Presentation on theme: "A machine is an invention that makes work easier."— Presentation transcript:
1A machine is an invention that makes work easier. Simple MachinesA machine is an invention that makes work easier.Remember that Work = Force x Distance A simple machine changes: the strength of a push or a pull force or the distance of a movement, to complete a task more easily. This produces a MECHANICAL ADVANTAGE
2The Six Simple Machines PULLEYA circular lever that consists of a grooved wheel rotating about a hubThe Six Simple MachinesDID YOU KNOW? All simple machines are derived from either the inclined plane or the lever.WEDGETwo inclined planes placed back to backINCLINED PLANEAny slanting flat surfaceSCREWAn inclined plane wrapped around a cylinderLEVERA rigid bar that rotates on a pivot called a fulcrum1st ClassFulcrum in middle2nd ClassLoad in middle3rd ClassEffort in middleWHEEL & AXLEA fixed wheel turning on a rod through its center
3Inclined PlaneAn inclined plane or ramp is one of the simplest machines. An inclined plane is a slanting surface connecting a lower level to a higher level. It is easier to push something up a gentle ramp than up a steep one.Force is decreased but distance is increased so work stays the sameDoes using an inclined plane decrease force or distance?
4Perhaps rollers gave an inventor the idea for the wheel! The great blocks of stone that made the pyramids weren't lifted into place they were rolled up ramps, or what we now call inclined planes. The inclined plane, one of the simple machines, allows you to raise great weights with small forces.Perhaps rollers gave an inventor the idea for the wheel!We’ll talk more about wheels later!
5How does a wedge increase force? Hint: Look at yellow diagram. Wedges are really a kind of inclined plane, but they are so useful that people give them their own category. A wedge is two inclined planes aligned back to back which ends in a sharp edge and separates material.When the force is applied downward on a wedge, it is able to push outward in two directions.How does a wedge increase force? Hint: Look at yellow diagram.
6What could this little bear change in order to lift the bigger bear? LeversA lever is a simple machine made with a rigid arm or a bar. It has a fixed pivot or fulcrum where it turns. If you add a push or pull force (effort) on one end of a see-saw, the other end goes in the opposite direction. The resisting weight is called the load. A light person can balance a heavier person on a see-saw. The lighter person must sit further from the pivot.If she moves the fulcrum closer to the load she will need less force to lift it.What could this little bear change in order to lift the bigger bear?
7Three Classes of Levers Fulcrum in middleLoad in middleEffort in middleThree Classes of Levers
8Wheel and AxleThe wheel and axle is generally considered to be a circular lever, disk-shaped object with a hole in the center. This “wheel” is attached to a cylindrical rod called an axle. These two parts rotate together so that force is transferred from one to the other. The wheels turn around the axle, which is attached to some type of vehicle.Did You Know? Gears are wheels with teeth that can be used to gain force or speed or change direction.The invention of the wheel is one of the most important in the history of man, similar in importance to the discovery of fire and the development of writing, and electricity.The force applied to the axle is increasedWhat changes when the force transfers from wheel to axle?The wheel goes a further distance with the same forceWhat changes when the force transfers from axle to wheel?
9PulleysA pulley is another special kind of wheel. It has a groove on the outside for a string or rope. You can raise a flag up a pole with a simple pulley. When you pull down on the rope, the pulley turns and the flag goes up.Did You Know? A fixed pulley is fastened to one spot, and does not move around. It provides no gain in force, distance or speed, but it changes the direction of the forceMaking work easier With two pulleys you canlift twice as much weightwith the same effort. Withmore pulleys you can lifteven heavier loads.By adding more ropes to share the loadHow does a pulley produce a mechanical advantage?
10How is a screw like a wedge? ScrewsA screw is an inclined plane wrapped around a cylinder. It holds things together or lifts materials. It has a groove called a thread which winds around a spiral shape. When you turn a wood screw the thread cuts into the wood. With each turn the screw is pulled into the wood by one thickness of the thread.You can’t push a screw into wood with your bare hands. The screw thread multiplies your strength by winding the screw in, a little at a time.How a screw worksScrews multiply effort. Allthe effort to turn them isconcentrated into a smallmovement inwards. Thisproduces a very large force.It increases the forceHow is a screw like a wedge?
11Checking Understanding 1. This is an example of: a) Inclined Plane b) Pulley c) Screw d) Lever
12Checking Understanding 2. Which of the following statement is true? a) b is the fulcrum, c is the resistance, a is the effort b) b is the resistance, c is the fulcrum, a is the effort c)b is the fulcrum, a is the effort, c is the resistance. d) b is the resistance, a is the fulcrum, c is the effort
13Checking Understanding 3. A simple machine that is actually a kind of inclined plane is a a) pulley b) wedge c) gear d) balance
14Checking Understanding 4. Decreasing the slant of an inclined plane increases its. a) effort force b) Mechanical Advantage b) Power d) Work output
15Checking Understanding 5. A screw is an example of a (an)a) Inclined Plane b) Wedge c) ramp d)pulley
16Checking Understanding 6. A pulley is an example of a (an)a) Inclined Plane b) Wheel c) ramp d)pulley
17Checking Understanding 7. When you turn the screw it moves forward(a) with a smaller force(b) with the same force(c) by a greater distance(d) with a greater force