Physics Teacher's

Interactive Science Simulations

2010-02-07T17:29:00.000-10:00

Fun, interactive, research-based simulations of physical phenomena from the PhET project at the University of Colorado.

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Quantum Phenomena
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Radioactive : Power

Waves in a Ripple Tank: A Virtual Activity

2009-01-11T17:00:00.006-10:00

Waves in a Ripple Tank: A Virtual Activity

Go to the site http://www.falstad.com/ripple/. A “Ripple Tank Applet” window will open that runs a simulation of waves generated in a ripple tank.

By “clicking on” any or all of the three task bars in the upper right hand corner of the applet window, you can change the type and number of wave sources. The third task bar allows you to use the mouse to edit the waves or walls (barriers). You can adjust the speed, resolution, frequency, brightness, and/or damping of the wave simulation to obtain a clearer representation of the wave phenomena. A complete and detailed set of directions for how to use this simulation is linked to the web page.

Your task is to use this web site to identify and investigate various wave properties and characteristics. You will hand in pictorial representations of…

Circular Wave
long wavelength
shorter wavelength
Plane Wave
long wavelength
shorter wavelength
Reflection
Plane Wave Off Angled Straight Barrier
Plane Wave Off Concave (Parabolic) Barrier
Circular Wave Off Straight Barrier

Diffraction
Plane Wave Around a Barrier
Plane Wave Through an Opening
Circular Wave Around a Barrier
Circular Wave Through an Opening
Refraction of a Plane Wave
Refraction due to Temperature Gradient (simulates sound wave over lake)
Interference
Two Circular Waves (wide spacing between sources)
Two Circular Waves (closer spacing between sources)
One Plane and One Circular Wave (this is a tricky one to simulate!)
Single Slit (plane wave)
Double Slit (plane wave)
Triple Slit (plane wave)
Doppler Effect
Beats
Something else you find really interesting

You have two options for completing this assignment:

· Make small (about 4 in. x 4 in.) sketches with colored pens/pencils…OR…
· Use a “screen capture” program to copy and paste the actual images from the applet window into a document (MS Word with text boxes, for example), which can then be saved and printed.

You can download a free trial version of an easy to use screen capture program at http://www.etrusoft.com/. The image shown on this handout was “captured” using this program.

Another option is to use the “print screen” function on the keyboard and then paste the picture in your report. Pressing “print screen” (Prnt Scrn) on the keyboard copies the entire screen, so you may want to enlarge the ripple tank window to fill the entire screen.

You can probably fit 6 diagrams/sketches on each side of a page. Be sure to label each sketch.

HOME

2008-12-30T18:54:00.006-10:00

Physics Note
Try our new section to study physics... Are you a student in a physics class? • See our Physics homework help section.

Science Project and Experiment For All Students - Teacher: Free ...
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TRIAL EXAM - Test. Access to this blog will keep students and teachers well informed of the latest development of Exam Paper. Students can also access the ...trialexam.blogspot.com

Physics

2008-12-25T23:09:00.002-10:00

Physics (Greek: physis – φύσις meaning "nature") is the Physics (Greek: physis – φύσις meaning "nature") is the natural science which examines basic concepts such as energy, force, and spacetime and all that ...en.wikipedia.org/wiki/Physics - 231k

The Physics Classroom is an online interactive tutorial of basic physics concepts. The lessons use an easy-to-understand language to present common physics ...www.physicsclassroom.com/ - 6k

dir.yahoo.com/Science/Physics/ - 18k - Simpanan sementara - Laman-laman serupa
Eric Weisstein's World of Physics
Online encyclopedia of physics terms and formulas. Full searchable, and also browsable alphabetically and by topic. Part of Eric's Treasure Troves of ...scienceworld.wolfram.com/physics/ - 9k - Simpanan sementara - Laman-laman serupa
Physics 2000
An interactive journey through modern physics. Have fun learning visually and conceptually about 20th century science and high-tech devices.www.colorado.edu/physics/2000/ - 2k - Simpanan sementara - Laman-laman serupa
Physics The WWW Virtual Library
Resources pertaining to the physics of sound, noise control and soundproofing. ... An actively maintained collection of space physics links. ...vlib.org/Physics - 9k - Simpanan sementara - Laman-laman serupa
Physics - spotlighting exceptional research
Let us know what you think of Physics. Please email physics@aps.org with your comments, ideas, or suggestions for topics. You may wish to consult our FAQ ...physics.aps.org/ - 20k - Simpanan sementara - Laman-laman serupa
physicsworld.com
Physics news, jobs, equipment buyer's guide, and events.physicsworld.com/ - 34k - Simpanan

