Další možné náměty pro skupiny

Balloon Cars

Students will design and build a "car" that will successfully travel 2 meters (minimum) displacement required for which students will earn maximum points.

Design Parameters:

• Car may either have four wheels like a car or three wheels like a tricycle.
• Propulsion can only be provided by the maximum of two nine-inch balloons.
• Wheels may be built out of any available materials of your choosing.
• Students will mount a straw to their car to which the balloon will be attached.
• The body of the car can be built out of any available materials.
• There are no height restrictions.
• Cars cannot be longer than 30 centimeters.

Requirements:

• Cars must have a minimum displacement of two meters.
• Additional points will be awarded for cars traveling further.

Grading:

1. Design: 25 points

• Students using wheels from toy cars or other commercially available wheels will lose 5 points.
• Students using commercially available bodies for their cars (such as toy cars) will lose 5 points.
• Cars longer than 30 centimeters will lose 5 points.
• Students building a car out of readily available materials will earn maximum design points.

2. Performance: 25 points

• Cars having a minimum displacement of 1.0 meters will earn 5 points.
• Cars having a minimum displacement of 1.5 meters will earn 10 points.
• Cars having a minimum displacement of 2.0 meters will earn 15 points.
• Cars having a minimum displacement of 2.5 meters will earn 20 points.
• Cars having a minimum displacement of 3.0 meters will earn 25 points.

3. Experiment Design: 25 points

• Students must submit (individually) an experimental procedure describing what steps they must take to collect data.
• All data must be listed.

4. Questions: 25 points

Questions are worth five points each. Students must submit their answers to questions individually.

• Describe your initial design. Describe how your design evolved into the one that you used. What did you alter about your original design and why?
• Describe the motion of your car. Did it run at a constant speed or accelerate constantly?
• Why do you feel that your car ran at constant speed or accelerated constantly? (In your explanation describe the forces involved.)
• Calculate the average speed of your car. State the distance your car went and the time that elapsed.
• Apply Newton's Third Law to your car.

Zdroj: GoToScience:Lesson Plans With Fun Labs & Activities for High School Science.

Energy Transfer

How powerful are your students? How can we measure their power? Here is one way, which helps them understand different forms of energy.

Objectives:

• To measure the energy a student can put into a small volume of water.
• To explore different ways heat can be added to water.
• To introduce units of heat energy, and relate them to units of electrical energy, and ultimately to -student power-.
•  

Materials; for each pair of students:

• A standard-sized test tube with a stopper.
• Stop watches
• Thermometer

Procedure

• 1. Students work in pairs. Each pair is given a test tube into which they pour 10 to 20 ml of water.
• 2. They should measure and record the initial temperature and mass of their water. (1 ml = 1gram)
• 3. When the signal is given, students begin doing whatever they wish with their test tube to warm it up. They can shake it, rub it, sit on it, whatever they want, so long as they only use their body.
• 4. After five minutes time is up! Take and record the final temperature.

Calculations:

1. The heat gained by the water is found by subtracting the initial temperature from the final temperature (Tf - Ti) The temperature change is used to find the change in heat energy, which is measured in calories.

2. The temperature change is converted into calories by multiplying each degree gained by the number of grams of water. If 10 g of water gained 8 degrees, then 80 calories of heat was added to the water. (Note: Calories in food are actually Kilocalories, which are 1000 calories each).

3. Work is defined as a force causing movement. The work done in raising the temperature of water can be found by multiplying the calories added to the water by 4.19 joules (joules is a unit of work). 80 calories X 4.19j = 335.2 joules.

5. Power is defined as work over time, and is expressed in watts (335.2 j /300 seconds = 1.12 watts)

Let's take a look at the last step, and what it is really saying. Since the student in the example did 335 joules of work over 300 seconds, he did 1.12 joules of work each second, which is then defined as 1.12 watts. Relating this to the more familiar electrical watt, a 100 watt bulb performs 100 joules of work each second.

