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TeachEngineering Hands-on Activity:

*A Shot Under Pressure

TeachEngineering Digital Library:

teachengineering.orghttp://www.crt.state.la.us/parks/ibyusegne.aspx

TeachEngineering Digital Library

• The TeachEngineering digital library provides free, teacher-tested, standards-based engineering content for K-12 teachers to use in science and math classrooms.

• Engineering lessons connect real-world experiences with curricular content already taught in K-12 classrooms.

• Mapped to educational content standards, TeachEngineering's comprehensive curricula are hands-on, inexpensive, and relevant to children's daily lives.

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General Advice• Be prepared! Do each activity beforehand

• Make sure all materials are available

• Keep students on task

• Follow the time frame

• Be flexible

• Have Fun!!

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http://commons.wikimedia.org/wiki/File:Watergun.jpg

A Shot Under Pressure• Fluid Dynamics, Bernoulli’s Equation

• Engineering focus: o Engineering Research/Analysis

• Students use their understanding of projectile physics and fluid dynamics to find the water pressure in water guns.

• By measuring the range of the water jets, they are able to calculate the theoretical pressure.

• Students create graphs to analyze how the predicted pressure relates to the number of times they pump the water gun before shooting.

• Learning objectives:o Use projectile motion physics to determine the initial velocity of a projectile

launched horizontally.

o Use Bernoulli's equation to find the pressure of a fluid.

o Collect, record and analyze data to determine relationships among variable.

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Full Activity on TeachEngineering

A Shot Under Pressure• Suggested time: 120 minutes (can be modified for 60

minutes)

• Suggested group size: 3 students/group

• Materials o Each group needs:

• water gun with a pumping mechanism (for example, Super Soaker Water Blasters; available at stores such as Target, Kmart, WalMart or online; ~$10 each); ask students to bring in their own, if possible

• moveable desk or table, on which to mount the water gun

• duct tape

• tape measure, long enough to measure 35+ feet (11+ meters)

• (optional) chalk or tape, to mark off every 10 meters of the shooting range

• pen or pencil

• Take Your Best Shot Worksheet , one per student

• (optional) Evaluation & Enhancement Worksheet , one per student

• (optional) computer with Microsoft Excelo For the instructor:

• Take Your Best Shot Worksheet Answers

• Evaluation & Enhancement Worksheet Answers

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http://www.teachengineering.org/view_activity.php?url=collection/cub_/activities/cub_bernoulli/cub_bernoulli_lesson01_activity1.xml

A Shot Under Pressure

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Engineering Connection (Real World Application):• Biomedical/Civil Engineering

• When engineers design water amusement park rides, water fountains, or anything that involves shooting water, they use a similar modeling process to determine where water jets will land; this ensures the safety and best experience for its users.

• More generally, Bernoulli's equation is used by any engineer working with fluids.

• For example:

o Biomedical engineers use this principle to model the flow and pressure of bodily fluids

o Civil engineers use it to determine the size of pipes needed to get water to people's homes and workplaces, or run industrial processes.

A Shot Under Pressure

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Vocabulary Terms

Definitions/Equations

incompressible A fluid that does not compress, or in other words it has a constant density.

inviscid Effects from the viscosity of a fluid are ignored.

range Horizontal distance traveled by a projectile.

streamline A line tangent to the direction of flow in a fluid that illustrates how fluid flows around an obstacle.

viscosity The internal friction in a fluid. Fluids with high viscosity are thick and slow (such as molasses), while those with low viscosity (such as alcohol) are thin and fast.

A Shot Under Pressure

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Activity Background: Bernoulli’s Equation

o An important expression that relates pressure, height and velocity of a fluid at one point along its flow.

o A fluid's pressure decreases as its velocity increases; The Bernoulli equation puts this relationship into mathematical terms and includes a term for fluid height.

o Example: Think of water moving down a water slide. At the top (where you load), the water is slow moving, pushed only by the water behind it. When the slide drops, the water rushes down quickly, increasing speed as it falls. Thus, the velocity is also affected by gravity through height.

o Bernoulli’s equation: , where = velocity, = fluid density, = relative height, and = pressure

A Shot Under Pressure

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Activity Background: Finding the Pressure in a Water Gun

o Bernoulli's equation can determine the pressure inside the water gun, but first you have to know how fast the water coming out of it is moving - velocity.

o Water leaves the water gun in the horizontal direction, so its total velocity can be reduced to horizontal velocity (). A simple relationship relates the horizontal velocity () to the distance () it travels in a certain amount of time ():

Equation 1

o The distance can be measured, but we need to calculate time using another equation that relates time to the initial and final vertical positions of the water ( and ), the initial vertical velocity (), and the vertical acceleration, :

Equation 2

o In this problem, Equation 2 simplifies to:

Equation 3

o Once time () is solved for, it can be plugged into Equation 1 to solve for velocity ()

A Shot Under Pressure

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Activity Background: Finding the Pressure in a Water Gun (cont.)

