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(a) Fulcrum, load and effort

(b) Load, fulcrum, effort

(c) Effort, fulcrum, load

A pulley is a wheel or a circular disc that can rotate freely about its axle. It is used to lift heavy objects. It is neither a force multiplier nor a speed multiplier. It only changes the direction of the applied force from upwards against gravity to downwards towards gravity. 

There are two types of pulley systems – Single fixed pulley and single movable pulley.

(1) easily

(2) complicated

(3) slope, weight, longer

(4) slope, shorter, greater

(5) iron

(6) breaking, separate

(7) crow-bar

(8) pulley

(9) upward

(10) simple

(11) wedge

(12) dust

(13) 45°, water, flat surface.

A slanting plank which is used to lift a weight on which we bear less weight and lifting becomes easier is an inclined plane.

1. Mixer grinder – To grind the foodstuffs

2. Scooter – To ride and reach places

3. Bicycle – To ride and reach places

4. Sewing machine – To stitch clothes

5. Wheel chair – Specially designed for handicapped patients to move around.

Properties of complex machine are :

1. These machines have many parts to carry out many processes. 

2. The parts are joined to one another. 

3. The structure of complex machines is complicated. 

4. Some parts of complex machines are actually simple machines.

Mechanical advantage: The ratio between load and effort is called mechanical advantage (M.A.): 

M.A. = Load(L)/Effort(E)

It has no unit. Velocity ratio: The ratio between displacement of effort and displacement of load is called

Velocity ratio (V.R.): V. R. = d_E/d_L

Where d_E and d_L are the displacement of effort and load respectively in time t. 

 Levers of II order: 

(i) Lock and key 

(ii) Opener of soda water bottle 

(iii) Closing a door

Machines help us to perform the same amount of work with much less effort than if we did the work manually. They also make our work faster and easier by multiplying the speed or the force applied.

 Nut cracker and Hand Pump. 

The force applied on the other end of the rod to lift the load is called an effort.

Efficiency of a machine is always less than 100% as output energy is always less than the input energy, because some energy is lost to overcome friction.

The principle of a lever is derived from the principle of moments. It states that “The moments of the load about the fulcrum is equal to the moments of the effort about the effort arm”, i.e.,

Load x load arm = Effort x Effort arm.

M.A. of a lever = Load/Effort = (Effort arm)/(Load arm). 

Levers of 1st order: 

(i) Railway signal 

(ii) Handle of water pump 

(iii) Motor car foot brake 

(iv) Nail cutter

Class III lever (hockey stick, fbreep)

The mechanical advantage of class II levers is always more- than 1. 

Example – Nut cracker, wheel barrow, bottle opener etc.

Mechanical advantage of a lever = (Effort arm)/(Load arm)

The part of the lever from the fulcrum to the effort is called an effort arm.

Class IInd levers has mechanical advantage always greater than one. To increase the mechanical advantage of class II length of effort arm must be increased and distance between fulcrum and load should be decreased.

Efficiency of a machine is always less than 100% as output energy is always less than the input energy, because some energy is lost to overcome friction.

The efficiency of an ideal machine is 1 (or 100%).

Various functions that a machine can perform are : 

1. Changing the direction of applied force — Example : When a flag is hoisted with the help of a pulley. 

2. Changing the magnitude of applied force —- Example : Bottle opener multiplies the applied force and much less effort is required to open the cap. 

3. Applying force at a convenient point — Example : hi a pair of scissors, the input force is applied at the handle of the scissors which cuts the paper at the other end of the blade. 

4. Changing the speed of an object — Example : While riding a bicycle, force is applied on pedals which multiplies the speed.

The load is in the centre, the fulcrum on one side, and the effort on the other side.

The mechanical advantage of second order lever is always more than 1. This is because the effort arm is always longer than the load arm of these levers. 

The effort is in the centre, the fulcrum on one side, and the load on the other side.

The fulcrum is in the centre, the load is at one end while effort is at other end.

A lever is a machine made up of 3 parts : 

Effort, load and fulcrum.

1. more than 1: Load arm of pliers 

2. equal to 1: See – saw 

3. less than 1: The load arm of a pair of scissors.

It is used only to change the direction of effort to a more convenient direction and to use one’s own weight for the effort.

3. equalto unity

Mechanical advantage (MA) = Lord / Effort

(a) A pair of scissors — Class I lever 

(b) a lemon squeezer — Class II lever 

(c) a nut cracker — Class II lever 

(d) a pair of sugar tongs — Class III lever 

(e) a beam balance — Class I lever 

(f) an oar rowing a boat — Class I lever 

(g) a wheel barrow — Class II lever 

(h) a see saw — Class I lever 

(i) a pair of pilers — Class I lever 

(j) a crow bar — Class I lever

Task such as using a nut cracker, cutting paper with scissors, can be done using a lever.

2. Load / Effort

3. helps to apply the force in a convenient direction

1. False. 

There are six types of simple machines.

2. False. 

The load and effort cannot act at a single point in a lever.

3. True

4. True

5. False. 

A single fixed pulley is a pulley that has its axis of rotation fixed.

6. True

7. True

8. False. 

Work done by a machine is always less than the work done on a machine.

3. Class III

A pair of scissors is an example of a/an 

2. lever 

4. Load ann — Effort arm

3. A nut-cracker

The effort required to lift a load of 800 N by using a lever having a mechanical advantage of 1.6 is 

4. 500 N

1. Needle and thread – Stitching of clothes 

2. Wheelbarrow – To carry materials. 

3. Opener – To open the lids of bottles. 

4. Pulley – To lift bucket 

5. Nail cutter – To cut nails 

6. Axe – To cut wood into small pieces

We can reach the mountain top by climbing the pathway early than by the road. The time required is less but the strength required is more. The road is easy to walk and more time consuming.

A machine does some useful work when energy is supplied to it. Energy supplied to machine (or input) = Effort × Displacement of the point of application of effort. Work obtained from machine (or output)= Load × Displacement of the point of application of load. For an ideal machine, Work output = Work input.