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Work-Energy Theorem

  1. Take your Smart Cart out of the box.

  2. Turn it on and open your choice of software: SPARKvue or Capstone.

  3. Wirelessly connect to the Smart Cart.

  4. Change the sample rate of the Smart Cart Position and Force sensors to 40 Hz.

  5. Make a graph of Force vs. Position and another graph of Velocity vs. Time.

  6. Install the hook on the Smart Cart’s force sensor. Without anything touching the force sensor, zero the force sensor in the software.

  7. Put a rubber band on the force sensor hook. Start recording and while one person holds the rubber band in place, the other person slowly pulls the cart back, stretching the rubber band. Then hold the cart in place with the rubber band stretched and stop recording. Do not let go of the cart or rubber band.

  8. Start recording again. Let go of the cart and move the hand holding the rubber band out of the way. Let the cart go up to its maximum speed and then stop recording.

Analysis

  1. Determine the work done in stretching the rubber band by finding the area under the Force vs. Position curve.

  2. Determine the work done as the stretched rubber band pulls the cart by finding the area under the Force vs. Position curve.

  3. On the Velocity vs. Time graph, determine the maximum velocity. Calculate the kinetic energy of the cart and compare to the work done to accelerate the cart.

  4. Why isn’t the work done to stretch the rubber band equal to the work done to accelerate the cart?

Sample Data

The work done loading the rubber band is -1.91 Nm. The work done unloading (when the cart is launched) the rubber band is 0.77 Nm. The resulting kinetic energy of the cart is

KE = ½ mv2 = ½ (0.252 kg)(2.34 m/s)2 = 0.69 J. This is 10% less than the energy available in the stretched rubber band.

The energy stored in the rubber band is less than the work done to stretch the rubber band. Some of that energy goes into heating the rubber band and making the rubber band move.

Static and Kinetic Friction

 

  1. Take your Smart Cart out of the box.

  2. Turn it on and open your choice of software: SPARKvue or Capstone.

  3. Wirelessly connect to the Smart Cart.

  4. Make a graph of Force vs. Position.

  5. Make sure the Smart Cart Force sensor (with the magnetic bumper on it) is not touching anything and then zero the Force sensor in the software.

  6. Set the cart bumper against the book. Start recording. Very slowly push the cart until the book breaks loose and then push it steadily across the table. Stop recording.

  7. Take another run, pushing it at a faster speed once it breaks loose.

  8. Add a second book on top of the first book and repeat.

Analysis

  1. For each run, record the maximum force before the book moved. This is an indication of the static friction. If you can find the mass of the book, you can calculate the static coefficient of friction for the book on the table.

  2. For each run, record the average force while the book was moving. This is an indication of the kinetic friction. If you can find the mass of the book, you can calculate the kinetic coefficient of friction for the book on the table.

  3. What effect does speed have on the kinetic friction?

  4. What changes when the extra book is added? Do the coefficients of static and kinetic friction change?

Sample Data

The average kinetic friction for two books is 6.92 N.

The average kinetic friction for one book going slower vs. faster was 3.35 N compared to 4.19 N. This indicates that the speed does influence the kinetic friction slightly.

Mass of First Book = 1.56 kg

Mass of Second Book = 1.58 kg

For one book:

μs = F/mg = 3.09N/(1.56)(9.8) = 0.2

μk = F/mg = 3.17N/(1.56)(9.8) = 0.2

For two books:

μs = F/mg = 7.11 N/(1.56+1.58)(9.8) = 0.2

μk = F/mg = 6.59N/(1.56+1.58)(9.8) = 0.2

Hooke’s Law

Hooke’s Law states:
where F is the force of the spring, k is the spring constant, and x is the distance the spring has been stretched.

  1. Take your Smart Cart out of the box.

  2. Turn it on and open your choice of software: SPARKvue or Capstone.

  3. Wirelessly connect to the Smart Cart.

  4. Make a graph of Force vs. Position.

  5. Install the hook on the Smart Cart Force Sensor. Make sure the Smart Cart Force sensor is not touching anything and then zero the Force sensor in the software.