Extension:

You can finally convert watts to kilowatts, then to kilowatt hours, and see what we pay for electrical power. The electric company sells us power by the Kilowatt hour (Kwh), meaning 1000 watts of power in use for an hour. In other words, if a 100 watt bulb is on for ten hours, you have used one kilowatt hour. A Kwh might cost $.25. If each student in your class is capable of generating 1 watt of power, then 33 of them would need to work for 30 hours to produce the equivalent energy contained in one kilowatt hour! (1 watt x 33 x 30.3 = 1 kilowatt hour) Maybe electricity is not so expensive after all!

Physical Properties of Food Wraps

What We'll Study...
The mechanical properties of polymers in the form of food wraps. Properties include tensile strength, elongation, flexural strength, and impact resistance.

Did You Know...
Analytical chemistry is important to industry because the accurate measurement of quantities, composition, and properties is critical to the market success of products. These measurements are usually performed on highly sophisticated and complex instruments that are not available in the high school laboratory. This lesson contains simulations of analytical work to give you an appreciation for the technical work needed by industry. You should become familiar with the terms "accuracy" and "precision" as the work is performed. For all mechanical properties testing of polymers, a wide spread of values is obtained. Therefore, it is necessary to test several samples and calculate an average for each property.

Among the more important mechanical properties of polymers are tensile strength, elongation, flexural strength, and impact resistance. A large number of standard tests have been developed. Standards are set by the American Society for Testing Materials (ASTM).

To measure tensile strength, a test specimen of uniform cross-section is clamped at each end and stretched until it breaks. Tensile strength is defined as the stress force necessary to break the sample at a constant rate of stretching. It usually varies from about 1,000 to 12,000 pounds per square inch (psi) for most common commercial polymers. These values would be equal to 6.9 to 82.8 megapascals (MPa) or newtons/square meter (N/m²).

Elongation is the increase in length of a sample at the breaking point. Elongation is associated with the uncoiling of polymer molecules and their movement relative to other molecules. Highly crosslinked polymers have a low elongation relative to linear polymers. Elongation can vary widely among polymers and is usually expressed as a percent of the original length of the sample.

Flexural strength is measured by supporting a sample test bar of uniform cross-section at each end, in a horizontal position. The sample is then subjected to a vertical stress until it yields or breaks. Most common polymers have flexural strengths ranging from 3,000 to 20,000 psi (20.7 to 138.9 MPa or N/m²). Crosslinked polymers are more rigid and have a higher flexural strength than linear polymers.

Impact resistance is a measure of the toughness of a polymer. It can be determined by striking a vertical sample with a weighted pendulum and measuring the distance the pendulum travels after the sample breaks. Values for impact resistance for common polymers range from 0.5 to 10 foot-pounds per inch (0.1 to 0.2 J/cm²).

OBJECTIVES

To test the physical properties of various food wraps and compare polymer-based wraps to nonpolymer-based wraps.

MATERIALS (PER LAB STATION)

• 5 (2-inch x 8-inch) strips of the following food wraps:
  • polyvinylidene chloride film (e.g., Saran Wrap* Brand Plastic Film)
  • polyethylene film (e.g., Handi-Wrap** Plastic Film)
  • waxed paper
  • aluminum foil
• 2 ring stands and a crossbar with 2 clamps
• 1 (10 N) spring scale
• 1 wooden handle hammer
• 1 screw eyelet with a diameter fitting a crossbar
• 1 coffee can (one end open)
• 1 (30 cm) metric ruler
• duct tape
• 1 set of weights (0.2 N to 10 N)
• 1 pair of scissors

*Trademark of the Dow Chemical Company
**Trademark of DowBrands

SAFETY AND ENVIRONMENTAL CONCERNS

• Goggles should be worn.
• Dispose of materials as instructed by your teacher.

PROCEDURES

Tensile Strength

1.     Assemble two ring stands with a crossbar attached horizontally using clamps. Weigh down or clamp the base of the ring stands for stability. See figure below.

2.     Cut 2-inch x 8-inch strips of each type of food wrap and use duct tape to suspend each strip from the horizontal crossbar.

