5th class secine effect of forces on motion of an object | inertia | lever and its kinds | simple machines

 6.8 Effect of Forces on Motion of an Object

Two equal but opposite forces are acting on a moving object like vehicles. One bigger force produced by engine pushes car in forward direction. The other smaller force produced by air resistance pushes car in backward direction.

What do you conclude?

6.9 Inertia

If something is at rest, it is at rest.If an objects is moving, it will continue its motion unless some external forces change its state. For example, a book lying on a table will remain there unless someone picks it up by applying force on it. Similarly, a ball thrown on the ground will remain in motion unless some external force like air friction does not act upon it.

The tendency to resist a change in the state of motion or rest of an object is called inertia. Inertia depends on mass of an object. Light accessories are more twins than lightweight items.For example, it is difficult to push a bus than a bicycle because bus has more inertia than bicycle. More people can push a bus while a single man can push a bicycle easily.

6.10 Wedge

A wedge is also a simple machine. It is a piece of wood or metal that is thick at one end and sloping to a thin edge at the other. A wedge is made when two inclined planes join together. These joint inclined planes form a triangular shape having a short edge. A wedge is used to separate a body into parts or cut an object into two pieces. The example of wedges are axe, knife, and knitting needles, etc.

Inclined Plane

Perhaps you noticed an inclined plane when oil drums are loaded on a truck. The loaded drum is rolled over the inclined plane to the truck. Why is it done like this? This is because it is easier to roll over on inclined plane than to raise things vertically. So an inclined plane makes the job easier.

 So, to roll a body over inclined plane, the distance to be covered is greater but the force to be applied is small.

6.11 Lever and its kinds

Simple machines like knife, scissors, crowbar, wrench, broom etc., are called levers. Even likes our legs, hand and fingers.By them we can move, shift or raise things and can apply force in many different ways. When a crowbar is used to raise a heavy box, it acts as a lever. Here the crowbar is supported by a stone or brick or something hard. You apply small force on one end and get the force multiplied on the other end.Lever makes work easy to do and also increases the force. So, a work that normally requires a great force, can be done easily with the help of a lever by applying a small force.

Parts of Lever

A lever consists of three parts.

1.  Effort

2. Fulcrum

3. Load

The lever is supported on a dot or line of a hard object. The lever moves or rotates centering this dot or line. This point or line is called the fulcrum of the lever. The heavy object which is to be raised by a lever is called load and is kept at one end of the lever. On the other end of the lever, force is applied The distance between fulcrum and load is called Load arm and the distance between fulcrum and the place where force is applied is called force arm.

Kinds of levers

The fulcrum of the lever will not always be between load and force. It may be at one end too. Depending on the position of fulcrum, load and force lever is classified in three categories.

First Kind of Lever: 

When fulcrum is in between the load and force, the lever is called first kind of lever. For example, Scissors, balance etc.

Second Kind of Lever:

 In this kind of lever, fulcrum and force are at the two ends and the load remains at the middle. Nutcracker is an example of this type of lever. Two parts of cracker are joined at a point, this point is the fulcrum. Force is applied by hand at the other end point and load is exerted on the nut at the middle.

Third Kind of Lever:

 In this class of lever, force is applied to the middle in between load and fulcrum Example of such levers are tong or forceps.

6.12 Simple Machines

We know that force is required to do work. However, there are some techniques of applying forces so that work becomes easier to perform. 

Some work that requires enough force can be done with minimum force if the proper technique is followed. The technical devices that we use to do work easily with minimum force are called simple machines.

 The common examples of simple machines are lever, pulley, wheel and axle, inclined plane, and wedge, etc.

How simple machines work?

How you can lift a heavy box from ground? You take help of some people who together hold the box and raise it. Definitely, the later method is easier. In this case, the work is done by applying less force. 

Only you have applied a trick by using a simple machine i.e.. rod. This simple machine has made the work done easy with minimum effort.

We use many simple machines in our daily life, such as knife, scissor, pliers, crowbar, and lever etc.