Force and Simple Machines (Part 2) Class 5 Notes Science

Machines

Tools make our work easier by reducing the force that needs to be applied to get the work done. These tools are known as machines. 

• Machines help us to do work easily and with less effort. 
• Machines help us to do work in less time. 
• Machines make our life easy and comfortable. 

Machines may be simple or complex 

• Simple machines are tools that have very simple structure and that make our work easier and faster. 
• Complex machines consist of two or more simple machines that work together.

Types of Simple Machines

1. Lever

A lever consists of a rod free to move about a fixed point. It consists of three parts – fulcrum, load and effort.

• Fulcrum is the fixed point around which the lever moves. 
• Load is the object on which work is being done. 
• Effort is the force applied on the lever.

Depending on the position of the fulcrum, load, and effort, there are three types of levers.

• Class 1 Lever:  In class 1 levers, the fulcrum is between the load and the effort. A pair of scissors see-saw, crowbar and plier are examples of first-class levers.  

• Class 2 Lever: In class 2 levers, the load is between the fulcrum and effort. A bottle opener, a wheelbarrow, and a nut cracker are levers of class 2. A lever of class 2 always increases force.
• Class 3 Lever: In class 3 levers, the effort is between the fulcrum and load. Stapler, tweezers fishing rods and tongs are examples of third-class levers. This class of levers is used to decrease force to carry out delicate work. 

2. Wheel and Axle

• The wheel is one of the most important inventions by humans. 
• A wheel and axle consists of a wheel attached to a rod called an axle. 
• When the axle is turned, the wheel also moves. 
• The steering wheel of a car, screwdriver, sewing machine and doorknob are examples of wheel and axle.

There are two basic ways a wheel and axle can work together to help move things. 

• The force is applied to the wheel 
• The force is applied to the axle.

3.  Inclined Plane

• An inclined plane is simply a slope with one end higher than the other. 
• Less effort is needed to move an object up through an inclined plane as compared to lifting it up straight.
• A plank of wood is often used as an inclined plane to load heavy things on trucks.
•  An inclined plane makes it easier to push up a load.
• Ramp, staircase, slide and roads in hilly regions are examples of inclined planes.

4. Wedge

• When two inclined planes are joined back to back in the shape of V, it forms a wedge. 
• It can also be seen as an object with at least one slanting side ending in a sharp edge. 
• A nail, fork, knife and an axe are examples of wedge.

5. Screw

• A screw looks like a nail with grooves cut in it. 
• It has winding edge called thread. 
• To insert it into wood, it has to be screwed in by turning it round and round with a screwdriver.
• It helps to hold things tightly.  
• It takes less force to insert a screw in wood than a nail. 
• Therefore, a screw increases force.
• Screw jack, drilling machine and nut bolts are examples of screw.

6. Pulley

 A pulley is a wheel with a grooved rim so that a rope or chain can run around it. A pulley changes the direction of force applied. A pulley can be of two types – fixed pulley and movable pulley. 

• Fixed pulley: In a fixed pulley, the axle is fixed to a support. It is used for drawing water from a well and raising a flag to the top of a flagpole.

• Movable pulley: Movable pulley is used in combination with a fixed pulley. It is used to lift heavy loads.

Safety Habits While Using Simple Machines

Machines are helpful to us. However, they should be handled with care. 

• The moving parts of pulleys and levers can cause serious injuries. They should be used with care.
• Do not go near places where heavy loads are being lifted by pulleys. 
• Make sure that the rope is in good condition before using a pulley. The machines should be well lubricated.
• Sharp edges of knives, scissors axes are dangerous. Handle them with care.
• Never wave around your hand while using a pair of scissors. You could hurt someone around you. 
• When carrying sharp and pointed tools like knife, position the pointed edge downward.
• Hold the sharp objects away from your body. 
• Always hold the handles of sharp objects. 
• Sharp pointed tools should be stored in a tool box. 
• Make sure that a hoe or axe is never leaning against an open door or on uneven floor. They could fall over, or someone could trip on them.