What limits the speed of a car, boat or a transport truck?

Introduction: (Initial Observation)

Making cars and boats that drive faster has been a continuous challenge since such machines were invented. Even airplanes have speed limits. What forces limit the speed is the subject of this project. For a car driving in a flat – open road, if the driver stop pushing the gas pedal, or runs out of gas, the car comes to a stop after a short while. What makes the car stop? Why doesn’t it keep moving with the same speed? What force is slowing down and stopping a moving car?

Most cars can drive as fast as 140 miles per hour (220 Kilometers per hour). Why can’t they go faster? Can you make a car that drives 1000 miles per hour or 2000 miles per hour? Is such thing possible? In this project we will study what limits the speed.

Information Gathering:

Find out about air friction forces and water friction forces. Read books, magazines or ask professionals who might know in order to learn about the effect of such forces and how they may be reduced or increased. Keep track of where you got your information from.

Following are samples of information you may find.

Even though you cannot see them, air molecules (a mixture of gases, mainly nitrogen and oxygen) are just like all other molecules inasmuch as they have mass and occupy space. Anything moving through air must push the molecules out of the way.

The faster the object moves, the faster the air molecules are encountered and the greater are the number to be pushed aside. This requires a larger force that necessary when the object is moving slowly. Consider swimming: The faster you swim, the harder it is to push the water molecules out of the way. More…

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

1. What is the effect of vehicle size on air resistance?

Additional Possible questions:

2. What is the effect of speed on air resistance?

3. Effect of vehicle design in air friction forces?

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

This sample shows how to define variables for question 1.

Independent variable (also known as manipulated variable) is the vehicle size.

Dependent variable (also known as responding variable) is the free run distance of the vehicle.

Constants are the mass and body materials of the vehicle.

Controlled variables are environmental factors such as air temperature and wind. Do all the experiments indoor to protect your experiment setup from wind and temperature changes.

This sample shows how to define variables for question 2.

Independent variable (also known as manipulated variable) is the speed of vehicle.

Dependent variable (also known as responding variable) is the time it takes for the speed of vehicle to reduce a certain amount. Less time indicates more friction.

Constants is the vehicle.

Controlled variables are environmental factors such as air temperature and wind. Record environmental conditions to show that they have not been affecting your results.

Hypothesis:

Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis. This is a sample hypothesis for question 1:

My hypothesis is that air friction will limit the speed of cars, trucks and other objects moving in the air. If we increase the size of a vehicle, then more air molecules will hit the front of the car and more air friction will form and vehicle will travel less.

This is a sample hypothesis for question 2:

My hypothesis is that air friction increases with any increase in the speed of the vehicle. If the vehicle is driving faster, it will take less time for the vehicle to reduce its speed by a certain amount.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1:

Introduction: In this experiment we test the effect of vehicle size on the amount of air friction forces that can bring a moving vehicle to stop.

1. Use a piece of wood or heavy cardboard to make a slope track with the slope of about 30 degrees from the ground. The recommended length of the track is at least about 2 feet or 60 cm. The width of about 5 inches or 12 cm is sufficient.
2. Make a simple toy car with no body. A 2″x4″ block of wood and 4 wheels are enough for the car. The block of wood is the chassis of the car.
3. Make 3 different car bodies that can be mounted on the chassis with the help of small pins or some adhesive tape. Make sure all three cars will have the same weight. One way to do that is using same size papers in making the cars and insert the left over paper of each car into the same car.
4. label the cars with small, medium and large accordingly.
5. Place the car chassis on the top of the slope and let it slide down the track and then run across a smooth floor.
6. Measure and record the distance the car travels from the bottom of the slope.
7. Repeat the steps 5 and 6 two more times and record the distances in your results table.
8. Mount the small car body on the chassis and repeat the same tests with the small car. Record your results in the results table.
9. Disconnect the small car from the chassis and mount the medium car. Repeat the slope test again with the medium car 3 times and record the results.
10. Disconnect the medium car from the chassis and mount the large car. Repeat the slope test again with the large car 3 times and record the results.

Your data/ results table will look like this:

For the Chassis, small car, medium car and the large car calculate the average distances for three trials and write the result in the last row of your results table. To calculate the average you can add three numbers and then divide the total by 3.

Make a graph

You can make a bar graph to visually present your results. Make 4 vertical bars, one for chassis, one for small car, one for medium car and one for the large car. The height of each bar will be the average distance that car traveled.

Some Pictures/ Diagrams for this experiment:

Experiment 2:

Introduction: In this experiment we test the effect of vehicle speed on the amount of air friction. As an indication of the air friction we will measure the speed reduction time. This experiment needs an actual vehicle drove by an adult and the support of parents. Students will only record the data and report the results.

Materials:

• Stopwatch
• Vehicle
• Adult driver
• Flat road or open space with no traffic
• Good weather with no wind

Procedure:

1. Drive the vehicle to the speed of 10 miles per hour.
2. Move the vehicle to Neutral and start timing. Do not use the break. Stop timing as soon as the vehicle comes to a full stop (speed 0).
3. Record the initial speed (10 miles/hour) and the time it took for the vehicle to stop.
4. Drive the vehicle to the speed of 20 miles per hour.
5. Move the vehicle to Neutral and start timing. Do not use the break. Stop timing as soon as the vehicle speed goes down to 10 miles/hour.
6. Record the initial speed (20 miles/hour) and the time it took for the vehicle to slow down to 10 miles per hour.
7. Drive the vehicle to the speed of 30 miles per hour.
8. Move the vehicle to Neutral and start timing. Do not use the break. Stop timing as soon as the vehicle speed goes down to 20 miles/hour.
9. Record the initial speed (30 miles/hour) and the time it took for the vehicle to slow down to 20 miles per hour.
10. Repeat each of the above measurements two more times and record your data in a table like this.

m/h = Miles per hour

After doing your experiment trials and entering your data in the table, calculate the average of speed reduction time for each of the initial speeds and write them in the last row of your results table.

Analyze the results and draw a conclusion.

Based on your results conclude if the air resistance forces increase when the speed is higher.

Make a graph

You can make a bar graph to visually present your results. Make 3 vertical bars, one for each initial speed. The height of each bar will be the average time it took for the speed to reduce by 10 m/h.

Materials and Equipment:

This is a sample list of materials and equipment. The final list of materials and equipment in your project may be different from this list.

1. Wood board 24″ x 5″ x 1/2″ used as slope
2. Wood board 4″ x 2″ x 1/2″ used as the car chassis frame
3. 4 wooden or plastic wheels
4. 4 small nails to attach the wheels to the chassis frame
5. Carton box 12″ x 12″ x 12″ to hold the top of the slope
6. Adhesive tape (used to connect the slope to the box and to the floor and also used in construction of the car bodies.)
7. 4 sheets of construction paper (used to construct the model cars)
8. Measuring tape
9. Pencil, ruler, pair of scissors

You may modify an existing toy car instead of making a wooden car cahssis.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Your results in this project will include a completed results table as shown in the experiment section and a bar graph.

Calculations:

You will calculate the average travel distance for each size car.

Summery of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

A result summery table does not include all the initial measurements.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Does the results support your hypothesis? Did the larger car travel less? Are larger cars subject to more air friction?

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

How does the speed of a vehicle affect the air friction forces?

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

List of References

1. Air resistance also known as drag.
2. Newton’s Law. Elephant and Feather free fall.