3.     Attach a second piece of duct tape at the base of each sample and pierce a small hole in the tape. A hooked spring scale will be suspended to measure force.

4.     To measure tensile strength, attach a spring scale to the sample. Pull down at a constant rate until the sample wrap breaks. Record the force (N) at the moment of break. This will give a relative value for tensile strength. The final tensile strength value is usually obtained by dividing the force by the cross-sectional area, but in this case the cross-sectional areas of the samples should be fairly uniform.

5.     Collect all the tensile strength data from the class and calculate the average value +/- the deviation.

6.     Repeat the procedure for each type of food wrap.

Elongation

1.     Use the assembled ring stands with a crossbar from the tensile strength procedure above.

2.     Cut 2-inch x 8-inch strips of each type of food wrap and use duct tape to suspend each strip from the horizontal crossbar.

3.     Attach a second piece of duct tape at the base of each sample and pierce a small hole in the tape. A hooked spring scale is suspended to measure force.

4.     To measure elongation, attach a spring scale to a sample and vertically pull down at a constant rate. Record the force (N) at various points of the stretch (cm) until the sample wrap tears. See figure below.

5.     Graph force (N) versus stretch (cm). Determine the slope of the graph to get a relative measure for the elongation of each type of food wrap. Record.

6.     Repeat the procedure for each type of food wrap. Record.

Flexural Strength

1.     Cut a sample of each wrap large enough to be secured over the mouth of an open-ended coffee can.

2.     Mount the sample wrap over the mouth of the can and adhere it to the can with duct tape. Make sure the sample is pulled taut. See figure below.

3.     Add weight (vertical stress) to the center of the sample until the wrap breaks. Record this force (weight) in newtons. It will be used to calculate the flexural strength.

4.     Use p r² to compute the area of a circle in cm² (area of can). Divide the force (N) by the area (cm²) to get the flexural strength.

5.     Repeat the procedure for all sample wraps.

Impact Resistance

1.     Use steps 1 and 2 from the flexural strength procedure to prepare samples for impact resistance. You may need several samples of each wrap.

2.     Construct an impact resistance assembly using a hammer, an eyelet, and the crossbar assembly from the tensile strength procedure. Screw the eyelet into the handle of the hammer such that the crossbar will allow the hammer to swing freely, like a pendulum. See figure below.

3.     Determine the mass of the hammer (in kilograms).

4.     Adjust the height of the crossbar so that the hammer's head strikes the center of the mounted sample on the face of the can, at the base of the hammer's swing.

5.     Pull back the hammer to a set height above the base of its swing. Record height (in meters).

6.     While another lab partner holds the sample still, release the hammer, using caution to avoid injury. Change the starting height until the sample wrap breaks. (A fresh sample should be used for each change in starting height. Otherwise, the sample may be stressed enough by the first hit that a second hit of equal value will break it.) The height will be used to calculate the energy (potential) exerted per sample area required to break the sample. This is a relative measure of the impact resistance of the food wrap.

7.     Calculate the impact resistance (joules per square centimeter) using the potential energy formula (mgD h) divided by area of the hammer head ( p r²).(D=delta; p=pi)

8.     Repeat the procedure for all sample wraps.

DATA AND OBSERVATIONS

Tensile Strength

Data Table

Elongation

Sample Data Table (required for each wrap)

Data Table

 
Flexural Strength

Data Table

Impact Resistance

Data Table

QUESTIONS

1.     Research and describe the differences between linear polymers and branched polymers.

2.     Classify the materials used in this lab as branched polymers, linear polymers, or nonpolymers.

3.     Describe each physical property and relate it to the branched polymers, linear polymers, and nonpolymers. Which wraps had the highest and lowest value for each tested property? Relate these data to the polymer type.

4.     Compare your results to the class results. Explain why many results give a better picture of the "true" result as opposed to only one reading. Relate this to accuracy and precision.

5.     Design a procedure to evaluate a physical property of a new ceramic you have developed for tennis rackets.