Finish Activity 73Finish Activity 73►Follow procedure steps 3-7Follow procedure steps 3-7►Discuss in your groups and answer Discuss in your groups and answer

analysis questions 3-5analysis questions 3-5

Review Student Sheet 73.1 Review Student Sheet 73.1 ResponsesResponses

Follow-up:Follow-up:►Major ConceptsMajor Concepts

Making decisions often involves trade-Making decisions often involves trade-offs-----giving up one thing to gain offs-----giving up one thing to gain another.another.

The potential for accidents and the The potential for accidents and the existence of hazards impose the need for existence of hazards impose the need for injury prevention and the need to injury prevention and the need to understand the physics of how a car understand the physics of how a car moves (force and motion) moves (force and motion)

Analysis:Analysis:1.1. Compare the features you listed in Compare the features you listed in

Step 2 to the features listed on Step 2 to the features listed on Student Sheet 73.1. How are they:Student Sheet 73.1. How are they:

a.a. similar?similar?► Answers will vary. Share responses.Answers will vary. Share responses.

b.b. different?different?► Answers will vary. Share responses.Answers will vary. Share responses.

2.2. For each feature on Student Sheet For each feature on Student Sheet 73.1 that you drew an “X” next to, 73.1 that you drew an “X” next to, explain why you decided it was less explain why you decided it was less important.important.

• Answers will vary. Share responses.Answers will vary. Share responses.3.3. What factors other than safety do What factors other than safety do

people consider when buying a car?people consider when buying a car?• People typically consider looks (color, People typically consider looks (color,

style), price, cargo size, how many style), price, cargo size, how many passengers it can fit, and fuel passengers it can fit, and fuel economy.economy.

4.4. Do you think car features can:Do you think car features can:a.a. reduce damage, injuries, and fatalities reduce damage, injuries, and fatalities

in car accidents? in car accidents? Explain.Explain.► Possible answer- Features such as seat Possible answer- Features such as seat

belts or airbags reduce the effects of belts or airbags reduce the effects of accidents by padding the impact. A more accidents by padding the impact. A more sturdy frame and/or internal roll bar car sturdy frame and/or internal roll bar car protect the passenger in a rollover.protect the passenger in a rollover.

b.b. prevent accidents? prevent accidents? Explain.Explain.► Possible answer- Brakes that function well Possible answer- Brakes that function well

or mirrors and visors that improve a driver’s or mirrors and visors that improve a driver’s ability to see can prevent accidents. Less ability to see can prevent accidents. Less height can prevent rollovers and better height can prevent rollovers and better handling (or greater acceleration) can help handling (or greater acceleration) can help a driver avoid accidents.a driver avoid accidents.

5.5. Which vehicle do you think is safer- Which vehicle do you think is safer- Vehicle 1 or Vehicle 2? Vehicle 1 or Vehicle 2? ExplainExplain what what data convinces you that this vehicle is data convinces you that this vehicle is safer than the other one.safer than the other one.

• Vehicle 1 has a greater height and mass, Vehicle 1 has a greater height and mass, lower top speed, and slower acceleration. lower top speed, and slower acceleration. This would make it safer, especially for the This would make it safer, especially for the 15-24 year old group since they would not 15-24 year old group since they would not be able to go as fast and would have more be able to go as fast and would have more mass to protect them in a collision.mass to protect them in a collision.

• Based on the number of airbags and shorter Based on the number of airbags and shorter stopping distance, vehicle 2 is safer. It stopping distance, vehicle 2 is safer. It protects more people due to the airbags protects more people due to the airbags and can respond more quickly (stopping and and can respond more quickly (stopping and accelerated) to help avoid accidents.accelerated) to help avoid accidents.

Activity Activity 7474

Title:Title: Measuring Speed Measuring Speed

Background Information:Background Information:►SpeedSpeed

An object in motion takes time to change An object in motion takes time to change its position. Speed is the measurement of its position. Speed is the measurement of the rate of change in position and can be the rate of change in position and can be linear or rotational. The units for speed are linear or rotational. The units for speed are a distance or an angle per unit of time, a distance or an angle per unit of time, such as miles per hour or degrees per such as miles per hour or degrees per second.second.

►VelocityVelocity Speed (s) and velocity (v) are related Speed (s) and velocity (v) are related

concepts but are not the same thing. The concepts but are not the same thing. The velocity of an object includes both its velocity of an object includes both its speed and its direction.speed and its direction.

Speed vs. VelocitySpeed vs. Velocity►What is the difference?What is the difference?

The velocity of an object includes both The velocity of an object includes both its speed and its direction.its speed and its direction.

More vocabularyMore vocabulary►tested variabletested variable: the variable that is : the variable that is

manipulated (changed) in an experimentmanipulated (changed) in an experiment

►controlled variablescontrolled variables: the variables that : the variables that are not changed in an experiment.  also are not changed in an experiment.  also called "controls“ or independent variable.called "controls“ or independent variable.

►responding variableresponding variable: the variable you : the variable you are measuring in an experiment. Also are measuring in an experiment. Also called dependent variable.called dependent variable.

What things can contribute What things can contribute to a car accident?to a car accident?

►Speeding or going too fastSpeeding or going too fast► In the United States, car speed is In the United States, car speed is

typically measured in mph.typically measured in mph.►km/h is used for car speed in other km/h is used for car speed in other

countries. countries. ►Scientists often measure everyday Scientists often measure everyday

speeds in m/s.speeds in m/s.►Today, we will measure speed in cm/s.Today, we will measure speed in cm/s.

