Chapter:-Force and pressure

Force

A push or pull is called force, a body at rest starts moving only when a force is applied 

  

Effects of force

Force can changes 

1) Speed 

2) Direction of an Object

4) Shape 

5) Size .

 

Types of forces 

1) Muscular Force 

2) Contact Force 

3) Non-Contact Force

4) Frictional Force.

 

1)     Muscular Force :- The force applied by the execution of our own muscles. Loosely speaking,we can call this muscular force .

 

2) Contact Force:- The type of force can act only when it is in contact with a body. You cannot push a table along the floor unless your hands are in contact with it called contact force..

 

3) Non Contact Force:- There are some forces which can act on a body from a distance .such forces are called Non Contact Force.

 

4) Frictional Force:-Frictional Force acts in a direction opposite to that of the motion, contact force is called frictional force, the smoother the surface , the lesser is the frictional force..

 

Static friction and kinetic friction 

*static friction, when acts when a body is stationary,is greater than kinetic friction,which acts when a body is moving .

 

When friction is helpful-

Life will be quite difficult without friction.we can't walk .similarly , without friction between the tyres and the road , vehicles would skid , brakes of vehicles will also not work , we cannot write without friction, we require friction to light a matchstick.

 

When friction causes problems 

Friction makes surface wear down . The soles of shoes get worn out ,many parts of machines rub against each other , the sandpaper will wear down the eraser much faster because vit is rougher, friction wastes too much energy .

 

How  can to Reduce the Force of Friction ?

Reducing friction

As we know friction wastes energy , way to reduce friction is to make the surface in contact smooth by polishing, another way is oiling ,is to use ball bearing or roller bearings .

 

Streamlined bodies

A streamlined body has smooth outlines .when such a body moves through water or air , it disturb natural flow . This reduce  the resistance offerd by air or water to its movement ..

 

How can to Increase the Force of Friction?

Increasing friction

Some time it is advantage to increase friction, the tyres of our vehicles have grooves to increase friction , if they were smooth there would be risk of slipping , it is to improve grip .

 

Magnetic force

The force with which a magnet attracts such things is called magnatic force , magnatic force, muscular force, frictional force can act from a distance .

 

Electrostatic force

The force which acts on the pieces of paper is called electrostatic force .

 

Gravitational force

Any two bodies in this universe attract each other by a force called gravitational force, this is known as Newton’s Law Of Gravitational.

 

Weight

A spring balance is used to measure weight of a body. Weight depends on mass of a body, You can use a beam balance to measure weight of a body.

 

Unit of force 

Si unit of force is Newton, the weight of a 100g mass or the force of gravity acting on it is 0.98N . Therefore, the weight of a 1kg mass -9.8 N .

 

Pressure

The force per unit area,is called pressure.

Pressure- Force  /  Area 

The SI unit of pressure is newton's per square meter

The less the surface area and there will be more pressure.

 

Pressure exerted by liquids

A liquid too have mass and it is attracted by the force of gravity,this acts downwards on the base of the container.

The pressure exerted on the base of the container is the weight of the liquid divided by the area of the base. .

 

Measuring liquid pressure

A manometer is an instrument used to measure pressure differences.you can make a simple manometer and use it to see how the pressure of a liquid changes with deapth .

 

Atmospheric pressure

U know that we are surrounded by a blanket of air . This air has mass and it is attracted by force of gravity ..

 

*Why a can or bottle get crushed?

Because first,the steam from to the boiling water drives the air out of it . Then, when u close the lid and cool the can or bottle ,the steam condenses, leaving empty space . Air pressure , which u normally do not feel,acts on all sides of the can and makes it cave in  .

 

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 Written By - Amiteshwar Singh