Italicized font represents information to be shared orally or physically completed with the students at this time.

The non-italicized font represents additional information included to support the teacher’s understanding of the content being introduced within the CELL.

ASK WHY

Remind students that as they look about, they probably see half a dozen machines that they don’t recognize as such. Ordinarily, people think of a machine as a complex device-a gasoline engine or a washing machine. They are machines; but so are a hammer, a screwdriver, a bike’s wheel. A machine is any device that helps you to do work.

BRANCH OUT

Remind students that naval architects know that the more weight a boat carries, the lower it sits in the water and the more water resistance it creates. That’s why they design boats with sharp narrow bows. This wedged design allows the boat to push water cleanly out of the way.

GET FOCUSED

GO DEEPER

As a class, read the Background(s) in the Investigation. Have students read the information aloud or silently to themselves. When students have finished, discuss the following concept as a class:

• A pulley is one type of simple machine. It consists of a small wheel with a groove that a rope or string can slide over.
• Pulleys can be fixed to an immovable object or they can be freely floating.
• When pulleys are discussed in scientific terms the mass that is to be lifted is called the load force.
• The length of rope or string that extends from the load to the pulley is called the load distance.
• The force that is applied to the rope or string to lift the load is called the effort force.
• The length of rope or string from the pulley to where the effort is applied is called the effort distance.
• Although work may seem easier if a simple machine is used, machines do not decrease the amount of work done.
• Mechanical advantage describes the relationship between the effort force (force needed to lift the load) and the force of gravity on the load (load force). This can be expressed mathematically by the following equation.       
• Mechanical Advantage = Load Force ÷ Effort Force
• The amount of work done to lift a load may “seem easier” if a machine offers a mechanical advantage greater than 1.

Note: These concepts are integrated into the Background(s) and are used to deepen students’ comprehension of the big ideas.

LEARN THE LabLearner LINGO

The following list includes Key Terms that are introduced in the Investigation Background(s). They should be used, as appropriate, by teachers and students during everyday classroom discourse.

• force
• load force
• load distance
• effort force
• work
• Joule (J)
• mechanical advantage

• Note: Definitions of these terms can be found on the Introduction page to the CELL.

  Note: Additional words may be bolded within the Background(s). These words are not Key Terms and are strictly emphasized for exposure at this time.

SET FOR SUCCESS

• Direct students to complete the Recall section in their SDRs. Student answers may vary.

• What is mechanical advantage?
• Do pulleys change the amount of work done to lift a load?
• Do one and two pulley systems provide the same mechanical advantage?

• As a class, elicit prior knowledge about simple machines. Encourage students to generate examples of types of simple machines they might encounter at home or at school. Student answers may vary.

Note: Simple machines are devices that make work seem easier to perform by changing the distance over which a force is applied to a load and by changing the direction in which the force is applied. Examples students may list include but are not limited to wheelbarrows, crow or pry bars, hammers, see-saws, playground slides, wheels and axles on a car, gears in a mechanical clock, bicycle gears, arms, legs, hips, shoulders, bottle openers, pull tabs on drink cans, wheelchair ramps, inclined driveways or sidewalks, garlic presses, jar lids, bottle caps, screws, doors, doorknobs (lever and round), hole punch, pliers, wrenches, and a block and tackle.

• As a class, encourage students to classify how the machines listed above could be grouped based on their mode of action. Student answers may vary.

Note: Wheelbarrows, crow or pry bars, see-saws, arms, legs, bottle openers, pull tabs, garlic presses, lever doorknobs, doors, the hole punch, pliers, and wrenches are levers. Round doorknobs, wheels and axles on cars, gears in mechanical clocks and bicycles, shoulders, and hips are all examples of wheels and axles. Wheelchair ramps, inclined driveways and sidewalks, screws, bottle caps, and jar lids are inclined planes. A block and tackle is a pulley system.

• Play the video below. Stop to ask students questions or answer students’ questions when necessary. Remind students to follow along with their SDRs and make any notes that they think might be helpful.
• After the video, direct students to divide into their lab groups to discuss their strategy for the lab. For example, they may assign certain group members to perform specific functions during the lab.

Note: The purpose of the video is to allow students to anticipate the laboratory experience they will soon encounter. Students should leave this PreLab session with a firm idea of what to expect and how to perform in the lab.

Note: Homework is posted below the video.

HOMEWORK

Tell students that they should review the Investigation in preparation for the Lab.