IMPORTANT TERMS

Fluids                          Liquids and gases are together known as Fluids.

Net force                     Overall force acting on an object.

Atmosphere                 Covering of air around the earth

Manometer                  An instrument used for measuring the pressure of a fluid.

Barometer                   An instrument used to measure atmospheric pressure.

Newton (N)                   The SI unit of force.

Pascal (PA)                  The SI unit of pressure.

 

FORCE AND ITS EFFECTS

A push or pull acting on an object is known as Force.

Force can make a stationary object move or make a moving object move faster.

Force can change the direction of an object e.g. in a game of Tennis, the force applied by the player changes the direction of the ball.

Force can change the shape of an object e.g. force applied by a potter with his hands changes the shape of the clay and converts it into pots.

Forces applied on an object in same direction add to one another.

If two forces are applied over an object from opposite directions, the total effective force is the difference of the two forces.

The force on an object is zero, if the two forces acting on it in opposite directions are equal in magnitude.

Strength of a force is expressed by its magnitude and direction. If the direction or magnitude of the applied force changes, its effect also changes.

 

CONTACT FORCES

A contact force is a force between two objects that are in direct or indirect physical contact with each other.

 

MUSCULAR FORCE 

The force resulting due to the action of muscles is called Muscular force. This force can be applied only when it is in contact with an object. It is because of this force that human beings, as well as animals are able to perform various tasks. E.g. pushing an object, lifting a bucket of water.

FRICTION

Friction is the resistance to motion experienced when two surfaces in contact move with respect to each other. Friction is the force that stops the free movement of the objects by preventing its smooth glide on the ground.

NON-CONTACT FORCES 

Forces that do not need physical contact with the objects on which they are acting are called non-contact forces.

 

ELECTROSTATIC FORCE

Electrostatic is a type of force that is exerted by a charged body on another charged or uncharged body. It pulls lighter objects towards itself once it is charged. Electric air purifiers in factories use this concept to purify the air from its chimneys.

MAGNETIC FORCE

Magnetic force is a kind of force that magnets exhibit to pull or push other magnets and metal objects like iron and nickel. If the same pole of two magnets are placed near each other they will repel, while if unlike poles are placed near each other they attract each other.

GRAVITATIONAL FORCE

Gravitational force is a kind of force that pulls everything towards the centre of the Earth therefore, a ball thrown up comes down due to gravity. The force of gravity acts on all objects.

 

PRESSURE

Pressure is defined as the force per unit area.

Pressure is proportional to the surface area in contact.

Increasing the area over which a particular force acts thereby decreases the pressure produced.

Decreasing the area over which a particular force acts thereby increases the pressure produced.

 

PRESSURE EXERTED BY LIQUID AND GASES

Both liquid and gases exert pressure in all directions (Downward, upward and sideways) on the walls of the containers that holds them. 

In liquids, pressure increases with depth. The pressure exerted by water, deep under the sea is much greater than that at the sea level. The sea-divers wear specially designed suits to protect themselves from this pressure.

 

ATMOSPHERIC PRESSURE

The pressure exerted by the air around us is known as Atmospheric pressure. Atmospheric pressure decreases as the altitude increases.

Astronauts wear specially designed suits while going into space because there is no air pressure in space. Spacesuits provide them oxygen to breathe while they are working in space.

 

INTERESTING FACTS

• Pascal was named after French physicist and mathematician Blaise Pascal.
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• Sir Isaac Newton was one of the first scientists to study gravity and force.
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• Gravity keeps Earth and the other planets in our solar system in orbit around the Sun. It also keeps the Moon in orbit around Earth.
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• A compass has a tiny magnet in it. The arrow always points to the North Pole.
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• The Earth would be as lifeless as the Moon without the atmosphere.
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• Torricelli discovered air pressure in the 1640s. He made the first barometer by turning upside down, a glass tube filled with mercury (a heavy liquid metal) in a bowl.
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• At very high altitudes, atmospheric pressure and available oxygen get so low that people can become sick and even die.
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• In a barometer, a column of mercury in a glass tube rises or falls as the weight of the atmosphere changes. Meteorologists describe the atmospheric pressure by how high the mercury rises.
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• Our lungs can rip away from the rib cage at deep depths.
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• Many sea-animals have no trouble at all with high pressure. Whales can withstand pressure changes because their bodies are more flexible.