# Build

## Instructions

• 1

Here are some of the materials you can use

• chipboard cardboard, such as a cereal box (8 ½ x 11 in. [22 x  28 cm])
• container partially filled with water, such as a wide plastic bin
• duct tape
• 2 paper cups (8 oz. [237 ml] or larger)
• plastic wrap
• 5 rubber bands
• scissors
• 4 straws
• towels (paper or cloth)
• washers (1-in. [2.5 mm] or larger)
• 4 wooden skewers or dowels
• 2

• Have paper and a pencil ready to write down ideas and sketches as you design.
• Put newspapers on the floor. Place the bin in the middle. Fill it with water.
• Get a pile of towels to have on hand in case of spills.
• Think about boats you have been in or seen on the water. How did they move across the water?
• 3

• How does a boat keep from sinking in the water?
• How will you keep your boat from tipping or rolling over?
• How many paddles does a boat need in order to move?
• TIP: The force, or pressure, that pushes back on an object (the boat) in the water is called buoyancy. When a boat (or any object) is placed in the water, it causes the water to push upward against it with a force that’s equal to the weight of the water it moved (or displaced).
• TIP: A boat can get tippy when one part is heavier than another.
• TIP: Explore how a paddle moves. Looping a rubber band over your thumb and index finger, then slide a piece of chipboard through the rubber band and wind it up. Let go so the chipboard spins around.
• 4

• What source of energy will you use to power your paddles?
• How can you develop the force you need to move your boat through the water?
• How big does your paddle need to be to reach the water and drive the boat?
• TIP: When you stretch a rubber band, it gives the rubber band potential energy—which is stored energy. When you let go of the rubber band, it transforms the potential (stored) energy into kinetic energy—or motion energy.
• TIP: Inventors’ and engineers’ first ideas rarely solve a problem. They brainstorm ideas, try different ideas, learn from mistakes, and try again––this is part of the design process.
• 5

Look at the materials

• What materials do you have to build a boat?
• What materials will you use to build a paddle frame?
• How will you power the boat so it moves in the water?
• 6

Design and build the boat

• Decide what materials you will use to build your boat.
• Think about materials that will keep your boat from sinking or tipping over.
• Choose your materials and build the boat.
• TIP: If you add some weight to the bottom of your boat, you can help keep it upright.
• TIP: To keep your boat from sinking, make sure all openings are sealed tight.
• 7

Design and build the paddle frame

• Choose the materials and build the paddle frame.
• Attach it to the boat.
• TIP: If you want the paddles to rotate together, try including an axle on the paddle frame. An axle is a rod passing through the center of each paddle.
• TIP: If the paddle frame goes through the boat, be sure to seal the entry holes so water doesn’t seep inside.
• TIP: If the paddle frame has parts that bend when the rubber band is wound tight, try moving the rubber band closer to the boat. This will make it harder for the frame to bend. Or, find ways to add support to any parts that bend.
• 8

Attach the power source

• Chose the rubber band you want to use to power your boat.
• Attach the rubber band to the paddle frame and the boat.
• TIP: Different lengths and widths of rubber bands will wind around the axle differently, store different amounts of energy, and release their energy differently.
• 9

• Decide how many paddles you need to make your boat move in the water.
• Test the paddles to see that they rotate freely.
• TIP: If the paddle frame bends from the weight of the paddles, try reinforcing the frame with a wooden skewer or other less flexible material.
• TIP: If your paddles hit the paddle frame, try moving the rubber band. Or consider changing the size of the frame or paddle.
• 10

Check and seal all openings

• Look for any openings where water can get into the boat.
• Choose materials that will keep water from getting into the boat.
• Seal the openings and waterproof your boat.
• TIP: Water can leak into small, open areas; check any places that you cut open or where you poked an opening in the boat.
• TIP: You’ve just built a prototype, which is an early version of a product. Prototypes help engineers understand a product’s strengths and weaknesses and how the product might be improved.
• 11

Watch it go

• Wind up your rubber band.
• Place the boat in the water.
• Release it and watch it paddle across the water!
• TIP: If the boat doesn’t move across the water, try winding up the rubber band more. The more stored energy you have in the rubber band, the more energy will go into powering the paddles—and the faster and farther the boat will go.
• TIP: If the paddle warps when it gets wet, try protecting it by wrapping it in something waterproof.
• TIP: If the boat tips and does not let the paddle hit the water properly, add weight to the boat to control its position. Tape a few pennies to the bottom of the boat. Weight that is used to keep a boat upright is called ballast
• 12

Did you know?

• Pedaling Through the Sky
Engineer Paul MacCready was always intrigued by the way birds soared through the sky. As an adult, he brought his passion to life by building gliders and other aircraft.

In one of MacCready’s planes, the Gossamer Condor, the pilot pedaled a special bike that could spin the bike’s propeller. The Gossamer Condor had a wingspan of 96 feet (20 m)! It was 30 feet (9 m) long and 18 feet (5.5 m) high—bigger than a tractor-trailer truck. But it weighed only 70 pounds (32 kg)—which was less than half the weight of the pilot!
• 13

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