  6. Put one end of a spring on the hook and hold the other end stationary with your hand. Move the cart slightly to put a little tension on the spring.

     

  7. Start recording and pull the Smart Cart away from the fixed end of the spring until the spring is stretched out. Then stop recording.

Analysis

  1. On the Force vs. Position graph, apply a linear fit to the straight-line part of the graph.

  2. Determine the spring constant from the slope of the linear fit.

Sample Data


The slope of the graph indicates the spring constant is 6.77 N/m.

Impulse Demonstration

Equipment:

Smart Cart

Accessory Rubber Bumper

Learning Outcome:

A force acting on an object for a period of time imparts an impulse to that object which is defined as a change in momentum.

Experimental Setup:

  1. Take your Smart Cart out of the box

  2. Attach the rubber bumper accessory (included with Smart Cart) to the force sensor on the Smart Cart.

  3. Press the power button on the side of the Smart Cart to turn it on.

  4. In SPARKvue or Capstone, pair the Smart Cart to your computer or device. Here are a couple short videos to help you pair in either software:

    1. SPARKvue: https://www.youtube.com/watch?v=tsdHWu4quNo

    2. Capstone: https://www.youtube.com/watch?v=JGy-UG245lY

  5. In the software, you will need to create a graph of Force vs. Acceleration.

    1. In SPARKvue:

      1. Under “Quick Start Experiments” choose: Impulse

      2. Increase the sampling rate of the Force sensor to 1KHz

    2. In Capstone:

      1. Create two graph displays

      2. Graph 1: [Force] vs. Time

      3. Graph 2: [Velocity] vs. Time

      4. Increase the sampling rate of the Force sensor to 1KHz

You will push the cart into a barrier such that the rubber bumper will collide and bounce the cart off the barrier. A wall, book or other solid vertical surface will work.

Data Collection:

  1. Zero the force sensor

  2. Press the record data button

  3. With the rubber bumper facing towards the barrier, give the Smart Cart a push.

  4. After the Smart Cart has reversed direction, stop data collection.

 

Data Analysis:

  1. On the Force vs. Time graph, use the Area tool to measure the area under the curve. This is the impulse that the Smart Cart experienced.

  2. On the Velocity vs. Time graph, use the Coordinate tool to find the velocity just before the impact of the Smart Cart against the barrier and record this value. This is the Smart Cart’s initial velocity.

  3. Next, using the Coordinate tool find the velocity after the collision with the barrier. Record this value. This is the Smart Cart’s final velocity.

  4. Weigh the cart without any bumper and record the mass. You may also estimate the mass of the Smart Cart to be around 0.250 kg.

Calculate the change in momentum of the Smart Cart: pf – pi

Compare your calculated value to the area under the Force vs. Time graph.

Sample Data:

This data was created with a Smart Cart that measured 0.246 kg, for an error around 1.5%.

Centripetal Acceleration and Force

  1. Take your Smart Cart out of the box.

  2. Turn it on and open your choice of software: SPARKvue or Capstone.

  3. Wirelessly connect to the Smart Cart.

  4. Make a graph of Acceleration-x (from the Smart Cart Acceleration Sensor) vs. Angular Velocity-y (from the Smart Cart Gyro Sensor). Add a second plot area with the Force vs. Angular Velocity-y.

  5. Install the rubber bumper on the Smart Cart Force Sensor. With the cart sitting still, with nothing touching the rubber bumper on the Force Sensor, zero the Acceleration-x, Angular Velocity-y, and the Force in the software.

  6. Set up a board or track on a rotatable chair as shown in the picture. Set the end stop near the end of the track and place the cart’s rubber bumper (Force Sensor end) against the end stop.

