- Nail the 6.8cm x 21.0cm x 3.8cm wood piece into the front length of the base board, so it is centered. Use 2" nails and nail from the bottom
- Nail the 10.4cm x 3.8cm x 5.0cm wood block into the center back of the support piece previously added using a 3" nail.
- Nail each wood column to the front support piece, using a 3" nail, so that they lie on each side of the block
- Slip another 10.4cm x 3.8cm x 5.0cm wood piece between the pillars. This swill act as a support piece to keep the two columns straight
- Nail a screw-eye on each side of the pole at 3cm and 18cm from the top
- Tie three elastics (5.0cm in diameter each) to each of the top pair of screw-eyes
- Attach the thin cylindrical wood piece to the remaining piece of wood (29.0cm x 8.0cm) by stapling it with U-type nails 5cm from one of its ends
- On the other end, lightly hammer in two 1" nails 0.75cm from each side of the center, 2.0cm from the edge. These will act as a placeholder for the spherical projectile
- Lightly hammer in two 1" nails to the sides of the wood piece so they are 7cm from the other side. Make sure most of the nail is sticking out as the elastic bands will be hooked onto here
- Slip the ends of the cylindrical wood piece through the screw-eyes on the bottom and wrap a small elastic band around each end as a stopper
- Slip the ends of the bundle of elastics onto the nails sticking out from the sides of the attached wood piece
- To finalize, put the remaining elastic band over top of the two pillars so it rests on top, above the screw-eyes.
Figure 4.1: Finalized projectile launcher
Using the Projectile Launcher and Collecting Data
- Pick a flat, even surface that has nothing that would potentially interfere with the path of the projectile
- Place the projectile launcher on the ground so that there is around 10 meters of open space for the projectile's path
- Place the ball (projectile) between the two nails sticking out of the rotating arm
- Put weight on the base board, for example by stepping on it or getting someone to step on it, so it does not lift up from the force applied to the arm
- Apply force to the arm, pulling it back until it is at 90 degrees to the vertical (completely horizontal). You may need to lightly keep the spherical ball in place as it may begin to roll backwards
- Let go of the arm. The arm will thrust upwards, putting the projectile in motion
- Mark where the projectile lands. The distance it rolls after landing does not count in its distance traveled
- Measure the distance from the projectile launcher to the landing spot and record the data
- Repeat steps 3-8 twice, each time with a "different" ball (same ball with same measurements and maybe some negligible differences)
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Further Changes to the Structural Design and Procedure
Problem
After sketching a final structural drawing and designing a procedure for the building and testing the projectile launcher, modifications were made to increase the efficiency of the design.
The flaw to the structural design/procedure was the two 1" nails that were used as a holder for the projectile as rotating arm was retracted While this method was effective in keeping the projectile in place with minimal manual support (i.e. lightly supporting it with your hand), it was found to interfere with the motion of the projectile, specifically its release. It was observed that with this design, the projectile would travel extremely minimal distances, despite the force behind the launcher, and on one occasion case have a backward displacement. This is due to the two nails providing a backwards force against the direction of motion of the projectile.
As the arm begins to rotate from a position horizontal to the ground to the starting position of 20 degrees, the projectile begins to leave its resting position. While theoretically the ball leaves rest at an angle perpendicular to the surface it lies on, meaning that the nails nailed straight into the wood should have little contact against the ball, experimentally, they push against the projectile, pushing the projectile upwards. On top of that, friction may play a role and the heads of the nails may even exert a downward force onto the projectile, forcing it into its resting position.
As the arm begins to rotate from a position horizontal to the ground to the starting position of 20 degrees, the projectile begins to leave its resting position. While theoretically the ball leaves rest at an angle perpendicular to the surface it lies on, meaning that the nails nailed straight into the wood should have little contact against the ball, experimentally, they push against the projectile, pushing the projectile upwards. On top of that, friction may play a role and the heads of the nails may even exert a downward force onto the projectile, forcing it into its resting position.
Modification
The solution to the problem would be a feature that would be able to keep in-place the projectile without interfering with its flight. The two nails were uniquely replaced by part of a contact lens package that has a spherical shape to it. With a diameter just under that of the projectile, the projectile is able to firmly sit on it without any parts coming in major contact with it at the sides; the ball is kept in place from the bottom and not the sides this time.
Added to the materials list would be
- Cut out contact lens package (approx. 2.0cm - 2.5cm in diameter)
- Hot glue gun
Step 8. of building the projectile launcher would be replaced with placing the contact lens package piece, at the same position 2.0cm from the edge in the center of the rotating piece.
Figure 4.2: Modification to the structural design
