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AREAS OF SCIENCE

Physics

METHOD
 Engineering Design Process


Ski lifts make use of a type of simple machine called a pulley. A pulley is a wheel with a rope wrapped around it. Sometimes pulleys are used to help lift heavy objects vertically off the ground. Other times pulleys are used to transport things horizontally over long distances or across rough terrain (see Figure 2, below). They can also be used to move objects diagonally (a combination of horizontal and vertical movement) like with a ski lift. A pulley typically uses a wheel because it helps reduce friction, or the force that opposes motion between two surfaces that are sliding against each other. Friction can also generate heat and cause materials to wear down quickly.

ski-lift
Figure 1. Ski lifts make it much easier for skiers to get to the top of a mountain. Imagine having to walk all the way up instead!

Design and build your own model ski lift to transport an object from a start area to a finish area.

  • Ski lift
  • Simple machine
  • Pulley
  • Friction
  • Model
  • Design requirements
  • Iteration
  • What is a ski lift and for what are ski lifts used?
  • What is a pulley and for what are they used?
  • What is friction? What does a pulley use to help reduce friction?
  • What are other types of simple machines?
pulley-vertical-horizontal
Figure 2. Pulleys can be used for different purposes. (Left) If you pull on the rope (blue arrow), the weight will lift up off the ground (black arrow). (Right) If you spin the pulleys (blue arrows), the weight will move horizontally (black arrow). A ski lift is more similar to the setup on the right, but it usually travels up a hill instead of over flat ground.

In this project, you will design and build a miniature model ski lift from ordinary materials you already have around your home. A model is a smaller version of something scientists and engineers build for testing purposes. For example, engineers build smaller models of cars, airplanes, and bridges to help them with their designs. Your goal will be to transport a cargo item from one point to another; however, Science Buddies will not provide an exact template or instructions to build your ski lift. This is an engineering design project, which means can think creatively about how to solve the problem, then design, test, and improve your own solution.

The list of materials below is just a suggestion to help get you started with the project. Since this is an open-ended engineering design project, you can use any other materials you can think of.

  • Plastic cups
  • Pencils or popsicle sticks
  • String
  • Paper clips
  • Binder clips
  • Paper or cardboard
  • Small, shallow cardboard box or bowl
  • Items to use as "cargo," separate from your construction supplies, such as coins, individual paper clips, binder clips, etc.
  • Masking tape
  • Ruler
  • Scissors
  • Optional: Smartphone or digital camera to take pictures of your design
  • Lab notebook

The goal of this project is to build a model ski lift device that can transport a small cargo item horizontally from a start area to a finish area (many real ski lift also go vertically up the side of a mountain, but you will start out with a flat surface). The catch is that the human operator can only touch the device in the start area. This makes a pulley system very useful for transporting the items horizontally.

Since this is an engineering project, you need to specify your design requirements. Here are the basic requirements for the project, but you can add your own requirements if you want:

  • The device must safely transport an item from the start area to a box in the finish area a certain distance away.
  • The operator can only load, touch, and handle the device from the start area.
  • The cargo item cannot fall out of the device or touch the ground before it reaches the box in the finish area.
The following sections in the Procedure will walk you through how you can design, build, and test your model ski lift.

Once you have defined your design requirements, you need to start designing your ski lift. The design phase is an important part of the engineering design process. There is no fixed procedure for this section; you get to come up with your own design! If you are new to the engineering design process, here are some suggested steps to get you started:

  1. Re-watch the video above and look closely at how the example device operates.
  2. Think about how you could build a simplified "pulley" system using string. While real-world pulley systems use wheels to help reduce friction, in this project it might be okay if you just have string sliding over a smooth, round surface, like a pencil or paper clip. The example video above shows string looped around two paper clips.
  3. Think about how you will be able to operate the device while only touching it on one end. Will you be able to pull on the string in one place, causing the entire pulley system to move?
  4. Think about how you can automatically drop the cargo item into the box in the finish area. Remember, you are not allowed to touch any part of your ski lift, or your cargo item, outside of the start area. The example video above shows a "chair" that is designed to tip sideways when it bumps into the box, causing the item to fall out and land in the box.
  5. Make a sketch of your design on paper before you start building. Make a list of the materials you will need to use, and label the different parts on your sketch. Figure 3, below, shows an example sketch.
ski-lift-sketch

Figure 3. An example sketch for a ski lift design.

