IMPORTANT TERMS

Force                       A push or a pull acting on an object.

Friction                    The force that tries to stop the sliding movement of objects across a surface.

Energy                     The ability to do work.

Gravity                   The force that pulls everything towards the centre of the Earth.

Magnetism              The pull or push applied by a magnet on metals like iron and nickel.

Machine                   A tool that makes our work simpler and quicker.

Simple Machine      Uses a single applied force (effort) to overcome a single force (load).

Complex Machine   Consists of two or more simple machines working together.

FORCE

Force is required to change the status of an object. It can be used to move a stationary object but also used to stop a moving object. We cannot see force but we can see its effects. There are four different types of forces:-

Electrostatic Force: - It is a kind of force that pulls lighter objects towards itself once it is charged e.g. pieces of paper attracted towards a charged comb.

Frictional Force: - It is a kind of force, which tries to stop the movement of objects across a surface e.g. walking on the ground.

Gravitational Force: - It is kind of force that pulls everything towards the centre of the Earth e.g. a ball thrown up comes down due to gravity.

Magnetic force: - Push or pull applied by a magnet on metals like iron and nickel. e.g. game of dartboard.

ADVANTAGES OF FRICTION

• Friction between our feet and the ground makes it possible for us to walk. Friction helps us to apply force in backward direction and move our body forward.

• The friction between the tyres of vehicles and the road makes them roll forward. Thus, friction makes movement of vehicles possible.

• Writing with a pencil or a pen requires friction. We cannot hold a pencil without friction. Friction between the pencil and the paper makes it possible for a person to write. It also helps to erase pencil marks using an eraser.

DISADVANTAGES OF FRICTION

• Friction makes it hard to slide heavy objects such as a heavy piece of furniture across the floor.

• Friction causes damage to machine parts. Machines can get damaged if the friction is too strong. To reduce the damage, machine parts are oiled. Oiling causes slippery surface due to which the friction between various parts is reduced. This in turn causes lesser rubbing of parts against each other and lesser generation of heat thereby minimising the damage.

• It is difficult to walk on a wet floor because layer of water makes the floor smooth. The coating of water reduces the friction and the foot cannot make a proper grip on the floor, making it slippery.

ENERGY

The ability to do work is called energy. There are many forms of energy.

• Heat Energy: -It is a type of energy that is generated by burning of fuels like coal, LPG etc. We use this energy to cook food.
• Light Energy: - It is a type of energy which is used to see things around us. Tube light, lamp, bulb are some sources of light energy.
• Sound Energy: - It is a type of energy produced by many objects such as musical instruments and loud speakers.
• Wind Energy: - Power of the moving wind is utilized with the help of windmills to generate electrical energy.
• Mechanical Energy: - It is an energy that an object has due to its position or its movement.

• Electrical Energy: - It is generated at power stations and supplied to our homes. All the electrical appliances like television, computer and radio run with the use of electrical energy.

MACHINE

Machine may be a simple machine or a complex machine:

Simple machine: - A simple machine uses a single applied force to overcome a single force.  There are six types of simple machine:

Name of Machine		Types of machine	Mechanism	​Examples
Lever	A rigid rod that can move freely around a fixed point.   A sequence of load, fulcrum and effort   Class of a lever depends on relative positions of load, fulcrum and effort	First class lever	E-F-L	Scissor and See Saw
		Second class lever	E-L-F	Nut Cracker and Wheel Barrow
		Third class lever	L-E-F	Fishing rod and Stapler
Screw	An inclined plane spirally wrapped around a cylinder.			Screw in a door lock
Wedge	Has two inclined planes			An axe, a razor, a knife
Wheel and Axle	Large wheel connected to a small rod (axle).			Sewing machine, Steering of car
Inclined Plane	One end higher than the other; kind of slope			Ramps in hospitals
Pulley	Wheel with grooved rim for a rope or a chain to move.	Fixed Pulley	In a fixed pulley, axle is fixed to some kind of support like a hook or a wall.	Lift a bucket of water from well
		Movable pulley	The axle is not fixed to any kind of support.	A Crane machine

 

Complex machine: - A complex machine consists of two or more simple machines working together e.g. a car, an elevator.

INTERESTING FACTS

• Ancient Egyptians are known to be perhaps the first ones to use the principle of inclined planes when they used it to transport huge stones to build temples.

• Isaac Newton was the first scientist to propose the idea of gravity. An apple falling from a tree triggered his theory of gravitation.

• The lever is one of the basic tools. The lever has been used by man for thousands of years; probably in prehistoric times.

• Levers were first described by the ancient Greek mathematician Archimedes (287-212 BC).