Read E-7Read E-7Part APart A

Problem:Problem: How can you measure the How can you measure the speed of a moving cart?speed of a moving cart?

Hypothesis Part A:Hypothesis Part A: If you ______________, If you ______________, then you can ______________________.then you can ______________________.

How do people measure How do people measure speed?speed?

►SpeedometerSpeedometer►Radar GunRadar Gun►Total Distance/Total TimeTotal Distance/Total Time

ProcedureProcedure►Step #8 – Why do you use three trials?Step #8 – Why do you use three trials?►Watch for Watch for ERRORERROR. What is this?. What is this?

Timing errors may cause the time to be too Timing errors may cause the time to be too long or too short.long or too short.

You may stop the watch too soon, and You may stop the watch too soon, and sometimes too late. sometimes too late.

Your reaction time may effect the timing.Your reaction time may effect the timing. Taking the average of 3 trials can limit the Taking the average of 3 trials can limit the

error.error. You may need to do an addition trial if one You may need to do an addition trial if one

is too far off from the others.is too far off from the others.

Minimize ErrorsMinimize Errors►Release the cart the same way each Release the cart the same way each

time.time.►Try to get data the is Try to get data the is ACCURATEACCURATE and and

REPRODUCIBLEREPRODUCIBLE..► If you get 10 m/s, 11 m/s, and 25 m/s, If you get 10 m/s, 11 m/s, and 25 m/s,

you may want to redo the third trial.you may want to redo the third trial.►Put a book to stop the cart. The cart Put a book to stop the cart. The cart

SHOULD NOT roll off the table.SHOULD NOT roll off the table.

Data/Evidence:Data/Evidence:TrialTrial Distance (cm)Distance (cm) Time (s)Time (s) Speed (cm/s)Speed (cm/s)

11 100100

22 100100

33 100100

Always include units

Average

Part A DiscussionPart A Discussion►What is a variable?What is a variable?

A variable is what we change, measure and A variable is what we change, measure and control in an experiment. They are the control in an experiment. They are the factors that influence the speed of the cart.factors that influence the speed of the cart.

►What variable did we test?What variable did we test?There was no tested variable. You did not There was no tested variable. You did not change or manipulate any factors.change or manipulate any factors.

►What variables did we control?What variables did we control?the track (release height, angle & surface)the track (release height, angle & surface)the cart’s massthe cart’s mass

Part BPart BProblem:Problem: What will happen to the speed What will happen to the speed

of the cart if we change the release of the cart if we change the release height of the cart?height of the cart?

Hypothesis:Hypothesis: If you lower the release If you lower the release height of the cart, then height of the cart, then ____________________.____________________.

How will you test your How will you test your hypothesis?hypothesis?

Write a procedure to test your Write a procedure to test your hypothesis.hypothesis.

How many trials?How many trials?

What are your variables other than What are your variables other than height?height?

Data/Evidence:Data/Evidence:

Make 3 tables, one for each Make 3 tables, one for each release height (A, B, and C). release height (A, B, and C). Measure the time over 50 cm. Measure the time over 50 cm. Make sure you title your tables.Make sure you title your tables.

Ex.: Ex.: Release height ARelease height ARelease height BRelease height BRelease height CRelease height C

Calculating SpeedCalculating SpeedWhy did we use the “average value”?Why did we use the “average value”?

What does it mean if your data is What does it mean if your data is accurate?accurate?

What does it mean if your data is What does it mean if your data is reproducible?reproducible?

Why are these qualities important to Why are these qualities important to scientists?scientists?

Calculating SpeedCalculating SpeedSpeed = distance traveled / timeSpeed = distance traveled / time

What units did we use in this lab?What units did we use in this lab?

What units would you use to measure the What units would you use to measure the speed a car travels?speed a car travels?

What units would you use to measure the What units would you use to measure the rate at which your hair grows?rate at which your hair grows?

Speed = Distance/TimeSpeed = Distance/Time►What is the speed of a car that travelsWhat is the speed of a car that travels

100 miles in 2 hours?100 miles in 2 hours?►50 MPH50 MPH

►What is the speed of a car that travels What is the speed of a car that travels 30 kilometers in 1/2 hour?30 kilometers in 1/2 hour? 60 km/h60 km/h

►What was the tested variable?What was the tested variable?The height of the release of the The height of the release of the cart. This was the variable we cart. This was the variable we changed or manipulated.changed or manipulated.

►What variable was time?What variable was time?►Was there a different controlled Was there a different controlled

variable in part B?variable in part B?

Discuss Analysis 1-3 with your Discuss Analysis 1-3 with your groupgroup

1.1. According to your data from part A, what According to your data from part A, what is the speed of the cart?is the speed of the cart?

2.2. According to your data from part B, what According to your data from part B, what is the effect of release height on speed?is the effect of release height on speed?

3.3. List some common units for speed. Why List some common units for speed. Why are there so many different units?are there so many different units?

Analysis Question #3Analysis Question #3►List some common units for speed. Why List some common units for speed. Why

are there so many different units?are there so many different units? miles per hour (MPH)miles per hour (MPH) kilometers per hour (kph or km/h)kilometers per hour (kph or km/h) meters per second (m/s)meters per second (m/s) Different speed units are used because there Different speed units are used because there

are many different units for distance and are many different units for distance and time, and some units are more convenient to time, and some units are more convenient to use than others in different situations.use than others in different situations.