# Stopping Distance

 Materials: Computer and School Network Time Allotment: 3 Class Days

### Purpose:

The purpose of this lab is to analyze the variables which effect the stopping distance of a skidding car and to analyze the distance-velocity relationship for a decelerating object.

### Procedure:

To begin this lab:

1. Log on to the student server in the usual manner
2. Open the Multimedia folder; then open the Hypercard application.
3. Once the Hypercard is opened, chose Open... from the File menu.
4. A directory dialogue box should appear. Navigate through the Physics Stacks directory and find the file titled Stopping Distance; open this stack by double-clicking on its icon.
5. Click anywhere on the first card in order to navigate to the simulation card.

Running the Simulations:

Near the bottom of the monitor are three input fields for entering values for the mass, speed, and acceleration of a car which is braking to a stop. Clicking on these fields allows the user to enter desired values. Accepted values of mass, speed, and acceleration are:

• Mass: 600 kg to 1400 kg
• Initial Speed: 10 m/s to 45 m/s
• Acceleration: -7 m/s/s to -10 m/s/s

Clicking on the Run Simulation button will run the simulation with the current values of mass, speed, and acceleration. Once the car reaches the 0-mark, the brakes are applied and the car slows down with the designated acceleration. As the simulation runs, the car will leave a trail of dots to mark its position at regular time intervals - say, every one-half second. The grid below the car can be used to determine the distance which the car moved while braking. Your task involves determining which factors effect the stopping distance of the car and to analyze the relationship between stopping distance and speed. To accomplish this task you will have to run multiple simulations and systematically vary one of the quantities at a time. Record all your data in the tables below. To assist in the data collection process, you may want to first read the Analysis questions.

### Data Table:

Part 1: Effect of Mass on Stopping Distance

 Init. Speed = ___________ m/s Accel'n = __________ m/s/s

 Mass (kg) Stopping Distance (m) __________ __________ __________ __________ __________ __________ __________ __________ __________ __________ __________ __________ __________ __________

Part 2: Effect of Acceleration on Stopping Distance

 Init. Speed = ___________ m/s Mass = __________ kg

 Accel'n (m/s/s) Stopping Distance (m) __________ __________ __________ __________ __________ __________ __________ __________ __________ __________ __________ __________ __________ __________

Part 3: Effect of Initial Speed on Stopping Distance

 Mass = ___________ kg Accel'n = __________ m/s/s

 Init. Speed (m/s) Stopping Distance (m) __________ __________ __________ __________ __________ __________ __________ __________ __________ __________ __________ __________ __________ __________ __________ __________ __________ __________

### Analysis:

1. What effect (direct, inverse or none) does varying mass have upon the stopping distance of the car? ________________ Support your answers by making actual reference to the collected data.

2. What effect (direct, inverse or none) does varying acceleration have upon the stopping distance of the car? ________________ Support your answers by making actual reference to the collected data.

3. What effect (direct, inverse or none) does varying initial speed have upon the stopping distance of the car? ________________ Support your answers by making actual reference to the collected data.

4. Does the relationship between initial speed and stopping distance appear to be linear to the first power or linear to the second power?________________ To find out, use the Graphical Analysis program (on the school's server) to plot distance vs. speed (speed is plotted along the horizontal axis). Once the data is entered, and the statistics have been turned on, make a note of the COR. Then raise speed to the second power. (Consult the Graphical Analysis Manual if necessary.) Compare the COR of the new graph with that of the old. Print your two graphs (with Statistics showing) and include with your lab report. Now make an exhaustive explanation of the original question.

5. Express your understanding of the relationship between the initial speed and the stopping distance by completing the following statements; fill in the blank with words such as doubled, tripled, quadrupled, halved, quartered, increased by a factor of 6, decreased by a factor of 12, etc.

As the initial speed of a car is ...

6. ...doubled, the stopping distance will be _______________________.
7. ...tripled, the stopping distance will be _______________________.
8. ...quadrupled, the stopping distance will be _______________________.
9. ...halved, the stopping distance will be _______________________.
10. ...decreased by a factor of 3, the stopping distance will be _____________________.

### Conclusion:

Use several well-written and complete sentences to summarize the priniciples of this lab, identifying the variables which effect the stopping distance of a skidding car and discussing the quantitative relationship between the stopping distance and the initial speed.