Figures 4–7, below, show some close-up pictures of the ski lift from the example video. You can use these pictures as inspiration for your design, but remember, you should come up with your own original design!

ski-lift-office-supplies

Figure 4. For the example model ski lift shown in the video above, the entire setup looks like this. The ski lift is designed to transport a small object from the start area (on the right) to the box in the finish area (on the left).

ski-lift-supports

Figure 5. The supports at either end of the ski lift are made from plastic cups, wooden pencils, and tape. The plastic cups are taped to the tabletop so they do not fall over.

ski-lift-paper-clips

Figure 6. The string is wrapped around a paper clip at either end to form a simple pulley system. Even though the pulleys do not actually have wheels, the paper clips are very smooth, so the string can slide over them with very little friction.

ski-lift-chair
Figure 7. The "chair" that carries the cargo item (a mini binder clip) is designed so that when it bumps into the box at the end, it tips over and spills the cargo out.

Building Your Ski Lift

Once you are done designing your ski lift, it is time to start building! Again, there is no fixed procedure for this section. How you build your ski lift will depend on the design you came up with and the materials you decided to use. Once you think your ski lift is ready, move on to the next section to begin testing.

Optional: If you have a digital camera or smartphone, take pictures of your ski lift. This will help you document your design process, which will be useful when you make your project display board.

Testing Your Ski Lift

Now it is time to test your ski lift, and possibly redesign it or make improvements, depending on how well it worked. Engineering projects rarely work perfectly on the first try! The process of redesigning and improving an engineering project is called iteration, which is an important part of the engineering design process. Here is a suggested procedure for testing your ski lift:

  1. Load your cargo item into your ski lift's "chair." Make sure you only handle the ski lift and cargo item inside the start area for your design. Do not touch parts that are outside of the start area.
  2. Operate your ski lift to transport the device toward the finish area. Pay close attention to how the device operates:
    1. Do any parts of the pulley system or supporting structures seem weak or wobbly? Do any pieces fall off?
    2. Does your cargo stay safely in the chair as it is being transported, or does it fall out?
    3. Does your automatic unloading device work as intended? Does the cargo fall into the box into the finish area? Does it miss the box? Does it remain stuck in the chair entirely?
  3. Repeat step 2 a few times until you are comfortable operating your ski lift. Do you see some of the same problems occur with each test? Do the results change if you are more careful operating the device?
  4. Depending on what problems you encounter while testing your ski lift, your next steps may vary. Write down your observations and ideas in your lab notebook. For example:
    1. If your support structures are too weak, how can you make them stronger?
    2. If your pulley system gets stuck, how can you make it operate more smoothly?
    3. If your chair does not successfully unload the cargo into the box, how can you modify its design?
  5. Based on your observations and ideas from step 4, make changes to the design and construction of your ski lift. You may need to add materials, or completely redo part or all of your ski lift, depending on how well it works. Remember that this is alright! There is no "right" answer to an engineering design project.
    1. Optional: If you have a digital camera or smartphone, take pictures of your modifications and a video of your ski lift when it is in operation. This will help you document the different iterations of your design process.
  6. Repeat steps 1–5 as many times as necessary, until your ski lift meets all of your design requirements. Now, think about the design process you went through:
    1. How many iterations did it take before you reached your final solution?
    2. Did you have to make major changes or do a total redesign of your ski lift, or did you only make small changes and fixes?
    3. If you took pictures, compare the first picture of your ski lift to the last picture. How much did your ski lift change?
  7. Optional: Quantify your ski lift's performance. For example, use a stopwatch to time how long it takes you to transport one cargo item from start to finish. Or, see how many items you can transport in one minute.