How to Keep Your Computer Safe From Viruses

2008-12-20T16:18:00.001-10:00

As more and more people are becoming at ease using their computers at school, home or in the office it’s merely a matter of time before they meet a computer virus. Here are our top instructions to guard you from computer viruses. Use a high quality anti-virus program. There are many diverse anti-virus computers programs on the market some of them are better than others. Look to trustworthy computer magazines or websites for ratings to aid you locate the one that matches your requirements. Always use your anti-virus software. Keep your antivirus programs up to date. Most programs come with a yearly subscription make sure you take benefit of the updates. More advanced programs allow you to schedule updates or complete system scans for “off hours” like 2AM when you aren’t expected to be using your computer. Keep your computer up to date. From time to time operating systems fall victim to security holes or issue updates. Make sure you check occasionally to make sure you are running steady latest versions of your software. If you use floppy disks or USB drives on public computers like your school computer lab, Kinko’s, or even digital photo printing store make sure you scan them for viruses. Public computers are notorious for not being up to date and properly protected. Be wary of email attachments. Never open attachments from people you weren’t expecting. Also be careful of attachments from people you know but weren’t expecting. Many computer viruses replicate themselves by reading the contacts from an infected computer. Use text email if possible. Use downloaded freeware and shareware files or software with caution. Try to download them from popular reputable sources that scan the programs before they are uploaded. To make sure you are safe scan the program before you install it on your computer. Be wary of links in IM or instant messaging software. Don’t accept invitations from people you don’t know and never click a link from someone you don’t trust, they can easily redirect you to another website that will try to install a virus on your computer system

UNDERSTANDING PHYSICS.

2008-12-16T07:04:00.001-10:00

Look outside the window and you may see the leaves of a tree falling down.
There will some students who would not even have noticed the leaves falling. Some may have seen the falling leaves but this not register what they saw. Other may admire the beauty of the falling leaves .
Still others may ask some questions about the falling leaves;
• Why did the leaves fall down and not to fly up ?
• Would the larger leaves fall faster ?
• Would a heavier leaf fall faster?

In fact there are a thousand and one questions you can as about the falling leaves.
The leaves of a tree falling down is one of the events that happened around us everyday
Event –something that happens, in this case the leaves falling from the tree. An action, with a beginning and an end.

Physical phenomena are always unfolding before us. By asking questions we can focus on the aspect we are interested in. By making observations and careful measurements we can gather the necessary data that will help us in our search for the answers to our question. Experiment have to properly planned and carried out to verify the answer we seeks.
In physics we learn about making connections. We know that when released the object,it fall down towards the earth. We observe that the Moon goes round the Earth. Is there any connection between the two phenomena ?

Physics is a branch of science centered on the study of the matter, energy, and the connection between them.ExampleThree students have performed an experiment in which they tested the sinking and floating behavior of three objects , each of the same volume but of difference mass. They found two of the object sank while the third object floated. Consider the following discussion among them.

Q. Why should I have to study physics if I'm going to be a doctor - lawyer - etc?
Physics, as a discipline - especially at an undergraduate level, teaches many things that are important in all walks of life:

1) Problem Solving skills - the typical physics course is more problem solving based than any other subject (except perhaps mathematics) and the problems are often more practical. If you want to be a doctor, say, skill at quickly thinking about the problems of "what is wrong with this patient" could mean the difference between life and death.

2) Real World Familiarity - Freshman physics courses tend to teach about the every-day, real, world. You learn about how things move, how they fall, what friction means, what constraints conservation of energy and momentum can put on a system.

3) Relevant information - Physics is directly relevant to the core of many fields which might seem separate at first glance.

Engineers build bridges, but they need to understand the forces involved and how bridges react to stress in order to build safe ones.
Biologists look at proteins and DNA - the structures of which are measured using diffraction techniques developed by physicists, and only really understood through physics. Biologists also use light and lasers to make fluorescence measurements to keep track of the chemicals present - physics illuminates the devices, lenses, microscopes and the very colors of the dies used!

