This brings us to the basics of physics. I am going to take this opportunity to water-down the scientific principles of physics to make it accessible. First, students and teachers need to have a common vocabulary concerning the
scientific method, linear measurements, friction
and
inertia
. Next, simple machines
(the inclined plane, the lever, the wheel and axle, and the pulley
) are discussed. These are the basic things students and teachers will need to know about in order to move on to the projects.
The
scientific method
never wavers. A hypothesis is developed; the experiment is planned and run carefully to collect information; measurements are taken thoroughly and recorded properly; and, the hypothesis is checked for support (Goodwin, 18). The question asked is, "Does the evidence collected support the hypothesis?" If yes, success. If no, the method is followed again where another hypothesis is developed.
Careful
measurements
need to be taken so that the experiment may be duplicated by others. Many of the projects require linear measurements. The most common type of linear measurer is the 12 inch ruler. The ruler, as other measurers, uses both the English and metric system. The English system is generally used in the United States, whereas the metric system is most commonly used in other countries. "Scientists all over the world, even those living in the United States, prefer the metric system" (Friedhoffer, 22) because it is easier to convert. This system uses grams, meters, liters, and the Celsius scale. The English system uses pounds, inches, yards, miles, and the Fahrenheit scale. It is a bit more awkward when it comes to conversions. That is why a good calculator is sometimes warranted. Tape measures allow for longer measurements than regular rulers. Both systems are generally shown on tape measures. Calipers go where rulers and tape measures cannot. There are two main types of calipers: open-jawed and Vernier. Open-jawed calipers are opened to take the measurement, then put against a ruler to get the measurement number. Vernier calipers are more precise because the measurement scale is right on the tool.
Friction
and
gravity
keeps us grounded.
Friction
is "a force that exists between any two surfaces that are in contact with each other. This force resists the motion of the two surfaces." (Friedhoffer, 26) This friction will build up heat. To reduce friction lubricants can be added. "Lubricants coat surfaces that are in contact with each other . The surfaces then ride on a thin layer of the lubricant." (30) This reduces heat and wear on the two opposing surfaces.
While gravity keeps us grounded,
inertia
keeps us moving. Sir Isaac Newton's first law of motion states the following: "An object in motion will stay in motion in a straight line unless acted upon by an outside force, and an object at rest will stay at rest unless acted upon by an outside force." (34) Without gravity, later explained, a bullet shot from a gun would continue forever unless it came upon something to stop it. Gravity is the outside force that acts upon it to bring it to the ground. The second part of the law means that unless the bullet is fired from the gun or unloaded, it will stay in the chamber forever. It isn't going anywhere unless acted upon by an outside force. A force is a push or a pull exerted on an object. Amusement parks take advantage of force, motion and friction to provide stimulating rides for park-goers. Imagine being on an anti-gravity merry-go-round that didn't have any friction - you'd go on forever or slip out of your restraint.
There are many simple machines everyone should know how to use. Many of us just use them without fully understanding the scientific principle behind them. A screw works better than a nail because it grips, but most people are satisfied just pounding in a nail into the wall and hanging a picture. So, if we understand the basic scientific principles behind these simple machines we will make better choices when it comes to our own lives. Here are the simple machines we are going to look at: the inclined plane, the lever, the wheel and axle, and the pulley.
If you have ever walked up a ramp you have had experience with an
inclined plane
. This simple idea is put to use in many wonderful ways. As mentioned before, the screw is an example of an inclined plane at work. Even a nail utilizes inclined planes. Its head is chiseled to a point. There are many inclined planes coming together. This allows the nail to go into the wood. "Inclined planes take advantage of the fact that pressure is multiplied as the surface area decreases." (39). With a dull nail, more force is needed because the surface area of the point is increased. A sharp nail needs little force to do the job. Axes, hatchets and mauls take advantage of the inclined plane also. Two inclined planes come together to create a sharp cutting edge. When swung, the maul (large axe), the axe and hatchet (a small axe) utilize moving inertia and the inclined plane to chop. The splitting wedge is used in combination with a sledge hammer. "The inclined planes on either side of the blade force the log to split apart."(40) The ladder is also an inclined plane because in order for it to be useful it needs to rest against something. Stairs are also an inclined plane. A screws' threading creates an inclined plane that helps hold things together. Many simple experiments can be done with screws and other inclined planes. The students might hypothesis on the effect of changing the slant of the inclined plane and its efficiency. For example, decreasing the inclined plane on a screw will allow for a stronger hold in a wall.
