Week 7

learning intentions

• explore the mechanics of pulleys and investigate their practical applications in force transfer within mechanical systems

Tasks

Knowledge & understanding

1.  Pulley Worksheet on Google Classrooms

 Investigation Skills

2. Pulleys

Literacy & research

3.  Game

Equation of the mechanical advantage  of a machine based on the number of ropes or cables supporting the load.

There is another way to determine mechanical advantage though. We can measure it directly by measuring the decrease in force used to lift an object. Let's refer to this as the actual mechanical advantage.

The mechanical advantage of pulleys has been used by engineers for thousands of years. Archimedes (b. 287 BC, d. 212 BC) was a Greek thinker and engineer. When Rome was attacking Syracuse (where Archimedes lived), he devised a pulley attached to a great lever that extended over a rock wall and dangled a giant hook. When Roman ships approached, the hook was lowered, grabbing the ships. The pulley then lifted the huge ships out of the water, only to drop them back down with a devastating crash. Since then, countless engineers have used pulleys to lift heavy objects for a variety of different purposes. Pulleys designed by engineers can be found on assembly lines, construction sites and other places where heavy objects need to be moved.

We have now learned how to calculate mechanical advantage for pulleys. Today, we are going to work on an engineering scenario that has actually happened in years past. For our activity today, imagine that Marine biologists at an aquarium in California have been working to save a sick gray whale that was found off the coast of Big Sur. The gray whale has been in their care for several months and is now completely healthy. We work at the engineering firm that they have hired to design a lift that will safely remove the whale from the aquarium and move it back into its natural environment. We will need to design a system that can lift the 16 ton (32,000 pound) whale to a certain height in order to be moved back into coastal waters.

As engineers, we know that there are several steps that need to be completed in the design of a solution for any technical problem. The first step in designing a proper solution is to recognize the need. Who is the customer that we need to make happy? In this case, it is the aquarium, the whale, and perhaps the citizens who have been keeping track of the whale's story in the news.

The next step is defining the problem needs. What is one way that we could phrase this problem with moving the whale? (Discuss with the class. Answers should not limit the solutions, so one idea may be: get the whale back to the ocean safely.) Next, an engineer would think about information that might help to solve the problem. Needed information might include the constraints or limitations on the problem, such as money or time the whale can be out of the water, but we would also consider what we need to know to solve the problem.

Today, we are going to look at various pulleys as a way to lift the whale out of the tank in the aquarium. We will be setting up different pulley systems and examining if the theoretical mechanical advantage is the same as the actual. We are going to test the calculations we make for the mechanical advantage of the pulleys. We will learn if these calculations actually predict what happens in the real world. After we learn about pulleys and their mechanical advantage, we will brainstorm ideas for the whale lift to present to the aquarium.