As you can see, there are many good reasons to study physics, no matter what your career goal might be - but the most important is that physics is constantly unveiling new facts about our universe - from the very small, like new semiconductors and superconductors, to the very large, like black holes and galaxies - do you want to understand what is coming, or do you want to be left behind?

The Oceans' Wave Power

2008-11-26T15:43:00.001-10:00

For more than 200 years inventors worldwide have filed patents for wave-power technology of a dazzling variety of designs-bobbing objects ("ducks"), buoys, articulated rafts, floating bags, overspills, and many others. There has been no shortage of ideas. Many of these ideas are in fact technically feasible, so it seems a shame that this renewable energy resource has not been much used. The main challenge is building a system that is economically attractive when so many other forms of energy production (nuclear, fossil fuels) receive subsidies and already have infrastructure in place. There are some wave power systems in place around the globe: the Faroe Islands; Islay, Scotland; Oahu, Hawaii (providing power for the U.S. Marine Corps. base there); Santo, Spain; Portugal; and even the world's first commercial "wave farm" in England.
The World Energy Council has estimated that wave power could produce as much energy in a year as 2,000 oil, gas, coal and nuclear power plants' twice the amount of electricity produced worldwide-by generating as much as 2 terawatts (that's 1 trillion watts).
Not every place is a candidate for wave power generation. Prime locations identified are Scotland, northern Canada, southern Africa, and the Atlantic Northeast and Pacific Northwest of the United States. Experts have estimated that wave-power systems in the Pacific Northwest alone could generate up to 70 kW per meter of coastline.

Typical Designs

Wave-power systems can be located onshore or offshore, and come in a surprising range of designs. There are currently four basic "capture" methods: point absorbers (largely vertical, with a relatively small footprint on the surface); attenuators (horizontal footprint, arranged parallel to the waves to undulate with the flow); terminators (perpendicular to the waves); and overtopping (perpendicular to the waves, which break over the system). There are different power take-off systems including hydraulic ram (water hammer pumps water above the starting point); elastomeric hose pump (peristaltic, like your intestinal tract), pump-to-shore, hydroelectric turbine, air turbine, and linear electrical generator. Here are some systems already in operation, or close to it:

OFFSHORE: POINT ABSORBER SYSTEMS
1. The Salter "Duck"-In 1970 Stephen Salter ("the father of wave power"), a professor at the University of Edinburgh, designed a wave-power device that could both stop 90 percent of the wave motion and convert 90 percent of that into electricity, a standard that all other designed continue to be measured against. Ironically, the Duck itself never went into use. During the 1990s, a project based on the Duck and dubbed the OSPREY (Ocean Swell Powered Renewable Energy), commenced in the Clyde Estuary of the Scottish coast. Capable of generating 1 mW of power, the OSPREY was on its way to becoming an unqualified success until Hurricane Felix came along and sunk it (at great expense in terms of both money and confidence).
2. The AquaBuOY wave energy device-AquaBuOYs (Finivera Renewables) really do look like navigational buoys, and this is no coincidence. Obviously, maximum output from a wave-power device should be during those times when the waves are at their highest, but if the technology can't withstand rough seas (as with the OSPREY, above), they aren't much good. Operating on the premise that since navigational buoys can survive for decades in all sorts of conditions, the AquaBuOYs were designed to ride the waves for an estimated 100 years. The vertical wave action drives a two-stroke hose pump that directs pressurized seawater into a turbine connected to a generator; the resulting power is sent via an underwater transmission line. While at least four projects are in the permitting process (including one in Makah Bay, WA), as of this writing.
3. PowerBuoy "Like the AquaBuOY above, the PowerBuoy resembles a navigational buoy, although one with long cylinder extending far below that houses the mechanics of the system. These PowerBuoys (Ocean Power Technologies) are placed from one to five miles offshore in 100 to 200 feet of water, and can be ganged together to form a "wave-power farm" such as the one to be installed off the coast of Santo, Spain. That 1.39MW station will have one 40kW and nine 150kW PowerBuoys.

OFFSHORE: ATTENUATOR SYSTEMS
1. Pelamis - Ocean Power Delivery, Ltd., developed world's first commercial offshore wave-power facility using its Pelamis Wave Energy Converter, a string of steel cyclinders hinged to articulate. It lies half-submerged, like a 150-meter-long, bright red sea snake (pelamis is the genus for the sea snake), more or less facing into the waves. The cylinders contain hydraulic pumps activated by the wave action; the electricity comes as high-pressure oil gets pumped into generators. The first phase of the wave farm, located 5 km off the coast of Portugal, comprises three 750kW Pelamis "snakes" that combined to generate 2.25 MW; another 28 are expected to be added, bringing the total power generated to 22.5 MW'enough to provide electricity for more than 15,000 homes.

