erase board, piece of paper towel, and a skinny dry erase marker for your table (1 of each per table) </li></ul></ul>
2. 2. Good Morning! <ul><li>Today we will: </li></ul><ul><ul><li>conduct an investigation on speed </li></ul></ul><ul><ul><li>take notes </li></ul></ul><ul><ul><li>solve speed problems </li></ul></ul><ul><li>You will need: </li></ul><ul><ul><li>lab book </li></ul></ul><ul><ul><li>textbook </li></ul></ul><ul><ul><li>spiral & binder </li></ul></ul><ul><ul><li>pen and pencil </li></ul></ul>
3. 3. What Do You See?
4. 4. Chapter Challenge <ul><li>As part of your Chapter Challenge, you will need to describe the motion of a motor vehicle while you are driving. Three crucial parts of describing this motion will be: </li></ul><ul><ul><li>following distance </li></ul></ul><ul><ul><li>braking distance </li></ul></ul><ul><ul><li>total stopping distance </li></ul></ul><ul><li>All three of these have a factor in common. What do you think it is? </li></ul>
5. 5. Speed <ul><li>following distance </li></ul><ul><li>braking distance </li></ul><ul><li>total stopping distance </li></ul>the greater the speed, the greater each of these will be
6. 6. Physics Words <ul><li>speed: </li></ul><ul><ul><li>distance traveled in a certain amount of time </li></ul></ul><ul><li>therefore, the unit of speed is always a distance over a time such as </li></ul><ul><ul><li>mi/h – miles per hour </li></ul></ul><ul><ul><li>m/s – meters per second </li></ul></ul><ul><ul><li>km/h – kilometers per hour </li></ul></ul><ul><ul><li>ft/s – feet per second </li></ul></ul><ul><ul><li>cm/min – centimeters per minute </li></ul></ul>
7. 7. Modeling Speed: Strobe Photos <ul><li>There are several ways to describe speed. In our Investigation, you drew models of strobe photos of moving vehicles </li></ul>notice that in the same amount of time, the strobe captures more images of a slower moving car than the faster moving car
8. 8. Modeling Speed: Equations <ul><li>average speed can be found using the equation </li></ul><ul><li>s av = </li></ul><ul><li>where s av = average speed </li></ul><ul><li>Δd = change in distance </li></ul><ul><li>Δt = change in time </li></ul>Δd Δt
9. 9. Modeling Speed: Equations <ul><li>Sample Problem: If you drive a distance of 400 miles in 8 hours, what is your average speed? </li></ul>
10. 10. Average speed <ul><li>An average of 50 mi/h does not tell you your fastest speed or your slowest speed. </li></ul><ul><li>It does tell you that over a certain amount of time, you covered a specific distance </li></ul>
11. 11. Average Speed <ul><li>For instance, you probably weren’t traveling at a speed of 50 mi/h in your neighborhood, and you stopped at traffic lights, and on the freeway, you probably traveled faster than 50 mi/h. </li></ul>
12. 12. Average Speed <ul><li>average speed : total distance traveled in a specific amount of time </li></ul><ul><li>instantaneous speed : the speedometer reading at any given instant </li></ul><ul><li>constant speed: speed that does not change over a period of time </li></ul>
13. 13. Equations <ul><li>All equations can be re-arranged if necessary. For instance, the formula for average speed ( s av = Δd/Δt ) can be arranged to solve for distance or time. </li></ul>
14. 14. Sample Problem <ul><li>You are traveling at 50 ft/s (about 35 mph) and your reaction time is 0.2 s. Calculate the distance you travel during your reaction time. </li></ul>
15. 15. Equation Solving Strategy <ul><li>In physics, when you do calculations it is very important to pay attention to the units you are using. </li></ul><ul><li>Always carry your units through the problem! </li></ul>ALWAYS. REALLY. I’M NOT KIDDING.
16. 16. Sample Problem #3 <ul><li>In an automobile collision, it was determined that a car traveled 150 feet before the brakes were applied. </li></ul><ul><ul><li>If the car was traveling the speed limit of 40 mi/h (60 ft/s), what was the driver’s reaction time? </li></ul></ul>