3What do these pictures tell you? What do they have in common?
4ACTIVITY Underline or find the following words in the following texts. ForceKickExertPushMove
5CONTACT FORCEEveryone 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.
8Once 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.
9A pulley is a simple machine that uses grooved wheels and a rope to raise, lower or move a load.
10Pulley 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
11LEVERA lever is a stiff bar that rests on a support called a fulcrum which lifts or moves loads.
12Levers-First ClassIn a first class lever the fulcrum is in the middle and the load and effort is on either sideThink of a see-saw
13Levers-Second ClassIn a second class lever the fulcrum is at the end, with the load in the middleThink of a wheelbarrow
14Levers-Third ClassIn a third class lever the fulcrum is again at the end, but the effort is in the middleThink of a pair of tweezers
15WEDGEA wedge: Two inclined planes joined back to back.
17WHEEL 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 turnGears are a form of wheels and axles
18Wheel and AxleIn 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.
19INCLINED PLANEAn inclined plane is a slanting surface connecting a lower level to a higher level.
20INCLINED PLANEAn inclined plane is a flat surface that is higher on one endInclined planes make the work of moving things easier
21SCREWSA screw is an inclined plane wrapped around a shaft or cylinder.The inclined plane allows the screw to move itself when rotated.
22SCREWSA screw is an inclined plane wrapped around a pole which holds things together or lifts materials.