☆ simple machines:
● Machine is a device which help us by acting as a force multiplier or Speed multiplier allowing us to apply effort at a more convenient point in an easier direction.
● The simple tools such as spoon, a wrench, a bottle opener, a trolley, a crow bar, a needle, a pair of scissors, door knob, a pulley, a screw driver etc., are some of the examples to show that a machine makes a difficult work easy. These are called as simple machines.
•A machine using several moving parts run by an engine or electricity is called as complex machines. Such complicated machines are generally used in factories.
● some examples of simple machines are:
1. Opening the lid of tin container using a spoon.
2. Spanner which is used to open a tight nut.
3. Opening a tightly fitted cork from a bottle using a screw driver.
4. A boy carrying a heavy load on a trolley.
5. A crane is used to lift heavy equipments.
6.A bottle opener is used to open the lid of a soft drink bottle.
7.A needle is used for sewing and a pair of scissors for cutting the cloth.
8. A door knob is used to lock and unlock the door.
9. A pulley is used to pull a a bucket of water from a well.
10. An iron bar is used to lift a heavy stone by pushing it.
☆ work and energy:
● work
- work is said to be done if the force applied on the body moves it. If no motion all change in position takes place, no work is said to be done.
● The SI unit of work is Joule.
● Its symbol is J.
● work is a scalar quantity.
● work= force× displacement
or
Work= force× distance moved by the body in the direction of force.
● SI unit of work= SI unit of force× S.I . unit of displacement
=N×m
=J
☆ Energy:
- the the energy of a body is its capacity or ability to do work.
● SI unit of energy is Joule.
● symbol is J.
●It is a scalar quantity.
☆ principle of a machine:
- No machine works by itself.
● To do work on a machine, a force is applied called as effort. Its Symbol is E.
● The machine exert a force to do work, this force exerted by the machine is called load. Its Symbol is L .
☆ Efficiency of a machine:
- The efficiency of a machine is the ratio of the useful work done by the machine to the work put into the machine by the effort.
● Efficiency= useful work done by the machine on the load / work done on the machine by the effort
Or
Efficiency= work output on load / work input by effort.
☆ ideal or perfect machine:
- a machine in which no part of the work done on the machine is wasted is called an ideal or perfect machine.
● for an ideal machine, the work output is equal to work input.
● the efficiency of an ideal machine is 1or hundred percent.
● actual machine:
- no machine is perfect because some part of the work done on a machine is always used up or wasted in overcoming the friction between the moving parts of the machine.
- the work output of a machine is always less than the work input.
● if a machine is 75% efficient it means that 75% of the work input to the machine is obtained as the useful work output and the remaining 25% of the work input has been wasted in overcoming the friction.
☆ functions of a simple machine:
● it decreases the magnitude of the force required, i.e., effort is less than the load. Acts as a force multiplier.
Example jack used to lift a car,a bar,a spade etc.,
● it increases the distance moved by the load. Acts as a speed multiplier.
Example a pair of Scissors its arms move longer on cloth then its handle while in use.
● it changes the direction of effort in a convenient direction. Acts as a direction changer
. Example Pulley.
● it changes the point of application of effort to a convenient point. Help us to apply effort at a more convenient point.
Example in a bicycle the rear wheel is jointed with the help of a chain to a toothed wheel attached with Pedal the rear wheel is rotated by applying the effort on the pedal.
● simple machine are of following six types :
1.Lever:
- A Lever is a rigid ,straight or bent bar which is capable of turning about a fixed turning point called fulcrum.
- It may act as a force multiplier or speed multiplier .
2. The pulley.
3. The wheel and axle.eg door knob ,steering wheel etc.,
4. The incline plane. Staircase,ramp etc.,
5.The Wedge eg.,Needle,axe etc.
6.The screw.
☆ mechanical advantage:
● The mechanical advantage of a machine is the ratio of the load to the effort.
● mechanical advantage= load(L) / effort(E).
●MA > 1,The machine is called force multiplier
●MA<1, The machine is called speed multiplier.
●MA=1, the machine may act as a direction changer.
• The factor by which a machine multiplies the force applied is called the mechanical advantage of that machine.
●Tells us that how many times our effort gets multiplied.
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