Simple Machines Chapter Notes | Physics Class 6 ICSE PDF Download

Introduction

In this chapter, we will learn about simple machines, which are tools that help us do work easily. We use them every day to lift heavy things, move objects, or do tasks with less effort. Simple machines make our work faster and simpler by changing the force we apply. We will also study about work and energy, which are important to understand how machines help us. There are six types of simple machines, and we will explore each one in detail, like levers, inclined planes, and pulleys, along with how they work and their advantages.

Work and Energy

Work

• Work means applying force to move an object or change its shape or position.
• In science, work happens when a force moves an object in the direction of the force.
• Examples where work is done:
  • A boy lifting his school bag from the ground.
  • A girl riding a bicycle.
  • Girls playing hockey.
  • A man pushing a pram.
• No work is done if the object does not move, even if force is applied.
• Examples where no work is done:
  • A child standing with his bag, waiting for the school bus.
  • A person pushing a tree that does not move.

Did You Know?

James Prescott Joule (1818-1889) was an English physicist. He studied heat and its connection to mechanical work. He discovered the law of conservation of energy. This law deals with the first law of thermodynamics. He also worked on how energy transfers. The unit of energy, joule (J), is named after James Joule.

Energy

• Work and energy are closely related.
• We use energy to do work every day.
• Energy helps us wake up, take a bath, go to school, study, and play.
• When we play or work for a long time, we feel tired.
• We feel tired because our body uses up energy to do work.
• Energy is the cause, and work is the effect.

Simple Machines

A machine is an object that helps us do a task with less effort.

• Simple machines are basic tools we use every day.
  • Examples of simple machines: scissors, doorknobs, bottle openers, pencil sharpeners, hammers, board pins, sewing needles.
• Complex machinesare made by combining two or more simple machines.
  • Example of a complex machine: a bicycle has wheels, levers, and pulleys.

Mechanical Advantage

• A simple machine works by applying force on its own.
• Force applied on the machine to do work is called effort (E).
• The force exerted by the machine is called the load (L).
• Mechanical advantage (M.A.) is a number that tells how much a machine helps us.
• Formula for mechanical advantage:
  
• M.A. can be greater than 1, equal to 1, or less than 1.
• If M.A. > 1, the machine is a force multiplier (load is greater than effort).
• If M.A. < 1, the machine is a speed multiplier (load is less than effort).
• If M.A. = 1, the load is equal to the effort.
• The higher the M.A., the less effort we need to apply.

Types of Simple Machines

There are six types of simple machines: lever, inclined plane, pulley, screw, wheel and axle, and wedge.
We will study them in detail:

Lever

• A lever is a rigid bar or rod that moves around a fixed point called the fulcrum.
• A lever is used to lift heavy weights with less effort.
• Example: A person uses a rod to move a big stone by keeping a small stone as a fulcrum.
• The point where effort is applied is called the effort arm.
• The point where the load is lifted is called the load arm.
• Formula for a lever:
  
• If effort arm is greater than load arm, M.A. is greater than 1.
• If effort arm is less than load arm, M.A. is less than 1.
• If effort arm is equal to load arm, M.A. is equal to 1.
• Examples of levers in daily life: hammer, tongs, scissors, pliers, nail clippers.
• Levers are divided into three classes: Class I lever, Class II lever, and Class III lever.

Class I Lever

• In a Class I lever, the fulcrum is between the effort and the load.
• A Class I lever changes the direction of force.
  • Example: Applying a downward force (effort) on the lever moves the load upward.
• The M.A. of a Class I lever can be greater than 1, equal to 1, or less than 1.
  • Examples: scissors, pliers, crowbar, oar of a rowing boat, see-saw.

Class II Lever

• In a Class II lever, the load is between the fulcrum and the effort.
• The effort arm is always longer than the load arm.
• The M.A. of a Class II lever is always greater than 1, so it is a force multiplier.
  • Examples: bottle opener, wheelbarrow, nutcracker.

Class III Lever

• In a Class III lever, the effort is between the fulcrum and the load.
• The effort arm is smaller than the load arm.
• The M.A. of a Class III lever is less than 1, so it is a speed multiplier.
• The distance moved by the load is greater than the distance moved by the effort.
  • Examples: tongs, fishing rod, knife, broom.