The
lever
is also seen everywhere. "A lever is a bar that turns about a pivot point and is used to transfer and/or multiply force." (52) A fulcrum is the pivot point of a lever. It is the point where the balance is needed to lift or move an object. "Levers can help you to multiply input force when you want to accomplish work." (Ibid) There are many different types of levers, each with its own mechanical advantage. An example of a first-class lever is the see-saw. The first-class lever is helpful in "magnifying force and distance." (Ibid) The claw hammer and the pry bar are also good examples of first-class levers. Scissors are two connected first-class levers that have long handles so that the force exerted is magnified at the cutters. The second-class lever has the fulcrum at the other end and force is exerted up at the free end to lift the resistance. The wheel barrow is a perfect example of this type of lever. The third-class lever has the fulcrum at one end, with the input force in the middle and the force pushing down. The hammer, as a nail driver, is this type of lever. Picture your hand holding the hammer. This is the fulcrum (your wrist). The head of the hammer is the force and the head of the nail is the resistance. The input force is your hand moving down.
The
wheel and axle
is a very identifiable tool set that reduces friction to aid in the carrying of objects while magnifying input force and speeds. "As the wheel rotates, the outer portion of the wheel (the circumference) moves a greater distance than the inner portion of the wheel. This greater movement provides a mechanical advantage." (67) There are many different experiments that can be done with the wheel and axle. Take a faucet. If you take the knob off it is almost impossible to turn the water on. But once the knob is replaced, the force exerted on the knob is magnified at the center, thereby turning the water on. There are many types of wheel and axle mechanisms. Casters, the wheelbarrow, the screwdriver, the circular saw, and the hand drill are all types of wheel and axle tools. The hand drill's wheel is special because it contains gears. A gear has teeth which decrease slippage. Gears can mesh with other gears or a chain, such as in a bicycle or chainsaw. "Gears can increase the mechanical advantage and change the direction of the input forces." (75)
Pulleys
exist in almost all houses. A pulley utilizes the wheel and axle idea to change the direction of an applied force. A rope or cable is wrapped around a wheel which is attached to a bale (a cage-like device) that is attached to an axle. A clothes line is a simple pulley. You pull on one side and the other side moves away and vice versa. Window shades some times utilize small pulleys with ropes. A compound pulley (block and tackle) is used to "multiply and change the direction of an applied force." (80) Many pulleys are put together so that the task is easier. The only difference is that the rope must be longer and you must pull farther, not harder. It decreases the effort needed (work) to lift larger objects.
Many of the above tools work well alone. However, as technology evolved, it became more and more evident that combining these tools increased output while decreasing the effort needed. Adjustable wrenches, vises, vise grips, and bolt cutters take advantage of the combination of simple tools. It utilizes both the lever and the inclined plane. The arms work as compound levers, while the cutting edges are inclined planes. The input force is magnified as the two levers (handles) are brought together, which bring together the two steel inclined planes. This makes for a tool that cuts through bolts.
Ideas for Projects
Before going out on their own, students should have a basic knowledge of how to use simple tools. For the unit students will be asked to discuss how the object utilizes one or more of the above concepts. The following is a partial list of typical objects. The list can be expanded to meet the needs of the classroom.
-
- Automobile -- a very exhaustive project. You might want to narrow.
-
- Chainsaw
-
- Bicycle
-
- Lock and key
-
- Can opener
-
- Zipper
-
- Fishing Rod
-
- Nutcracker
-
- Nail clippers
-
- Bathroom Scale
-
- Manual Typewriter
-
- Water wheel
-
- Wind mill
-
- Dentist's drill
-
- Manual Lawn mower
-
- Mechanical Clock
-
- Lawn Sprinkler
-
- The Sewing Machine
-
- Block and tackle
-
- Tower Crane
-
- Escalator or Elevator
-
- Hand drill
-
- Combine Harvester
-
- Window Shade
-
- Car Seat Belt
-
- Apple Peeler
-
- Winch
-
- Car Brakes
-
- Yo-Yo
-
- Screwdriver
-
- And anything else mentioned in the material above
All of the objects above employ the physics concepts described, most in combination with each other. Students should be able to identify and explain most of the concepts used in their chosen object. Many of these can be found fully explained in David Macaulay's The New Way Things Work, which comes in CD-Rom or book form. Students can explore the medium of their choice. If possible, the CD-Rom version is useful for whole class introduction. Having on hand a simple tool kit that has examples of each of the simple machines would be extremely beneficial to student learning. Also, www.howstuffworks.com is a great site that shows how things work with pictures and simple explanations. (They also offer a CD-Rom.) You would need a connection to the internet to access this material.