# Science and Technology Tasks Week 7

Design and build something that can carry an object from the top of a zip line string to the bottom in four seconds (or less!).

BRAINSTORM & DESIGN

Look at your materials and think about the questions below. Then sketch your ideas on a piece of paper or in your design notebook.

1. Using these materials, what can you design that can carry an object down a zip line?
2.  How will your carrier stay on the zip line as it goes from the top to the bottom?
3.  What kinds of materials should be in contact with the zip line so that the carrier slides quickly?

MATERIALS

• chipboard (from a cereal box or back of a notepad)

• 2–4 small paper cups (i.e., 3-ounce)

• Ping-Pong ball/other object to be transported

• 4 plastic straws

• scissors

• single-hole hole punch

• 4 feet of smooth line (e.g., fishing line or unwaxed dental floss)

• 4 wooden skewers

BUILD, TEST, EVALUATE & REDESIGN

Use the materials to build your carrier. Then make a zip line. Perhaps run the line between the back of a chair and a stack of books. Make sure the high end is about two feet above the low end. Test the carrier by putting it on the line. When you test, your design may not work as planned. The design process is all about “if at first you don’t succeed, then try, try again.”

For example, if your Ping-Pong ball carrier:

• keeps dropping the object—Check that it has a big enough place to hold the object.

• stops partway down—Make sure there’s nothing blocking your carrier where it touches the line.

• doesn’t balance well—Adjust the weights. Add weights or move them so they are farther below the zip line. Doing this changes the carrier’s center of gravity, the point within an object where all parts are in balance with one another. See how changing the numbers and positions of washers affects the carrier’s balance.

• takes longer than four seconds to travel the zip line—Find ways to reduce friction. Yes, there’s friction—the force that resists motion—even when you’re dealing with something as smooth as fishing line. You’ll find friction anytime things rub together. Experiment with different materials to see if you can reduce friction and speed up the Ping-Pong ball carrier.

TAKE IT TO THE NEXT LEVEL

• Slow down! Build a carrier that takes ten seconds to travel the length of the zip line.

• Piggyback time. Make a carrier that can hold several objects at the same time.

• Blast off! Find a way to launch the Ping-Pong ball when the carrier gets to the end of the zip line.

• On your marks. Get set. Go! Set up two zip lines and race different ball carriers.

You have a really heavy load to shift but you have discovered a wheel! (just the one wheel).

Can you use it to devise some form of vehicle to move the load? Model and test your design using the materials provided.

Do wheels make it easier to move things? Why is this?

Do you know of any one-wheeled vehicles?

Here are some ideas to get you started:

1. What are the basic parts that your vehicle will need?

2. How will you attach the wheel to the vehicle so that the wheel can still turn?

3. Draw a plan of how your vehicle will look and so that you can identify what pieces of equipment you will need.

4. Construct your vehicle, test and then modify if necessary.

Here are some extra things that you can do:

1. Have a competition to see whose one-wheeled vehicle can carry the heaviest load.

2. What size of wheel is best? How could you test this?

Talk with the children about wheeled vehicles. Do they know of any with just one wheel? (The wheelbarrow is one with which they should all be familiar.)

Some children may never closely have looked at how a wheel works. The wheel needs an axle (or spindle) to ensure that it turns. There are two approaches to wheel and axle: a) the axle can either be fixed to the frame and the wheel spins freely on the axle (in which case the hole in the centre of the wheel should be large enough to allow the wheel to spin freely) or b) the axle spins free of the frame but the wheel is fixed to the axle (the hole in the middle of the wheel should be small enough to ensure a snug fit to the axle). In this case some mechanism is needed to attach the axle/wheel to the frame using for example a drinking straw - the axle and fixed wheel spin together inside the straw, the straw is fixed to the frame.

Aside from the wheel & axle the children are going to need some sort of frame for their vehicle. The frame incorporates the wheel and axle and carries the load and could have built in handles to push it along. All the parts need to be fixed together – elastic bands, blu-tak and string are good for temporary solutions, tape and glue provide a more permanent solution.

The ‘heavy load’ needs to be decided upon, nothing too heavy (at least initially), this could be anything from a bag of marbles to a packet of lentils and should be the same for everyone.

Background

A wheel makes it easier to move loads because it reduces the friction encountered between the moving surfaces. The wheelbarrow in fact combines the advantages of both a wheel and a lever. The load is centered just behind the wheel and that way, you have to lift only a small part of the load. If the load is placed too far back in the wheelbarrow it becomes far more difficult to move – interfering with the leverage.

Suggested materials

 Assorted wheels (budget option - cotton reels, cardboard wheels cut from cereal packet)

 Wood dowel/plant sticks (of suitable diameter to either fit loosely inside the center hole of the wheel for fixed axles, or snugly into the hole for free spinning axles)

 Drinking straws

 Lollipop sticks/craft sticks

 String

 Assorted plastic cartons, foam trays, yoghurt pots etc.

 For ‘fixing’ – selection of: blu-tak, elastic bands, tape, glue

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