We started class with a quick introduction to the six simple machines: lever, inclined plane, wedge, screw, wheel-and-axle, and pulley. We talked about how all machines make life/work easier and that some need a power source to run while others, such as the simple machines, do not.
We completed the lab "Levers" to show just how one of the simple machines can help make things easier.
For this lab, the students were given a stack of four hardcover textbooks and were asked to try to lift the stack of books with their pinky finger. As you might imagine, they had a tough time with this! They were then given two pencils and instructed how to make a basic lever by placing one pencil on top of the other (in a + shape). The students then placed the pencils so the point of the top one was under the stack of books. They pressed down on the eraser end of the top pencil and saw how this lever was now able to lift the stack.
Levers - Rigid bars that pivot on a fulcrum (fixed point). In that first lab, the bottom pencil served as the fulcrum.
Levers are classified as either first-class, second-class, or third-class. Each class has a different fulcrum and load position. We spent some time discussing each lever and completed a short experiment for each one.
First-Class Levers - In a first-class lever, the fulcrum is located between the effort force and the load. To lift a load, a downward force must be applied to the opposite end of the lever. A seesaw is a good example of a first-class lever.
For this lab, the students were given a small cardboard crate, some marbles, a lever, a fulcrum, and a spring scale. We started out by placing the fulcrum far away from the load position (almost at the opposite end of the lever). The students then placed the crate of marbles (our load) on the end of the lever that was away from the fulcrum and the spring scale on the end near the fulcrum. The students then pulled down on the spring scale until the load began to move. They noted how much force (in ounces) was required to lift the load.
The students then repeated this lab after moving the fulcrum so it was located under the center of the lever. They noticed it took less effort to lift the load when the lever was in this position.
For this lab, we taped the fulcrum to the edge of a desk then set up the lever by placing the fulcrum at one end of the lever bar. Our lever was hanging off the end of the table. We tied a string around the end that was hanging off and hung the marbles (in a drawstring bag) on the lever about 2 inches from the fulcrum. The spring scale was hooked onto the piece of string and the students pulled up on the spring, noting how much force was needed (in ounces) to lift the lever. We tried this again with the load (bag of marbles) 5 inches from the fulcrum and 8 inches from the fulcrum.
Third-Class Levers - In a third-class lever, the effort force is located between the load and the fulcrum. A fishing rod, with the effort force (reel) between the fulcrum (handle) and load (hook) is an example of a third-class lever. Tweezers are another example.
To demonstrate how third-class levers operate, the students taped the fulcrum to the underside of a desk (at the edge) with the point facing down. One student held the lever bar so one end was at the fulcrum. We tied a piece of string to the lever about 2 inches from the fulcrum and added the drawstring bag of marbles to the opposite end of the lever. The spring scale was then attached to the string. The students pulled on the scale and recorded the force needed to lift the load. We then repeated this with the scale placed at a distance of 5 inches from the fulcrum and again at 8 inches from the fulcrum.
Inclined Plane - An inclined plane is a smooth, flat surface tilted at an angle like a ramp. Instead of lifting a load straight up, an inclined plane allows a load to be moved over a longer distance to reach the same height. This requires less effort.
Inclined Plane lab - We used the lever bar from the previous labs to create our inclined plane or ramp for this experiment. The students used books to create an incline, starting with one book. The cardboard crate was filled with 40 coins to create a load. The students placed the load at the bottom of the ramp and used a piece of string to attach the spring scale to the load. They then pulled on the scale and measured the effort needed to pull the load to the top of the ramp. We repeated this lab using 2 and 3 books to create steeper inclines.
Wedge - A wedge is two inclined planes back-to-back. Wedges work by changing the direction and amount of force. Some examples of wedges include an ax, nails, a knife, and teeth!
Wedge lab - For this lab, the students used different materials to attempt to lift a crate of marbles. The students used the eraser end of a pencil, the point of a pencil, a crayon, and the pointy end of a pair of scissors to attempt to lift the crate of marbles. The students discussed which ones made the job easier. The pencil point and the scissors were found to be the best wedges.
Screw - A screw is an inclined plane wrapped around a cone or column.
"Lifter" lab - Each student was given a large wood screw. They placed two fingernails on the first ridge at the tip of the screw and then turned the head of the screw to observe its movement.
Screws are used to connect things but they can also be used to lift items. Screw jacks, for example, can lift houses or cars.
We had just enough time at the end of class to go back and complete some more labs on the simple machines we covered today.
"Ramp" lab - This lab showed how a winding mountain road is an inclined plane.
The students were each given a pencil, a ruler, a piece of paper, and some tape. They cut a 5-inch square from the piece of paper then drew a diagonal line across the square. The students cut across the line and colored the longest edge of one of the paper triangles. They then taped the triangle to the pencil so the shortest leg of their triangle was taped vertically to the pencil. The students then wound the paper onto the pencil and saw the colored line make a shape like a winding road or screw around the pencil.
As we discussed, inclined planes make work easier by gradually traveling upward over a long distance. A winding mountain road is a longer way up a mountain but it is easier than traveling straight up a side of a mountain.
"Weakling" lab - This lab demonstrated a second-class lever.
Each student was given a toothpick. They placed the toothpick across the back of their middle finger at the tip of their fingers and under the first and third fingers. The students then tried to break the toothpick by pressing down with the first and third fingers. We tried this again by moving the toothpick down to the first knuckle of the middle finger.
In this lab, the fingers were acting as a second-class lever similar to a nut-cracker. The fulcrum in this lever is where the fingers join the hand so more force is needed to break the toothpick when it if placed farther from the fulcrum.
The labs "Levers," "Ramp," "Lifter," and "Weakling" are from Physics for Every Kid.
VanCleave, J. (1991). Physics for Every Kid: 101 Easy Experiments in Motion, Heat, Light, Machines, and Sound. San Francisco: Jossey-Bass.
The labs "First-Class Lever," "Second-Class Lever," "Inclined Plane," and "Wedge" are from a Lakeshore Learning Science Activity Tub on Simple Machines.
**We will take two weeks off for Winter Break so there will be no class on December 23rd or 30th. Our last class for the Fall semester will be held on Thursday, January 6th. During that class we will finish up simple machines and see how simple machines can be combined to create compound machines.
Learning Center classes for the Spring 2011 semester will most likely begin during the week of February 21st. Check your e-mail in the new year for information about class offerings.
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