    Post

  7. Spin the chair and start recording. Let the chair spin down to a stop and then stop recording.

  8. Apply a curve fit to the data to determine how the centripetal acceleration and force are related to the angular velocity. For the quadratic fit, open the curve fit editor at right in Capstone and lock the coefficient B = 0.

 This forces the fit to Aω2 + C. From the curve fit, what is the radius?

  1. In which direction are the centripetal acceleration and the centripetal force?

Further Study

  1. Move the end stop 5 cm closer to the center of rotation. Repeat the experiment.

  2. Continue to move the end stop closer to the center in 5 cm increments.

  3. How does the centripetal force depend on the radius?

Sample Data

Both the centripetal acceleration and the centripetal force are pointing toward the center of the circle (they are negative) and are proportional to the square of the angular velocity.

a = -0.383ω2 – 0.0530

F = -0.0966ω2 – 0.00596

m = 0.25 kg

F = ma = 0.25(-0.383ω2 – 0.0530) = -0.096ω2 – 0.013

The radius is 0.383 m because a = rω2.

Newton’s Second Law Demonstration

Equipment:

  • Smart Cart

  • Accessory Hook

Learning Outcome:

Forces and Accelerations of objects have a linear relationship that relates the mass of an object being accelerated to an unbalanced force acting on it.

Experimental Setup:

  1. Take your Smart Cart out of the box.

  2. Attach the hook accessory (included with Smart Cart) to the force sensor on the Smart Cart.

  3. Press the power button on the side of the Smart Cart to turn it on.

  4. In SPARKvue or Capstone, pair the Smart Cart to your computer or device. Here are a couple short videos to help you pair in either software:

    1. SPARKvue: https://www.youtube.com/watch?v=tsdHWu4quNo

    2. Capstone: https://www.youtube.com/watch?v=JGy-UG245lY

  5. In the software, you will need to create a graph of Force vs. Acceleration.

    1. SPARKvue: Under “Quick Start Experiments” choose: Newton’s Second Law

    2. Capstone:

      1. Create a Graph Display

      2. Select measurement of [Force] for the y-axis

      3. Select measurement of [Acceleration – x] for the x-axis

      4. In the sampling control panel, press the “Zero Sensor” button

Before you collect data, practice rolling the cart in a forwards and backwards motion by only holding on to the hook. You want to apply a force along the cart’s x-axis, and have the cart roll only along this direction. This is made easier using a PASCO track to keep the cart moving in one direction, but not necessary for the demonstration. (Hint: Try not to wiggle or knock the Smart Cart hook as this will result in extraneous data points.) 

Data Collection:

  1. Press the record data button

  2. Holding only the hook, roll the Smart Cart forwards and backwards in the x-direction.

  3. Repeat this motion a few times to generate enough data points to see the graphical relationship.

  4. Stop data collection

Data Analysis:

  1. Turn on the ‘Linear Fit’ tool

  2. This relationship shows that there is a proportionality constant between the unbalanced force, and the Smart Cart’s resulting acceleration.

  3. The proportionality constant is the mass of the cart.

Add mass to the Smart Cart and repeat data collection for the new system mass.

Sample Data:

This data was created with a Smart Cart that measured .246 kg, for an error around 2%.

Average and Instantaneous Velocity and Speed

  1. Take your Smart Cart out of the box.
  2. Turn it on and open your choice of software: SPARKvue or Capstone.
  3. Wirelessly connect to the Smart Cart. Change the sample rate of the Position Sensor to 40 Hz.
  4. Open the calculator in the software and make the following calculation:
‎speed‎=abs([Velocity, Red (m/s)‎])       with units of m/s
  1. Create a graph of Velocity vs. Time and add a second plot area of speed vs. Time and add a third plot area of Position vs. Time.
  2. Mark a starting point with a piece of tape.
  3. Start recording. Push the cart about 20 cm out and back, ending at the same point where you started.
Analysis
  1. On the Velocity vs. Time graph, find the maximum positive velocity.
  2. What is the instantaneous velocity at the point where you reversed the cart?
  3. What is the average velocity over the entire motion of the cart? Highlight the area of the Velocity vs. Time graph during the time of the motion and turn on the mean statistic.
  4. What is the average speed over the entire motion of the cart? Highlight the area of the speed vs. Time graph during the time of the motion and turn on the mean statistic.
  5. What is the difference between speed and velocity?
Sample Data
The instantaneous velocity when the cart reversed was zero.
The average velocity over the whole trip was zero because we started and stopped in the same place.
The average speed over the whole trip was 0.36 m/s.
Speed is a scalar that is the magnitude of the velocity. Velocity is a vector and has both magnitude (speed) and direction.

