# 5th Class Science Work, Force and Energy Work, Force Energy and Machines

## Work, Force Energy and Machines

Category : 5th Class

LEARNING OBJECTIVES

• Learn about the basic concepts of work and force.
• Study about the role of energy in doing work.
• Study and learn about various machines that are used for doing some work.
• Study about the mechanism of working of machines.

QUICK CONCEPT REVIEW

WORK

Work is done only when an object moves over distance on applying force.

Example:  If you move a pencil, work is done, but after applying lots of force, if you are not able to move a pencil, no work is done.

Force

Force is needed to pull or push something. You cannot move an object without using force. For example: you cannot push a ball without using force. To move a light object like pencil, you will have to use less force and to move a heavy object like a table; you have to apply more fore. Force can slow, stop or change the direction of a moving object.

Push: An act of exerting force on someone or something to move them away from oneself.

Pull: An act of taking hold of something and exerting force to draw it towards oneself.

There are various types of forces that are either exhibited by or on a body.

Real-Life Example

• When we want to put a wall hanging we use a simple machine ‘nail’ or ‘screw’ and drill it into the wall using a complex drilling machine.

Misconcept/concept

Misconnect: Friction force is considered as the negative work.

Concept: Work done can never be negative. Friction force slows down the sliding motion and thus is very crucial in day to day activities.

Misconnect:  An object at rest has no energy.

Concept:  The object at rest has potential energy. As the object starts moving, its potential energy converts into kinetic energy and then into other energies.

Types of Forces

Friction Force: Friction is resistance of solid surfaces, layers and material elements. Gravity: The force that attracts a body towards the centre of the earth or towards any other physical body having mass is called gravity.

Buoyant Force: Buoyancy is the upward force on an object produced by the surrounding liquid or gas in which it is fully or partially immersed, due to the pressure difference of the fluid between the top and bottom of the object.

This force enables the object to float or at least seem lighter.

Buoyancy is important for many vehicles such as boats, ships, balloons, and airships.

Magnetic Force: When two magnets come together or push away from each other, they exhibit magnetic force.

Applied Force: It is a force that is applied to an object by a person or another object.

ENERGY

Energy is the ability to do work. When you apply force on an object, your uses energy. Energy can be neither created nor destroyed.

Example: to move a table, you   apply force and to do so your body uses energy. Your body produces energy from the food you eat. A moving car uses energy from the fuel it burns. Whenever force is applied, energy is used.

SOURCES OF ENERGY

We use energy from different sources in our day to day life.

1. Food: Your body gets energy from the food you eat.
2. Electrical energy: It is used to operate fans, things in homes and factories.
3. Burning wood, coal and Liquefied Petroleum Gas, (LPG); It is used to cook food.
4. Soar energy: It is used for heating and lighting. Plants use sunlight to make food.
5. Petrol and Diesel: It is used to run cars, trucks and airplanes.
6. Wind energy: It is used to work pumps in agricultural fields.

TYPES OF ENERGY

• Energy can be of many different types. Some are renewable energy whereas others are non-renewable energy.
• One form of energy can be transferred to another form of energy.
• Solar energy is the most important source of energy. Every other energy is derived from solar energy.
• When a body is kept at rest and is not undergoing any work, then the energy in the body is called potential energy.
• When a body is in motion and is doing work, it is exhibiting kinetic energy.

MACHINES

Machines are used to make certain tasks easy. Machines like bicycle, sewing machine, etc., are made up of many ports. They are called complex machines. Some machines are very simple. Like any other machine, a simple machine helps us to perform certain tasks with ease.

Example: Needle, knife, etc.

Simple machines: Simple machines are able to increase a force when energy is added to them. This means that they make work easier. Simple machines can also change the direction of the force or make things move faster. Examples of classic simple machines are:

1. Lever
2. Wheel and axle: The wheel and axel is a simple machine. The axle will turn when there is force on the wheel. A car, wagon, and roller skates are examples of a wheel and axle. A wheel and axle moves things place to place.
3. Pulley: A pulley is a machine made up of a wheel and rope. Some examples of pulleys are flog poles, sail boats, and cranes. Pulleys let you move objects up and down.
4. Inclined plane: An inclined plane is a flat surface that is higher on one end. Some examples of an inclined plane are door stops, bike romps, and slides. Inclined planes help us move things to low or higher places.
5. Wedge: A wedge is a simple machine also. A wedge pushes two things apart. Some examples are knives, forks, and nails. A wedge is made up of two inclined planes.
6. Screw: A screw is an inclined plane wrapped around a rod. Some examples of a screw are clamps, spiral stair cases, and wrenches. Screws hold things together.

COHPLEX MACHINES

A complex machine is a machine that is made up of more than one simple machine. The simple machines work together to make work easier. Cars and bicycles are examples of complex machines.

Amazing Facts

• Approximately 30% of energy used in buildings is used inefficiently or unnecessarily.
• America burns nearly half of the world’s petrol.
• If a person yelled for 8 years, 7 months and 6 days, he or she would produce enough energy to heat one cup of coffee.
• The force of gravity 100 kilometers (62 miles) above Earth is just 3% less than at the Earth’s surface.
• Tides are caused by the rotation of the Earth and the gravitational effects of the Moon and Sun.

Historical Preview

• The idea of a ‘’simple machine’’ originated with the Greek philosopher Archimedes around the 3rd century BC, who studied the ‘’Archimedean’’ simple machines: lever, pulley, and screw.

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