Inclined Plane

• An inclined plane is a sloping surface that connects two points at different heights.
• It helps move heavy objects up or down with less effort.
  • Example: At construction sites, workers use an inclined plane to push heavy loads up.
• The force is applied only while pushing the load.
• The longer the inclined plane, the easier it is to move the load, but it takes more time.
• The steeper the slope, the more effort is needed to push the load.
• Formula for mechanical advantage of an inclined plane:
  
• If M.A. is greater than 1, the effort needed to lift a load is less than the load.
• An inclined plane acts as a force multiplier.
  • Examples: children’s slide, ramps for wheelchairs, sloping roads.
• In hospitals, schools, and offices, inclined planes are used as ramps for handicapped people or those in wheelchairs.

Pulley

• A pulley is a simple machine with a wheel and a groove on its rim where a rope or chain runs.
• The wheel is mounted on an axle and fitted in a frame called a block.
• The wheel is free to rotate.
• A pulley is used to lift heavy objects by changing the direction of force.
• The load is at one end of the rope, and effort is applied at the other end.
  • Examples: drawing water from a well, raising a flag on a flagpole.
• Multiple pulleys together reduce the force needed to lift heavy loads.
• An arrangement of pulleys is called a block and tackle system.

Pulleys Are of Two Main Types:

1. Fixed pulley:
   • In a fixed pulley, the pulley is attached to a hook or wall.
   • It does not move but changes the direction of force.
   • Examples: well pulley, flagpole pulley.
   • The M.A. of a fixed pulley is equal to 1.
   • The applied force is equal to the weight of the load.
2. Movable pulley:
   • A movable pulley moves with the load.
   • It reduces the effort needed to pull the load.
   • The M.A. of a movable pulley is less than the weight of the load.
   • Examples: cranes, block and tackle systems in sailing boats.

Screw

• A screw is a simple machine that looks like an inclined plane wrapped around a rod.
• It has spiral threads on it, which help it hold things together or lift heavy objects.
• The threads of a screw are very important because they grip the material tightly.
• The distance between two threads on a screw is called its lead.
• The lead decides how strong the screw is and how much advantage it gives.
• If the lead is small, the screw gives more mechanical advantage.
• A screw can be used to hold pieces of wood or other materials together.
• It takes less effort to put a screw in wood than to hammer a nail into it.
• A screw is also used as a force multiplier, meaning it makes work easier.
• Examples of screws are bolts, screws, screw caps of jars, and bottle caps.
• A screw jack is a tool that uses a screw to lift heavy things, like a car.

Wheel and Axle

• A wheel and axle is a simple machine made of a wheel attached to a rod called an axle.
• The wheel and axle must move together to work properly.
• It helps us do work with less effort by acting as a force multiplier or speed multiplier.
• A force multiplier means it helps us move heavy objects with less force.
• A speed multiplier means it makes things move faster, like in a bicycle or car tyres.
• Examples of wheel and axle are doorknobs, steering wheels, and bicycle wheels.
• In a doorknob, the wheel is the knob, and the axle is the rod inside it.
• In a steering wheel of a car, the wheel moves the axle to turn the car easily.
• In a bicycle, turning the axle makes the wheel spin faster to move quickly.
• The mechanical advantage of a wheel and axle depends on the size of the wheel and axle.
• Mechanical advantage is the ratio of the radius of the wheel to the radius of the axle.
• If the wheel is bigger than the axle, it gives more mechanical advantage.

Wedge

• A wedge is a simple machine made of wood or metal with two slanting sides.
• The slanting sides meet at a sharp or pointed edge.
• A wedge is usually made of two inclined planes joined together.
• It is used to split, cut, or hold objects tightly.
• Examples of wedges are blades, knives, door stoppers, axes, and ploughs.
• When we use a wedge, the sharp edge cuts or splits the object easily.
• The sharp edge of a wedge has a small surface area, so it puts more pressure on the object.
• This makes it easier to cut or split things, like cutting a log of wood with an axe.

Functioning of Simple Machines

Simple machines are tools or devices that simplify tasks and speed up work by assisting us in various ways:

• By altering the direction of applied force for better suitability: A pulley, for instance, simplifies work by changing the force's direction. For example, lifting a bucket of water straight up from a well is challenging, but a pulley allows us to pull downward to easily draw the water.
• By applying force at an optimal position: A lever simplifies work by letting us apply force at a strategic point. For instance, we can use one side of a pair of pliers to exert force and bend or compress an object on the other side.
• By amplifying the applied force: A screw jack increases the force applied, making it easier to lift heavy loads, such as a car, with minimal effort.
• By enhancing the speed of an object: A wheel and axle system acts as a speed multiplier in a car. Force is applied to the axle (smaller wheel), which rotates a short distance, while the wheel (larger wheel) covers a greater distance in the same time, allowing the car to move faster.