The Differences Between Velocity and Acceleration

  1. Take your Smart Cart out of the box.

  2. Turn it on and open your choice of software: SPARKvue or Capstone.

  3. Wirelessly connect to the Smart Cart.

  4. Change the sample rate of the Smart Cart Position sensor to 40 Hz.

  5. Set up a graph of Velocity vs. Time and Acceleration vs. Time using the Position sensor’s Velocity and Acceleration.

  6. Make an inclined plane by placing the top edge of one textbook on top of a second textbook.

  7. Put the Smart Cart at the bottom of the incline, with its force sensor end oriented up the incline.

  8. Start recording and push the cart so it just barely reaches the top of the incline and then rolls back down. Stop recording when it gets back down.

  9. Examine the graphs and determine where the cart is:

    1. going up the incline.

    2. going down the incline.

    3. at the top of the incline.

For each of these cases, is the velocity positive, negative, zero, and/or constant? Is the acceleration positive, negative, zero, and/or constant?

  1. When the cart is going up the incline, which direction is the velocity? Which direction is the acceleration? Is the cart accelerating or decelerating?

  2. When the cart is at the top of the incline, the velocity is zero. Which direction is the acceleration? Is the cart accelerating or decelerating?

  3. When the cart is going down the incline, which direction is the velocity? Which direction is the acceleration? Is the cart accelerating or decelerating?

  4. On the Velocity vs. Time graph, find the slope of the straight-line portion. Compare this to the acceleration on the Acceleration vs. Time graph.

Sample Data

When the cart is going up the incline, the velocity is positive (up the incline) while the acceleration is constant and negative (down the incline). The cart is decelerating.

When the cart is at the top of the incline, the velocity is zero while the acceleration is constant and negative (down the incline). The cart is accelerating.

When the cart is going down the incline, the velocity is negative (down the incline) while the acceleration is constant and negative (down the incline).

The slope of the Velocity vs. Time graph is -1.57 m/s2. The average acceleration from the Acceleration vs. Time graph is -1.577 m/s2, which is 0.6% different from the slope.

Give a scientist a sensor…

(a reflection on hosting a pro-d event)

I recently hosted my first ever professional development event.  Usually, at the local level, there aren’t many opportunities for science types.  There just aren’t enough of us and we specialize so there isn’t much common talk beyond ‘how can we get the students to love and learn science more?’.  That is why I went out of comfort zone to host an event on sensors.  I’m still not an expert on my physics equipment from PASCO let along the sensors for the other branches but I thought it was worth the shot.

How do I do a pro-d event that engages the audience?  How could I hook the teachers in attendance?  The answer was easy.  Not for me to stand there and talk at them.  No!  They needed to do science!  They needed to use the sensors.  So, that’s what we did.

I set up several stations in my room.  One for physics, one for bio, one for chem and outside for earth science.  Each station required the use of an appropriate sensor (motion, CO2, pH and weather) and a task.  I gave them as little instruction as possible beyond how to use SPARKVue.  I wanted them to experience what their students would.

I expected only my department to show up.  That is still 13 people.  I had middle school and elementary teachers show up as well.  How would they do?  The hours flew by.  I didn’t need to worry about filling the time; we needed more.  There was a buzz that you don’t hear at staff meetings.  They were engaged.  They were loving it.  They were hooked on sensors.