OFFSHORE: TERMINATOR SYSTEMS
1. Nearshore OWC-This is an offshore version of the Limpet, described below.
OFFSHORE: OVERTOPPING SYSTEMS

1. Wave Dragon-Overtopping systems work very much like hydroelectric dams, using the potential energy of water stored at an elevation higher than the turbines it drives. The Wave Dragon overtopping system funnels the waves into its own reservoir to create a head; the water is then released through channels that contain turbines. The Wave Dragon is moored 25 to 40 meters offshore in deep water, somewhat like a floating beach.

ONSHORE: OSCILLATING WATER COLUMN:
1. Limpet (Land Installed Marine Powered Energy Transformer)- This an oscillating water column (OWC) system to convert the waves' kinetic energy to electrical power. Picture a box with the open end submerged but slightly tilted toward the incoming waves, with air trapped inside the box. Now imagine there is a narrow outlet for this air, and inside this tube is a turbine. As the waves raise the level of the water inside the box, the air rushing in and out of the tube powers the turbine. A Limpet system (WaveGen) in Islay, Scotland, uses an inclined oscillating water column (OWC) system optimized for the area's anverage annial wave intensity, and feeds a pair of 250kW generators. The Limpet power station in the Faroes is very similar. WaveGen also designs a near-shore oscillating water-column system.
There are many companies designing wave-power systems using these and other designs (such as the tapered channel system, an onshore system, and the pedulor system, an offshore device), and new ones seem to come along frequently as more countries come to recognize the potential of wave power.

Wave Power Advantages
1. Wave energy is an abundant and renewable resource. 2. Even though not every country has coastline, the combined potential output of wave-power generation would meet all the electricity needs of the world. 3. Although the equipment represents a substantial investment, the "fuel" is free and not confined by geopolitical boundaries. 4. The effect on the environment is deemed to be minimal.

Wave Power Disadvantages
1. These are most effective near coastlines, of which there is a finite supply. 2. Large scale systems are still in the early stages.

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Science discovery- used physics to build a flying machine

2008-11-17T22:39:00.001-10:00

Some scientific developments, and the inventions resulting from them, are so important that they change people's lives all over the world. In 1903, two brothers from Dayton, Ohio, USA, managed to solve a problem that others had failed to conquer for hundreds of years. They were Wilbur and Orville Wright and the problem was how to build a flying machine. The Wrights made many scientific studies of the shapes of wings, the way propellers work, and how to control an aircraft in flight. They carried out the first true powered airplane flight on 17 December, 1903 at the coastal sand dune area of Kitty Hawk, North Carolina, USA. Their invention of the plane transformed our world.

Soon after the Wright's early flights, many other craft took to the skies. First to fly across the Channel between France and England was Louis Bleriot, in 1909. Soon people began to see the potential for planes as passenger-carriers, beginning the era of fast long-distance travel.

The Wright's first plane, the Flyer, was powered by a small petrol engine that the brothers had designed themselves. They knew that the
petrol engines of the time, built for the early motor cars, were too heavy for an aircraft. Over the following years they built improved
versions of the Flyer and made longer flights.

History of Computer

2008-11-16T03:18:00.001-10:00

A COMPUTER IS AN ELECTRONIC MACHINE that manipulates, changes and processes information, or data, of all kinds - not only numbers but also words, patterns, pictures, animations, sounds and so on. The data is processed called a program, which tells the computer what to do. Inside a computer, the program according to a sequence of instructions and data are in digital form, as patterns of tiny electrical signals that pass around the many circuits and microchips. Computers can deal with vast amounts of information in a very short time. For example, a supercomputer can work out all the consequences of more than 200 million chess moves every second.

Supercomputers A supercomputer must work so fast that its main processing and memory circuits are supercooled to many degrees below freezing. Supercooling reduces the resistance of the conductors in the electronic circuits.

In the 1830s English mathematician Charles Babbage (1792-1871) designed several kinds of programmable mechanical calculators. His machines used gearwheels to do the calculating and had more than 2,000 moving parts. Due to engineering and money problems, Babbage's machines were never finished at the time. But modern computers still use his basic ideas.

