1. Introduce the concept that simple machines make work easier.

Tell the class the definition of work used in science may differ from what most people think of as work. Work can be defined as force times distance (Work = Force x Distance). Ask a student to move a book from one desk to another. Ask: Is this work by the scientific definition? (Yes, this is work.) You are applying force for a certain distance. Ask: Is doing homework work by this definition? (No, homework is not work.) Pushing a book across a desk is work because you are applying a force (a push) on a book for a certain distance (the length of the desk). You are not pushing homework anywhere.

Imagine that you want the same amount of work to get done using less force. In this example, this means you still want the book to move from one side of the desk to the other, but you don’t want to push as hard. If you use half as much force to push the book, then you will have to push the book twice as far to do the same amount of work. Or, you could use a simple machine to make up the difference in the force you are applying. Explain that people often use simple machines to make work easier.

Introduce the class to the names of various simple machines and show them a picture of each from the Simple Machines photo gallery: levers, the wheel and axle, pulleys, screws, and inclined planes. Tell the class simple machines make work easier by increasing mechanical advantage. Tell students that an example of mechanical advantage is using the claw of a hammer to remove a nail. A small force applied to the handle of the hammer produces a greater force at the claw end of the hammer, allowing for the removal of stubborn nails.

Explain that complicated machines, such as robots and cars, are made up of combinations of simple machines and other parts. Robots are complex machines that contain many simple machines. Some examples of simple machines that are used in robot construction are wheels and axles for mobility, allowing robots to move from place to place, and robot arms, which are levers, enable them to manipulate objects.

Explain that students are going to try simple experiments with simple machines, and then use those simple machines to solve challenges.

2. Demonstrate how levers work.

Construct a lever by taping a marker parallel to the edge of the table. Tear off a piece of masking tape, loop it, and attach it to the end of the ruler. Place the ruler on the marker at the center point, like a seesaw, and then press a tennis ball firmly to the tape. Invite a student volunteer to demonstrate the lever; first, have the student gently lift the ball by applying force to the end of the lever (ruler) opposite the ball. Second, instruct the student to reposition the lever (ruler) so the ball is as close to the fulcrum (marker) as possible. Have the student press the lever again to lift the ball. Lastly, reposition the lever (ruler) so the ball is as far away from the fulcrum (marker) as possible while still leaving a portion of the lever (ruler) to be pressed down. Have the student press the lever to lift the ball again. A photo of each lever situation is available in the Simple Machines Demonstrations photo gallery.

Discuss what the class saw and what the volunteer observed. Ask: Which lever configuration made the ball easiest to lift? Which lever configuration made it the most difficult to lift the ball? Which lever configuration moved the ball the farthest from its starting position? How does the lever provide a mechanical advantage when moving the ball?

3. Students complete a challenge using levers.

Introduce the lever challenge. Explain that each group will attempt to move a tennis ball from the table to the center of a roll of masking tape at varying distances. Introduce the rules. Hands may not be used to move the ball to the goal, but hands may be used to place the ball on the lever and to operate the lever. Nothing may be used to secure the ball to the lever. The marker may not be moved from the edge of the table. The masking tape roll may not be moved unless the teacher instructs it. The winner will be the group that moves the ball to the center of the masking tape roll from three different distances with the least amount of attempts.

Separate the class into groups of 2-4. Distribute the following items to each group: a tennis ball, a rigid ruler, a cylindrical marker, and a roll of masking tape. Instruct students to tape the marker parallel to the edge of a desk or table, as was demonstrated earlier by the teacher. Now, instruct groups to measure 24 cm (9.5 in) out from the marker and place the edge of the masking tape roll, flat on its side, at this point.

Allow groups a few minutes to collaborate on different ideas for getting the ball into the goal. Next, allow five minutes of exploration and experimentation. Instruct students to record the distance of 24 cm (9.5 in) in their journal and sketch the lever configuration that worked best at this distance directly beneath the number. Follow the same steps at a distance of 15 cm (6 in) and 5 cm (2 in). Lastly, the teacher will observe as groups demonstrate their lever configurations at the different distances. The group with the lowest total attempts after completing all three distances wins.