What I loved most was the talk on how they could use it for their classes.  I wanted to get their ideas because they would know better than I.  Every teacher left with an idea on how the sensors could be used…if only we had more.
When the day was over I was asked to host more of these.  It was very easy to say yes.

Explorations in Photosynthesis and Respiration

Originally posted on PASCO’s Blog. Blog is written by Bruce Taterka a teacher at West Morris Mendham High School in New Jersey

PASCO’s Wireless CO2 Sensor provides a powerful opportunity for students to explore the effects of photosynthesis and respiration in their local environment. This blog will describe how students can use a “Pretzel Barrel CO2 Chamber” to design experiments to measure rates of photosynthesis and respiration in a wide variety of settings and circumstances.

Background

Soil plays an important role in the carbon cycle and global climate because it acts as a carbon sink, sequestering CO2 from the atmosphere in the form of organic matter. The upper layers of soil contain organic matter that is actively decomposed by the soil community: microbes, insects, worms and other animals.

While respiration by soil organisms decomposes organic matter and releases CO2, the plant community is photosynthesizing and taking in CO2 from the atmosphere. So in this part of the earth’s carbon cycle, CO2 is moving in two directions – into the atmosphere from soil, and out of the atmosphere into plants. We refer to this transfer of carbon as “CO2 flux.” With PASCO’s Wireless CO2 Sensor, students can explore the carbon cycle, plant and soil biology, and climate change by measuring CO2 flux.

The rate of CO2 flux depends on a wide variety of factors. For soil, the rate of CO2 production may be affected by:

  • The content and type of organic matter in the soil
  • Temperature
  • Moisture
  • Sunlight
  • Soil chemistry

For the plant community, the rate of CO2 production may be affected by:

  • Type and density of plants
  • Temperature
  • Moisture
  • Sunlight
  • Soil chemistry

Carbon flux will vary with the weather, throughout the day, and the year as the season’s change. Measuring CO2 flux provides an excellent jumping-off point for engaging in NGSS practices regarding the earth’s carbon cycle.

Creating a model of the Earth’s carbon cycle
Figure 1. Collect data, and construct explanations. Integrating a range of analytical results can form the basis for creating a model of the earth’s carbon cycle and designing solutions to problems such as climate change and food production.

Students can define their research questions and problems, analyze the results, and generate designs to conduct a variety of controlled experiments using the chamber. Most experiments will identify the CO2 concentration inside the chamber as the dependent variable and will test the effect of an independent variable of students’ choice.

On land, students can compare CO2 flux on soil, lawn, forest, sunny vs. shady areas, and in a wide variety of other situations. In general, when the chamber is on bare soil or leaf litter, the CO2 concentration inside the chamber will be expected to increase, usually within a short period such as 5 or 10 minutes. Figure 1. For longer investigations, the sensor can be placed in logging mode (storing data to internal memory) and left for ~24hrs before the batteries will be depleted.

Logging Mode Video

 

The chamber can be placed over plants that can fit inside it, in which case CO2 concentration inside the chamber should decrease, although it may be counteracted by respiration. The chamber can even be used on water by wrapping a piece of foam insulation around it, allowing it to float.

In any type of environment, students can design their studies to investigate the effect of different variables on CO2 flux.

How to make a Pretzel Barrel CO2 Chamber

The chamber is made of a plastic pretzel container available in supermarkets.

  • Draw a straight line around the container, then cut it in half using a razor knife to form two large plastic chambers open at the bottom and closed on top.
  • You have two options here. You can cut a hole in the top for a CO2 sensor using an electric drill or a razor knife. The hole should allow the CO2 sensor to fit snugly, keeping the container airtight; the hole can be adjusted with tape if necessary to create a tight seal around the sensor. Alternatively, the sensor can be placed inside the container since it’s wireless!
  • The chamber is now ready to be used by placing it on top of soil and measuring CO2 flux.

For aquatic environments, wrap a piece of foam pipe insulation around it.

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