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| Henry_Greenside\'s_Duke_Physics_Challenges Physics-related word-problem puzzles. |
| How_Atoms_Work Shows how man determined the structure of the atom and learned how atoms interacted with each other. |
| How_Things_Work A service providing answers to questions about physics, science, and how things in the world around us work. Companion to the book by the same name. |
| How_to_Study_Physics A University of Texas classic, written before the web was around, but now revised and web-ready. |
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| I_Love_Physics_Forum Discuss physics education and related topics that come up in discussions about physics. |
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| Institute_of_Physics_(IOP)_-_Teaching_Physics_in_Schools_and_Colleges A website aimed at those with an interest in the teaching and learning of physics in schools and colleges. The site provides visitors with information about the current activities of the IOP educatio |
| Interactive_Physics_Review A study aid for some basic Newtonian physics concepts that come up early in a student's study of basic college level physics. |
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| Interactive_Textbook College freshman-level physics textbook online in several different formats, notably a java-interactive format. |
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| Intuitor_-_Insultingly_Stupid_Movie_Physics Reviews and rates Hollywood movies for bad physics content. |
| ISU_Physics_Teacher_Education_Program From Illinois State University. |
| Kenny_Felder\'s_Math_and_Physics_Help_Page A collection of papers written to explain various concepts in math and physics, as well as papers generously donated by other people. |
| MIT_OpenCourseWare_-_Physics Undergraduate and graduate courses available for noncredit study and review. Materials provided may include syllabi, reading assignments, videotaped lectures, problem sets with solutions, lecture not |
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| Physical_Science_Resource_Center_(PSRC) This site has plenty of resources for physics and physical science teachers K-16. |
| Physics_2000 An interactive journey through modern physics. Have fun learning visually and conceptually about 20th century science and high-tech devices. Uses java applets. |
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| Physics_Central The outreach site of the members of The American Physical Society. Find out how physics is part of your world, ask questions on how things work, see physics in pictures, get updates on physics in the |
| Physics_Comics Comics-style lessons in physics fundamentals. Topics include motion, forces, vectors, work and energy, and impulse and momentum. |
| The_Physics_Encyclopedia This site provides exhaustive, comprehensive, carefully selected and structured lists on Internet physics resources. |
| Physics_Equations_and_Constants A concise guide to equations and lists of constants and basic facts at the high school level, sorted by topic. |
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| Physics_Simulations_in_Education ZIP-format files for DOS or Windows covering a variety of physics phenomena and applications. |
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Simple Machines:
These devices were all in common use for centuries before Leonardo's time. Each one makes work easier to do by providing some trade-off between the force applied and the distance over which the force is applied.
Wheel and Axle
In this machine a wheel or spoke is locked to a central axle so that when one is turned the other must turn. A longer motion at the edge of the wheel is converted to a shorter more powerful motion at the axle. In reverse, a short powerful force at the axle will move the wheel's edge a greater distance.
Pulley System
A single pulley simply reverses the direction of a force. When two or more pulleys are connected together, they permit a heavy load to be lifted with less force. The trade-off is that the end of the rope must move a greater distance than the load.
Wedge
A wedge converts motion in one direction into a splitting motion that acts at right angles to the blade. Nearly all cutting machines use the wedge. A lifting machine may use a wedge to get under a load.
Screw
A screw is a central core with a thread or groove wrapped around it to form a helix. While turning, a screw converts a rotary motion into a forward or backward motion.
Lever
A lever is a stiff rod that rotates around a pivot point. Downward motion at one end results in upward motion at the other end. Depending on where the pivot point is located, a lever can multiply either the force applied or the distance over which the force is applied.
Other Elements of Machines:
Though these devices were also used in machines in Leonardo's time, he experimented with them and made changes to improve how they worked. He also combined them in many exciting new ways to create machines and inventions that had never been seen before.
Gears
Gears are toothed or pegged wheels meshed together to transmit motion and force. In any pair of gears the larger one will rotate more slowly than the smaller one, but will rotate with greater force. Each gear in a series reverses the direction of rotation of the previous gear.
Bevel Gears
Gears that mesh at an angle change the direction of rotation.
Worm Gear
A worm gear is a combination of a gear meshed with the threads of a screw. This combination changes the direction of turning motion by ninety degrees. Worm gears also decrease the speed of turning from screw to gear and increase its force.
Rack and Pinion
A single gear, the pinion, meshes with a sliding toothed rack. This combination converts rotary motion to back and forth motion. Windshield wipers in cars are powered by a rack and pinion mechanism. A small pinion at the base of the wiper meshes with a sliding rack below.
Cam
A cam is a wheel with shaped bumps on it. Cams are often connected to rods, levers, or springs. In the gravity trip hammer shown here, the bumps on the turning cam push down on the end of the lever making it raise the hammer again and again.
Crank and Rod
The crank is a wheel with a pivoting arm attached near its edge. The arm is attached by a hinge to a rod. When the crank turns, the rod is pushed back and forth. Alternatively, if the rod is pushed back and forth at the right speed, the crank will turn. The crank and rod shown here are part of giant steam engine.
Chains and Belts
A chain or belt connects two separated wheels so that one turns, the other will turn in the same direction.
Ratchet
A ratchet is a device that allows a wheel to turn in only one direction. The ratchet wheel has specially shaped teeth. A bar on a pivot called the "pawl" is fixed above the ratchet wheel. The pawl slides over the teeth of the ratchet in one direction, but blocks the motion of the teeth if the wheel turns in the other direction.
Now that you have seen the various elements of machines, you can try to figure out which ones are used in some common devices by going to the Gadget Anatomy page.
Science Learning Network /
email: sln@mos.org /
© 1997 The Museum of Science