Physics Teacher - Electricity Network

2008-11-13T18:01:00.000-10:00

ELECTRICITY IS AN INVISIBLE form of energy. It is based on the tiny charged particles inside atoms. In an atom's nucleus, particles called protons have a positive charge. Whizzing around the atom's nucleus are electrons, which have a negative charge. Normally, the positive and negative charges balance. If they become unbalanced, an electrical force is produced. This may stay in one place, as static electricity, or move from place to
place, as a flowing current. Electricity is so useful to us because it can flow along wires to
wherever we need it, and be changed into other forms of energy such as light, heat and movement.

The electricity network

Power stations turn the energy of movement into electrical energy which is medium strength, or mid voltage. This is changed into more powerful, high-voltage electricity and sent along large cables or wires, high on pylons or buried underground. This network of cables and wires is called the electricity distribution grid. The electricity is changed back into lower-power forms, industrial and mains voltage, for use in factories, farms, offices and homes.

Electricity in atoms

Everything is made up of trillions of incredibly tiny particles, called atoms. An atom has a central nucleus containing protons, each with a positive charge, and neutrons, each with
no charge, or neutral. Going around the nucleus in empty space are much smaller particles, called electrons, each with a negative charge. When atoms or substances gain or lose electrons, they become electrically charged. Gaining electrons makes them negative. Losing electrons makes them positive.

Electricity at work

If there was a power cut in this city, people would have to manage without most of their lighting and heating, and the machines that make their lives so much easier. Daily routine would grind to a halt and the only sources of energy would be batteries, candles, wood, coal or gas. Yet people managed without electrical devices for thousands of years, and still do in many parts of the world. It is only in the last century or so that electricity has been put to work. One of its great advantages is that it is available at the flick of a switch.

Physics Tips For SPM 2008

2008-11-08T21:01:00.001-10:00

For All Students STEP 2008

Chapter 1 : Sub-topic - Measure instruments
Chapter 2: Sub-topic - Momentum, impulse / impulsive force and Forces in Equilibrium
Chapter 3 : Sub-topic- Gas Pressure -atmospheric pressure and Pascal's Principle
Chapter 4: Gas Law - Experiment Heat Capacity/ latent heat/ Thermometer
Chapter 5: Refraction of light/ understanding lenses

Chapter 6: Interferens of Waves
Chapter 7: Ohm law, Relationship between I and V
Chapter 8: Electromagnetic Induction/ Application
Chapter 9: LOgic gates and Semiconductor diodes
Chapter 10 : Radioactive and Isotop/ Nuclear Energy - Nuclear Fusion

Science Discovery

2008-11-08T02:23:00.000-10:00

Amedio Avogadro (1776-1856) worked as a lawyer before taking up science and becoming professor of physics. In about 1811, he imagined a row of the same-sized containers. Each held a different gas, but at the same numbers of molecules in each container. This is now known as Avogadro’s law-equal volumes of all gase, when at the same temperatures and pressure, have the same numbers of atoms or molecules.

Composites

2008-11-04T04:37:00.001-10:00

Materials science is a fast growing area of science, especially in engineering. It involves taking various raw or ingredient substances and making them mix, combine or react together in various ways, to produce a new material with specialised properties. Each of the ingredient substances has some useful features, and these all add together to produce the final material. One example is glass-reinforced plastic, GRP. This is made by embedding tiny fibres of glass into a type of plastic. The plastic gives overall bulk and flexibility, while the glass fibres provide extra strength, stiffness and resistance to wear. GRP is used to make boat vehicles, aeroplanes, and factory and office equipment.

Space tiles- the tiles on the undersides of space shuttles are made of heat-resistant ceramic composites. As the shuttle comes back from space into the Earth’s atmosphere, friction with the thickening air generates enormous heat. The tiles keep this heat out of the shuttle’s interior. They are checked and renewed as necessary after each mission.

Strong as steel…most valuable metal

2008-11-02T14:44:00.000-10:00

The world’s industriies use millions of tonnes of steels each year. Steel plate form the lrge panels in washing machines, car, trains and ships. The stainless steel used for making cutlery is an alloy with at least one-tenth of the extremely hard , shiny metal known as chromium. Steel with titanium in them form the light but stiff structure sheets in high-speed aircraft. Gold is a famous symbol of wealth. But rarer metals such as platinum and palladium command higher prices for specialised engineering and electronic uses.