4. Students are introduced to the pulley using a demonstration.

Tell the class that pulleys make work easier by reducing the effort needed to lift an object. Instruct a student to lift a milk jug filled with water using only his or her hand. Next, have two additional students hold a broom handle at shoulder level between them. Now, tie a thin rope to the handle of the jug and let it rest on the floor. Instruct the student who earlier lifted the jug to pull the rope over the broomstick and pull down on the end of the rope to lift the jug. Ask the student to describe the difference between the two experiences. Now, untie the rope from the jug and tie one end of the rope to the broomstick. Have the two students continue to hold the broomstick at shoulder level while the other volunteer slips the free end of the rope through the handle of the jug and then back over the broomstick. Have the same student pull the end of the rope to lift the jug. Ask the student to describe the differences in the three experiences. A photo of the second and third situations are available in the Simple Machines Demonstrations photo gallery.

5. Students complete a challenge using pulleys.

Introduce the pulley challenge. Each group will lift metal objects from the floor using a pulley system they design. Introduce the rules. Only materials provided may be used in the design. Hands may not be used to pick up objects.  An object lifted to at least 10 cm (4 in) in the air may be removed from the pulley using the hands. At least two spools must be incorporated into the design. No more than 15 cm (6 in) of tape may be used. Part of the pulley system may be taped to a fixed object, such as a desk.

Separate the class into groups of 2-4. Distribute the following items to each group: three plastic spools; a meter (3.2 ft) of string; a 1¼-inch donut magnet; various small metal objects, such as paper clips; masking tape; and three pencils. Allow groups time to collaborate on different ideas for pulley construction. Next, allow five to ten minutes of exploration and experimentation with the materials. Encourage students to make sketches of ideas in their journal.  At the conclusion, each group will demonstrate for the teacher the most successful pulley system the group designed.

6. Students are introduced to the wheel and axle.

Tell students the wheel and axle uses rotational movement to make work easier. When effort is applied to the wheel, it produces movement in the axle, and when it is applied to the axle, it produces movement in the wheel. Ask a student to hold the narrow end of a funnel and use it to roll the large end of the funnel along the table. Ask: Is this an example of effort being applied to the axle or the wheel? (Effort applied to the axle.) Next, have a student tape the end of a 1 m (3.2 ft) piece of string to the narrow end of the funnel. Now have the student turn the funnel in a circular motion using the large end of the funnel. Ask: Is this an example of effort being applied to the axle or wheel? (Effort applied to the wheel.)

7. Students apply knowledge of the wheel and axle to complete a challenge.

Introduce the wheel and axle challenge. Each group will attempt to move a tennis ball 3 meters (roughly 10 ft) using a design incorporating the wheel and axle. Introduce the rules. Only materials provided may be used. The ball may not be touched after it begins to move. The wheel and axle must be the primary mechanism by which movement of the ball is achieved.

Separate the class into groups of 2-4. Distribute the following items to each group: two pieces of cardstock paper, approximately 57 g (2 oz) of modeling clay, two drinking straws, 30 cm (12 in) of masking tape, and 30 cm (12 in) of string. Allow groups time to collaborate on different ideas for moving the ball. Next, allow ten minutes of exploration and experimentation. Encourage students to make sketches of ideas in their journals. When all groups are ready, they will compete to determine which design can move the ball the greatest distance. Give groups five minutes to reengineer or repair their vehicles after the first test, and test a second time.

8. Students use simple machines to design a robot on paper.

Ask the class to imagine how the simple machines they experimented with could be used to construct various working parts of a robot. Ask the following questions: How could a lever be used? (Perhaps as part of the arm or leg.) How about a pulley? (It could be used to operate the gripper on a robot’s arm.) What about the wheel and axle? (It could be used as part of the mobility unit.) Instruct students to create drawings of their own robots incorporating all of the simple machines they experimented with in class.