The Research Experience for Teachers Program http://www.cs.appstate.edu/retActivity Title: Littlebits Throwing Arm and Kinematic Equations

Summary: Little Bits are small, interactive pieces that fit and work together to create electronic inventions. By creating a throwing arm, we can provide a reproducible scenario in order to calculate the velocity and trajectory of the projectile.

Introduction/Motivation: Creating the Littlebits Throwing Arm is a simple, but interesting task, and will allow students to practice their kinematic equations in a real-world scenario. First, we’ll introduce Littlebits, and then create the Throwing Arm. Following this, practice the kinematic equations with some problems, and then we’ll use the Throwing Arm to put your skills to the test. Finally, think about what you could change with the Throwing Arm to make it launch its projectile farther, and then experiment!

Pre-Requisite Knowledge: Kinematic Equations knowledge would be helpful.

Materials List:

a1 Battery & Cable p1 Power i3 button o11 servo & servo hub a23 mechanical arm screws (x3) a9 Mounting Board a24 servo hub wheel o25 Motor

All of the above are included in your Student STEAM Kit. The below, however, are not provided in the kit, but should be provided by your teacher.

Philips Head Screwdriver Scissors Rubber Band Paper Cups Masking tape

For the calculations, you’ll need this:

Pencil & paper Stopwatch Ruler (Optional) Calculator

Procedure:

To begin, let’s create the Throwing Arm. This should not take long: no longer than 15-20 minutes.

Preparation:

Make sure you have all the necessary parts for this project before you begin. Study the picture below to have an idea of what the Throwing Arm should look like.

Assembling the Throwing Arm:

1. Connect the power module to the button module, and finally the servo motor to the other end of the button, as shown below. (Make sure the servo motor switch is set to TURN)

2. To the servo motor, attach the a24 servo hub (the white plastic piece). It should snap into the servo motor. Once this is complete, insert a screw into one of the available screw holes. Only one is needed.

3. Attach the Littlebits Wheel to the servo motor, and then attach the arm itself to the wheel using two screws. Your creation should look something like this:

The screws have not been screwed entirely in, in order for you to see where they go. 4. Cut your cup into the shape below, and then attach it to the other end of the throwing arm using

masking tape.

5. Attach what you’ve made so far to the Littlebits Mounting Board, similar to the picture at the top. 6. Attach the wheel to the other end of the Mounting Board, so that the entire contraption can stand on its

own. You DO NOT plug the wheel into the rest of the Littlebits circuit.

And that’s all for creating the Throwing Arm! For projectiles, crumple up some notebook paper, or use other objects you can find: nothing too heavy, though, or you might damage the servo motor. Whatever you use, make sure you can consistently use and reuse it, in order to get consistent measurements!

Test out your throwing arm a couple times. Make sure it launches in a way that creates a nice, steady, arc, with plenty of airtime, in order for you to accurately measure it. Now, get out your calculator and pencil/paper, and

let’s practice some kinematic equations:

1) Determine the range of a ball (horizontal distance traveled) when launched with a speed of 38.0 m/s at angles of (a) 40.0 degrees, (b) 45.0 degrees, and (c) 50.0 degrees from ground level. Show your work.

2) Referring to the previous question, determine the max heights for each of the three angles.

3) A long jumper leaps with an initial velocity of 9.1 m/s at an angle of 37° to the horizontal. Fill in the blanks below using this information.

vox = m/s voy = m/s tup = s ttotal = sdx = m dy @ peak = m

4) A ball is projected horizontally from the top of a 92.0-meter high cliff with an initial speed of 19.8 m/s. Determine: (a) the horizontal displacement, and (b) the final speed the instant prior to hitting the ground.

5) Determine the launch speed of a horizontally launched projectile that lands 26.3 meters from the base of a 19.3-meter high cliff.

And that should be plenty of practice! Now, let’s see if we can calculate the specifics of the projectile from our Throwing Arm. Place your Throwing Arm on a flat, stable surface (probably the floor) and load, aim, and fire your projectile. Make sure to set it up in such a way where you have plenty of time to measure how long it is in the air.

Have one group member control the stopwatch: their job is to measure how long it takes from when the projectile leaves the Thrower from when it first strikes the ground.

Have another member watch and mark the place where it strikes the ground the first time (before it rolls/bounces)

With these measurements, it is possible to calculate the following:

Initial Velocity:Maximum Height:Final Vertical Velocity:Horizontal Velocity:

And many other specifics about the projectile motion as well. Feel free to take multiple measurements: science is built on repetition.

And that’s all for the math! For the remainder of the time, try and see how far you can launch your projectile. Be creative! Use other Littlebits or other project components to modify your Throwing Arm: for example, a longer arm might help…