Keyword : Physics Teacher's, Trial Exam

Floating ice

2008-10-31T17:36:00.001-10:00

Most subtances enlarge or expand as they heat up, and becomes smaller or contract as they get colder. But water is unusual. It contracts as it cools down to 4 0C. Then, as it gets even colder and freezes into ice, it expands again. This means a lump of ice at 00C weighs less than the same sized lump of water at 100C. So ice from an ice cube in a drink to a giant iceberg in the ocean- floats on water.

Energy from the Sun

2008-10-27T03:50:00.001-10:00

The energy we receive from the Sun is called solar energy. It consists mainly of light and heat that travel through space. These forms of energy come from atoms smashing into each other in the centre of the Sun and joining together, or fusing. This process is called nuclear fusion as we study in form 5. Energy thar comes from the centres or nuclei of atoms is called nuclear energy. The form of nuclear energy in nuclear power stations here on Earth comes from nuclear fission, when atoms split apart.

High and Low Sounds

2008-09-18T13:05:00.002-10:00

THE PITCH OF A SOUND means how low or high it is. In a music band,
the bass drum's deep boom is low-pitched, while the triangle's shrill tinkle is high-pitched. Pitch depends on how many times the sound source moves to and fro, or vibrates, each second. This
is the same as the frequency - how many sound waves are produced each second. The frequency of a wave is measured in units called Hertz, Hz. For example, the note of middle C, in the
middle of a piano keyboard, has a frequency of 261 Hz. Frequency is related to wavelength, since higher frequencies have shorter waves. The length of a middle C sound wave is 126 centimetres.

What sounds can we hear?

We hear many sound frequencies, from the shrill notes of bird song to the deep growl of traffic. But, because of the way our ears work, we do not hear all of the sounds around us. Our ears pick up frequencies from about 20 to 20,000 Hz (Hertz, vibrations per second). We hear sounds below 80 Hz as low, deep booms, thuds or rumbles. Frequencies below about 30 Hz may not be heard clearly, but if they are powerful enough, we can feel them as vibrations in the air and ground. Our ears are most sensitive in the range from 400 to 4,000 Hz. (Human speech tends to be around 300-1,000 Hz.) Sounds above about 5,000 Hz are extremely high-pitched squeaks, hisses and screeches. As people get older, their ears become less sensitive to high notes. So a young person can hear a bat's very high-pitched squeaks, while an older person cannot.

Telecom network

2008-09-15T02:44:00.001-10:00

A mobile phone sends and receives messages by radio waves. The radio waves travel to and from a tranceiver (transmitter/receiver) station which connect the call into the standard telephone network. Countries are divided up into different areas, called cells, and each cell has its own tranceiver station. In an areas where a lot of people live, there are many small cells because there likely to be many people using mobile phones. In sparsely populated areas populated areas, the cells are larger.

Inside a mobile phone

A "mobile" is a low-power radio transmitter-receiver. It has mouthpiece to change sound waves into electrical signals (like a microphone), and an earpiece to change electrical signals into sound waves (like a loudspeaker). The transmitter-receiver only needs to send and pick up waves from the nearest cell tower, which is usually just a few kilometres away. However hulls or tall buildings may block the radio signals. also, in areas where the cell towers are farther apart, the signals may be too weak to travel to and from the phone.

Simple Machines

2008-09-13T04:00:00.001-10:00

Every mechanical device, even the most complicatrd giant earthmover, is made from only four different types of simple machines. These are the lever, the inclined plane or ramp, the wheel and axle, and the pulley. The lever ia a stiff beam or bar that pivots at point called fulcrum. If the fulcrum is closer to one end than the other, you can use the lever to lift a heavy weight more easily. The inclined plane (ramp or slope) is a machine to. It is usually easier to slide a heavy weight up a slope than to lift it straight up. Place two inclined planes back-to-back and they form a wedge, as in a knife blade, axe or chisel. A wedge wrapped around a rod, in the corkscrew-like shape called a helix, forms a screw. Screws are used to lift things and fasten them together.

Building the pyramids
The pyramids were built in ancient Egypt about 4,500 years ago, from thousands of blocks of stone-some weighing many toones. These may have been levered into place, or dragged up a slope built beside the pyramid, or rolled up on logs. No-one really knows.