Presentation on theme: "Simple Machines A machine is an invention that makes work easier. Remember that Work = Force x Distance A simple machine changes: the strength of a push."— Presentation transcript:
Simple Machines A 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
WEDGE Two inclined planes placed back to back INCLINED PLANE Any slanting flat surface PULLEY A circular lever that consists of a grooved wheel rotating about a hub SCREW An inclined plane wrapped around a cylinder WHEEL & AXLE A fixed wheel turning on a rod through its center LEVER A rigid bar that rotates on a pivot called a fulcrum 1 st Class Fulcrum in middle 2 nd Class Load in middle 3 rd Class Effort in middle The Six Simple Machines DID YOU KNOW? All simple machines are derived from either the inclined plane or the lever.
Inclined Plane An 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. Does using an inclined plane decrease force or distance? Force is decreased but distance is increased so work stays the same
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!
Wedge 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. How does a wedge increase force? Hint: Look at yellow diagram. When the force is applied downward on a wedge, it is able to push outward in two directions.
Levers A 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. What could this little bear change in order to lift the bigger bear? If she moves the fulcrum closer to the load she will need less force to lift it.
Fulcrum in middleLoad in middleEffort in middle Three Classes of Levers
Wheel and Axle The 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. 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. What changes when the force transfers from axle to wheel? Did You Know? Gears are wheels with teeth that can be used to gain force or speed or change direction. The wheel goes a further distance with the same force What changes when the force transfers from wheel to axle? The force applied to the axle is increased
Pulleys A 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. Making work easier With two pulleys you can lift twice as much weight with the same effort. With more pulleys you can lift even heavier loads. How does a pulley produce a mechanical advantage? 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 force By adding more ropes to share the load
Screws A 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 works Screws multiply effort. All the effort to turn them is concentrated into a small movement inwards. This produces a very large force. How is a screw like a wedge?It increases the force
1. This is an example of: a) Inclined Plane b) Pulley c) Screw d) Lever
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
3. A simple machine that is actually a kind of inclined plane is a a) pulley b) wedge c) gear d) balance
4. Decreasing the slant of an inclined plane increases its. a) effort force b) Mechanical Advantage b) Power d) Work output
5. A screw is an example of a (an) a) Inclined Plane b) Wedge c) ramp d)pulley
6. A pulley is an example of a (an) a) Inclined Plane b) Wheel c) ramp d)pulley
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