o Once velocity is found, we can solve for pressure using Bernoulli's equation. We can set the Bernoulli equation at two points equal to each other as shown in the equation below:

o For this particular problem, two useful points to choose are the inside of the gun (position #1) and the outside of the gun at the nozzle (position #2). These points are chosen because we know that the velocity of the water inside the gun () is initially zero, and that the pressure outside the gun () is the atmospheric pressure (~101,000 Pa). The density () is the density of water, and the relative heights ( and ) are equal if the gun is level. Using algebra, the pressure inside the water gun is easily solvable!

http://www.teachengineering.org/view_activity.php?url=collection/cub_/activities/cub_bernoulli/cub_bernoulli_lesson01_activity1.xml

A Shot Under Pressure

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Before the Activity: o Gather materials. If possible, ask students to

bring their own super soaker water guns from home.

o Make copies of the Take Your Best Shot Worksheet and (optional) the Evaluation & Enhancement Worksheet.

o Find an appropriate location to shoot the squirt guns. It is best to secure a relatively open space with access to water and a dry concrete surface (to better see where water lands).

o Set up a table or desk so it is level, and mark off with chalk or tape the distance from the table every meter for ~10 meters.

http://commons.wikimedia.org/wiki/File:Super_Soaker_CPS4100.jpg

A Shot Under Pressure

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With the Students: 1. Class Discussion:

Most popular water guns today use a hand pump to build up air pressure and shoot water out of a tube, often in order to soak your friends and family while looking totally awesome. How much pressure do you think it takes to have this fun? How would one even go about calculating that? The following activity answers those questions, but first, what do you think?

2. Hands-On Experimentation - Prep! Have students do the following:

a. Fill your water gun with water. Pump it a couple of times and shoot it, then top it off. So the water gun works properly, leave a small amount of air in the tank.

b. Mount your water gun on a sturdy surface approximately a meter above the ground. The gun should be mounted on its side and secured with duct tape. Once secured, make sure you can still squeeze the trigger and move the pump.

c. Measure the height of the nozzle above the ground.

d. Designate one group member to be responsible for marking where the water lands.

A Shot Under Pressure

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With the Students: 3. Hands-On Experimentation - Testing! Have students do the following:

a. Pump the water gun the number of times you have decided for your first trial (see data table below), and shoot the water. Hold the trigger until the water has stopped coming out, to ensure that no pressure is left in the chamber.

b. Measure the distance between the nozzle and where the water lands. Measure the height of the nozzle above the ground.

c. Repeat a. and b. 2 times to find the maximum distance for the number of pumps.

d. Repeat a. – c. for each trial and complete the data table below.

A Shot Under Pressure

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With the Students: 4. Data Analysis:

a. Have students create a graph of the maximum distance traveled v. the number of pumps using the data they recorded in their data table.

b. Have students calculate pressure for each trial.

• This is very dependent on students’ level of comfort with algebra!

• Recommended: Go through the sample calculations with students that is provided on the Take Your Best Shot Worksheet Answers.

• If students are not comfortable doing the calculations, use two data points from a group (for example, 3 pumps and 9 pumps) and work through the calculations as a class to find the pressure in each case. Discuss the relationship between the number of pumps, the pressure and the distance the water traveled.

• Another option: if all groups are using the same type of water gun, assign each group a trial (number of pumps) and have that group calculate the pressure. Have groups share results with the class, and then each group can graph the pressure v. the number of pumps.

c. Discuss results together as a class and re-emphasize the engineering connection (biomedical engineering, civil engineering).

A Shot Under Pressure

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Teaching tips: o Emphasize the science concepts, vocabulary, and engineering connection;

reinforce these throughout the activity.

o As mentioned on the last slide, go through the sample calculations with students that is provided on the Take Your Best Shot Worksheet Answers.

o Depending on your water gun design, it’s best to place the water gun sideways on a flat table to ensure a horizontal shot and easy trigger access.

o One or two pumps might not yield any results depending on the type of water gun used. If this is the case, have students start their data collection at the first number of pumps that yield results and perform trials at up to ten pumps beyond that.

o It is important to leave some air in the water tank to make sure the water gun works properly.

o If holding the trigger until the water stops shooting does not work, the depressurization of the chamber between trials can be achieved by opening the water tank, thereby depressurizing the system.

Activity Takeaways• Teambuilding skills

o Working together on experimentation, collecting data, performing calculations and analyzing results

• Engineering skillso Engineering Research and Analysis: conducting experimental

trial, gathering results, analyzing data, relating results to real world engineering (biomedical and civil engineering)

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• Encouragement through hands-on learningo This activity is very hands-on, and allows

students to use water guns to collect and analyze data in order to learn about science and engineering concepts.

• Motivation through having funo Introduce the activity as a fun learning

experience!

TeachEngineering Contact

Information• TeachEngineering: http://www.teachengineering.org/

o over 1,200 standards-based engineering lessons and activities

• Carleigh Samson, TeachEngineering Editoro carleigh.samson@colorado.eduo 303.492.6950

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