Note Card Quiz Name_____________ Date _____ Period ___ Activity 54, Analysis #3

Major Concepts: ► Activity 56  There was a direct relationship between the amount of kinetic energy put into the system and the amount of energy transformed (thermal energy). This was measured by an increased temperature. ► Activity 58  The sun is a major source of energy for changes on earth’s surface.  Energy can be transferred, however, it can never be destroyed.

Major Concepts: ► Activity 73  Making decisions often involves trade-offs----- giving up one thing to gain another.  The potential for accidents and the existence of hazards impose the need for injury prevention and the need to understand the physics of how a car moves (force and motion)

What factors can contribute to a car accident?

Speed ► Speeding or going too fast ► In the United States, car speed is typically measured in mph. ► km/h is used for car speed in other countries. ► Scientists often measure everyday speeds in m/s. ► Today, we will measure speed in cm/s.

Title: Title: Measuring Speed Activity 74

Background Information: ► Speed   An object in motion takes time to change its position. Speed is the measurement of the rate of change in position and can be linear or rotational. The units for speed are a distance or an angle per unit of time, such as miles per hour or degrees per second. ► Velocity   Speed (s) and velocity (v) are related concepts but are not the same thing. The velocity of an object includes both its speed and its direction.

Speed vs. Velocity ► What is the difference? The velocity of an object includes both its speed and its direction.

More vocabulary ► tested variable: the variable that is manipulated (changed) in an experiment. Also called independent variable. ► controlled variables: the variables that are not changed in an experiment. ► controlled variables: the variables that are not changed in an experiment. ► responding variable: the variable you are measuring in an experiment. Also called dependent variable.

Read E-7 Part A Problem: How can you measure the speed of a moving cart? Hypothesis Part A: If you ______________, then you can ______________________.

How do people measure speed? ► Speedometer ► Radar Gun ► Total Distance/Total Time READ THE PROCEDURE!

Level portion of the track

Procedure ► Step #8 – Why do you use three trials? ► Watch for ERROR. What is this?  Timing errors may cause the time to be too long or too short.  You may stop the watch too soon, and sometimes too late.  Your reaction time may effect the timing.  Taking the average of 3 trials can limit the error.  You may need to do an addition trial if one is too far off from the others.

Minimize Errors ► Release the cart the same way each time. ► Try to get data that is ACCURATE and REPRODUCIBLE. ► If you get 10 cm/s, 11 cm/s, and 25 cm/s, you may want to redo the third trial. ► Put a book to stop the cart. The cart SHOULD NOT roll off the table.

Data/Evidence: Trial Distance (cm) Time (s) Speed (cm/s) Always include units Average FIX

Speed = Distance/Time ► 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 1/2 hour?  60 km/h Is read “per” and means to divide

Part A Discussion ► What is a variable? A variable is what we change, measure and control in an experiment. They are the factors that influence the speed of the cart. ► What variable did we test? There was no tested variable. You did not change or manipulate any factors. ► What variables did we control? the track (release height, angle & surface) the cart’s mass

Part B Problem: What will happen to the speed of the cart if we change the release height of the cart? Hypothesis: If you lower the release height of the cart, then ____________________.

How will you test your hypothesis? How many trials? What are your variables other than height? How many variables are you changing?

Calculating Speed Why did we use the “average value”? What does it mean if your data is accurate? ► the ability to match the actual value What does it mean if your data is reproducible? ► precision is the ability of a measurement to be consistently reproduced Why are these qualities important to scientists?

Calculating Speed Speed = distance traveled / time What units did we use in this lab? What units would you use to measure the speed a car travels? What units would you use to measure the rate at which your hair grows?

► What was the tested variable? The height of the release of the cart. This was the variable we changed or manipulated. ► What variable was time? ► Was there a different controlled variable in part B?

Discuss Analysis 1-3 with your group 1. According to your data from part A, what is the speed of the cart? 2. According to your data from part B, what is the effect of release height on speed? 3.List some common units for speed. Why are there so many different units?

We choose units which are both convenient and “friendly” ► we use numbers between 1 and 1,000 ► minutes or seconds would make some common speeds too small (30 mph = 0.5 miles per minute ► days or years would make them too big (60 mph = 1,440 miles per day

4. What part(s) of your experiment design in Part B: a.increased your confidence in your results? b.decreased your confidence in your results?