FORCES, SIMPLE AND COMPLEX MACHINES
What do these pictures tell you? What do they have in common?
ACTIVITY Underline or find the following words in the following texts. Force Kick Exert Push Move
CONTACT FORCE Everyone has a basic understanding of the concept of force from everyday experience. When you push your empty dinner plate away, you exert a force on it. Similarly, you exert a force on a ball when you throw or kick it. In these examples, the word force is associated with muscular activity and some change in the velocity of an object. Forces do not always cause motion, however. For example, as you sit reading this book, a gravitational force acts on your body and you still remain stationary. As a second example, you can push (in other words, exert a force) on a large boulder and not be able to move it.
SIMPLE MACHINES
Once upon a time a person needed to move something heavy Once upon a time a person needed to move something heavy. He or she picked up a long stick and stuck it under the edge of the heavy object and then pushed down on the other end of the stick. And the first simple machine was invented. Simple machines are just that. The simplest form of using one thing to accomplish something faster or better. A tool. They were the first ones created and we still use them today.
A pulley is a simple machine that uses grooved wheels and a rope to raise, lower or move a load.
Pulley are wheels and axles with a groove around the outside A pulley needs a rope, chain or belt around the groove to make it do work
LEVER A lever is a stiff bar that rests on a support called a fulcrum which lifts or moves loads.
Levers-First Class In a first class lever the fulcrum is in the middle and the load and effort is on either side Think of a see-saw
Levers-Second Class In a second class lever the fulcrum is at the end, with the load in the middle Think of a wheelbarrow
Levers-Third Class In a third class lever the fulcrum is again at the end, but the effort is in the middle Think of a pair of tweezers
WEDGE A wedge: Two inclined planes joined back to back.
WEDGE Wedges are used to split things.
WHEEL AND AXLE The wheel and axle is a simple machine The axle is a rod that goes through the wheel which allows the wheel to turn Gears are a form of wheels and axles
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. In reverse, a short powerful force at the axle will move the wheel's edge a greater distance.
INCLINED PLANE An inclined plane is a slanting surface connecting a lower level to a higher level.
INCLINED PLANE An inclined plane is a flat surface that is higher on one end Inclined planes make the work of moving things easier
SCREWS A screw is an inclined plane wrapped around a shaft or cylinder. The inclined plane allows the screw to move itself when rotated.
SCREWS A screw is an inclined plane wrapped around a pole which holds things together or lifts materials.
COMPLEX MACHINES
Two or more simple machines working together to make work easier Two or more simple machines working together to make work easier. Examples: Wheelbarrow, Can Opener, Bicycle
VIDEO https://www.youtube.com/watch?v=4JWi2tkplYs
Web sites http://legacy.mos.org/sln/Leonardo/InventorsToolbox.html http://www.engquest.org.au/students-sm-up.cfm#Screws?CFID=1231605&CFTOKEN=49727120 http://www.mikids.com/Smachines.htm