Short notes-2 of chapter -4 based on simple machines of class 6

 ☆Levers:

-  A lever is a rigid straight or bent bar which is capable of turning about a fixed turning point called fulcrum.

* Principle of a lever-

According to principle of a lever,

Load×load Arm =effort×effort arm.

MA=load (L) / effort (E)

MA=effort arm / load arm.

•if load arm is greater than the effort arm , mechanical advantage is less than 1. It acts as a speed multiplier.

•if load arm is equal to the effort arm, the mechanical advantage is equal to 1. It acts as a direction changer or to apply effort at a more convenient point.

•if load arm  is smaller than the effort arm mechanical advantage is greater than 1. It acts as a force multiplier.

*Classes or orders of levers:

•depending upon the relative position of the fulcrum ,effort and load .levers are of three types-

  1. Levers of class 1-

  •The levers in which the fulcrum is in between the load and the effort are called the levers of class 1.

•The load and the effort both are in the same direction.

 •The effort arm of levers of class 1 is longer than the load arm.mechanical advantage of class 1 lever is  greater than 1.

•If the effort arm is equal to the load arm then mechanical advantage is equal to 1.

•If the effort arm is shorter than the load arm, its mechanical advantage is less than 1.

•The examples of class 1 levers are as follows:

 1.see-saw

 2. Pair of scissors,MA<1.

 3. A pair of pliers, MA>1.

 4. Beam balance,MA=1.

  5. A crowbar.

  6. Claw hammer

 7. Spoon opening the lid of a tin can.

 8. Handle of a hand pump

 9. The oar rowing a boat.

2. Levers of class 2-

-The levers in which the load is in between the fulcrum and the effort are called the levers of class 2.

•The load and the effort are in opposite directions.

 •Effort arm is always greater than the load arm.so ,the mechanical advantage of class 2 lever is always greater than 1. 

MA>1.

•Examples of class 2 lever are as follows:

1. Nut cracker

2. Wheel Barrow

3. Paper cutter

4. Mango cutter

5. Lemon squeezer

6. Bottle opener

3. Levers of class 3-

-The levers in which the effort is in between the fulcrum and the load are called the levers of class 3.

•The load and the effort are in opposite directions.

•The effort arm is always shorter than the load arm.so,the mechanical advantage of class 3 levers is always less than 1.

MA<1.

•Following are examples of class 3 levers:

1. Pair of tongs

2. Fore arm  holding a load

3. Sugar tongs

4. Forceps

5. Knife

6. Spade for lifting soil or coal.

Ways To increase the mechanical advantage of a Lever:

1. By increasing the effort or reducing the load arm.

2. Friction at the fulcrum reduces the mechanical advantage. So friction should be minimised.

☆ Pulley

● Pulley is a simple machine by which the direction of effort is changed to raise up a load.

-Pulley is grooved wheel which is free to rotate on an axle.

●MA= load/ effort.

●MA=1

● In an actual Pulley due to friction the mechanical advantage is always less than 1.

● The pulley allows us to apply the effort downwards that is in a convenient direction. One can hang on it to make use of his own weight also in order to apply the effort.

• Examples of pulley

1.Pulley is used for lifting a bucket full of water from a well .

2. For lifting a heavy material in a factory.

3. For lifting of a car engine in a garage

☆ wheel and axle-

• wheel and axle is is a simple machine which consists of either a wheel attached to an axle or two wheels of different diameters attached together .

• The effort is applied on the bigger wale and load is attached with a smaller wheel.

● It is used to provide the linear motion by the rotation of wheel and so it reduces the friction because rolling friction is less than the sliding friction.

• some examples of wheel and axle are as follows:

1. Steering wheel of a car

2. Bicycle pedal

3. Door knob

4. Screw Driver

5. Water tap

☆ incline plane:

● An incline plane is a simple machine with a slanting wooden plank or a sloping surface which is used to move a load up with a less effort.

● Mechanical advantage of an inclined plane is always greater than 1.

MA>1.

● Smaller the slope, more is the mechanical advantage.

• Larger the slope, lesser is the mechanical advantage.

• Following are the examples of an incline plane:

1. Incline plane used by Coolie to load the truck with drums.

2. A ramp Is provided in a building to move scooter, motorcycle or bicycle inside the building by pushing it along the ramp.

3. Hospital and huge buildings are provided with ramps which help nurses to move up the patients on a stretcher or to carrying heavy equipments.

4. The staircase in our house is also made as an inclined plane.

5. The roads on a hill are made incline with a small slope.

☆Wedge

●A wedge is a simple machine having Stark age which is formed by putting two inclined planes together.

● A wedge  is used to split a log of wood.

• Thicker the wedge, easier it is to drive the wedge into the log and split it into pieces.

● examples of a wedge are:

1. Knife

2.Axe

3. Plough

4.nail

5.saw

6.Needle

☆Screw

● A Screw is a simple machine which appears like an inclined plane wound around a rod with a pointed tip.

● The spiral groove formed on it are called the Threads of the screw.

• The one end of the rod is made narrow or pointed which is called the tip of the screw.

• Yhe other hand is made flat which is called the head of the screw.

• It is is driven into the wood by turning it with a screw driver because the screw then worked as an incline plane.so it is a modified form of an inclined plane.

☆ Care of Machines:

1. Which would keep the message clean and free from dust.

2. To prevent machine parts from rusting ,such parts must be painted from time to time.

3. To reduce friction in moving parts of a machine,it must be properly lubricated from time to time.