Efficiency of a Machine

• We know that a machine makes tasks easier for us, but it does not create energy.
• A machine uses the energy we give it to do work.
• The work we put into the machine is called input work.
• The work the machine does for us is called output work.
• The ratio of output work to input work is called the efficiency of the machine.
• Efficiency is written as a percentage (%).
  
• No machine has 100% efficiency because some energy is always lost as heat due to friction between parts.
  
• For example, if a machine has 90% efficiency, it means 90% of the input work becomes useful output, and 10% is lost as heat.
• A machine with 100% efficiency is called an ideal machine, but this is not possible in real life.
• In nature, petrol engines have about 50% efficiency, and diesel engines have about 40% efficiency.
• This means only 50% of petrol energy or 40% of diesel energy turns into useful work, and the rest is lost.

Care of Machines

We must take care of machines so they work well for a long time. Here are some ways to care for machines:

• Keep machines covered when not in use to protect them from dust and moisture.
• Store machines in clean places away from dirt and moisture to stop rusting.
• We can also paint machines to protect them from moisture.
• Put oil or grease on machine parts regularly to reduce friction.
• Reducing friction helps the machine work better and last longer.

Points To Remember

• Energy is the cause of work, and work is the effect of energy.
• Machines can be simple or complex.
• Simple machines can change the direction of force in the most suitable way.
• Simple machines help us do work by applying force at a convenient position or increasing the speed of the object.
• A simple machine does not produce energy on its own; it uses the energy we give it.
• If the mechanical advantage is more than 1, it means the load is more than the effort, and we say the machine is a force multiplier.
• The more the mechanical advantage, the less effort we need to apply.
• There are six types of simple machines: lever, inclined plane, pulley, screw, wheel and axle, and wedge.
• A lever is used to lift heavy weights with a small amount of effort.
• For a lever, mechanical advantage = load / effort or effort arm / load arm.
• There are three classes of levers: class I lever, class II lever, and class III lever.
• In class I lever, the fulcrum (fixed point) is between the effort and the load.
• In class II lever, the load is between the fulcrum and the effort.
• In class III lever, the effort is between the fulcrum and the load.
• An inclined plane reduces the effort needed to lift objects.
• For an inclined plane, mechanical advantage = length of the inclined plane / vertical height.
• Pulleys help in lifting heavy loads.
• Pulleys are of two types: fixed pulley and movable pulley.
• In a fixed pulley, the pulley is attached to a hook or wall and does not move.
• In a movable pulley, the effort is reduced, and the pulley moves with the load.
• The smaller the lead of a screw, the higher the mechanical advantage.
• A screw is a force multiplier, meaning it helps lift heavy objects with less effort.
• A wheel and axle can act as a force multiplier or a speed multiplier.
• A wedge is a combination of two inclined planes.
• Efficiency of a machine tells us how much input energy is converted to useful output energy.
• In an ideal machine, the total output energy is equal to the total input energy.
• We should take care of machines so they work well for a long time.

​Glossary

• Work: When a force moves an object or changes its position or shape.
• Energy: The ability of a body to do work.
• Machine: An object that helps us do work with less effort.
• Simple machines: Basic devices we use in daily life that are made of one or two parts.
• Complex machines: Machines that are made by combining two or more simple machines.
• Effort: The force we apply on a machine to do work.
• Load: The object or weight that the machine moves or lifts.
• Mechanical advantage: The ratio of the load lifted by a machine to the effort applied to it.
• Lever: A rigid bar that can move around a fixed point to lift or move objects.
• Inclined plane: A slanting surface that connects two points at different heights to move objects up or down easily.
• Pulley: A simple machine with a wheel and a rope or chain to lift heavy objects.
• Screw: An inclined plane wrapped around a rod with spiral threads to hold or lift things.
• Wheel and axle: A wheel attached to a rod or shaft that moves together to make work easier.
• Wedge: A simple machine with two slanting sides and a sharp edge to cut or split objects.
• Efficiency of a machine: The ratio of work done by a machine to the work we put into it.