Do now for 4/11/13

Take out write up for E74HW: Complete Procedure and Table

for Part B

E74 Measuring Speed

• Today’s target: I will be able to calculate the speed of a moving object.

• Introduce• Gather data for Part A• Write procedure and draw a data table for

Part B• Clean up

E74 Measuring Speed

• What things contribute to car accidents?

• What units do we measure speed in the United States?– Mph = Miles per hour

• Other countries?– Km/h = Kilometers per hour

E74 Measuring Speed

• Other examples of measuring speed:– Rpm = revolutions per minute– m/s = meters per second

• All measurements of speed are measured in units of distance over time– In this activity we will measure speed in the unit

cm/s = centimeters per second

E74 Measuring Speed

• What is the speed of a car that travels 100 miles in 2 hours?– 50 mph

• What is the speed of a car that travels 30 kilometers in a half hour?– 60 km/h

E74 Measuring Speed

• In this activity we will measure the speed of a car that is released from a certain height (Part A)– What is the distance we are measuring? • 100 cm

– What units will we be measuring time in?• Seconds

– What will our units of speed be?• Cm/s = centimeters per second

E74 Measuring Speed

Start timer when rear axle hits here.

Stop timer when rear axle hits 100 cm.

Place a book here so the car doesn’t roll off the table.

E74 Measuring Speed

• Why do you think we need 3 trials?– To improve the quality of your data.

• Gather data for Part A• Part B– Release from the other two heights– How many trials at each height?– How many tables do you need?

Do Now for 4/12/13

• Take out E74• HW: None

E74 Measuring Speed

• Today’s Target: I will be able to review my data from Part A and B and decide whether it is accurate or not.

• Binder clean out and grade evaluation• Go over data• Analysis 1 through 6• Discuss analysis• Key points

Binder Clean Out

• Keep:– General Information– Vocabulary– E Unit Materials

• Complete grade evaluation sheet– Did you earn extra credit???

Sample Data Part ATrial Distance (cm) Time (s) Speed (cm/s)

1 100 1.34 74.6

2 100 1.36 73.5

3 100 1.14 87.7

Average speed = 78.6 cm/s

Sample Data – Part B

E74 Measuring Speed

• 1. According to your data from Part A, what is the speed of the cart?– A typical time for the 100 cm distance is between

1 and 2 seconds. The speed would then be in the range of 50-100 cm/s.

• 2. According to your data from Part B, what is the effect of release height on speed?– Student data will vary but should reflect a trend

of the cart slowing down as release height decreases. For example, the speed went from 123 cm/s to 82cm/s to 56cm/s as the height was decreased from notch A to B to C.

• 3. List some common units for speed. Why are there so many different units?– Three common units for speed are miles per hour

(MPH), kilometers per hour (kph or km/h) and meters per second (m/s). Different speed units are used because there are many different units for distance and time, and some units are more convenient to use than others in different situations.

• 4. What part(s) of your experimental design in Part B:

• a. increased your confidence in the results?– The repeated trials and averaging increased

confidence.• b. decreased your confidence in your results?– Using your eyes to judge where to start the cart and

to determine when to start and stop the timer decreased confidence. You might have also noticed a lag time from seeing to stopping the timer.

• 5. What is a car’s speed, in m/s, if it travels:• a. 5 meters in 0.1 seconds? – 50 m/s

• b. 5 meters in 0.2 seconds? – 25 m/s

• c. 10 meters in 0.2 seconds? – 50 m/s

• 6. Reflection: Why do you think speeding is a factor in about 20% of fatal car accidents?– Answers will vary. Students are likely to suggest

increased stopping distance, less time to swerve out of the way, and greater impact force. Or, they may suggest that a car that is not designed to go faster will be more difficult to control at higher speed.

E74 Measuring Speed – Key Points

• The motion of an object can be described by its position, direction of motion, and speed.

• Average speed is the distance an object travels divided by the time taken to travel that distance.

• Good experimental design requires keeping as many variables as possible the same—except for the one being tested—so that any results can be ascribed to the variable changed.

• Mathematics is important in all aspects of scientific inquiry.

E74 Measuring Speed

• Write up – 5 points– Title, Challenge

• Data table – 5 points• Analysis 1 through 6 – 5 points• Total = 15 points

E76 Speed and Collisions

• Write up – 5 points– Title, Challenge

• Data table – 5 points• Analysis 1 through 3 – 5 points• Total = 15 points

E77 Mass and Collisions

• Write up – 5 points– Title, Challenge

• Data table – 5 points• Analysis 1 through 4 – 5 points• Additional Worksheets – Procedure 5 points• Total = 20 points