# C ONTENTS What is force? How to measure force? Types of forces Impact force Strain force Magnetic force Electrostatic force Gravitational force.

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C ONTENTS What is force? How to measure force? Types of forces Impact force Strain force Magnetic force Electrostatic force Gravitational force

W HAT IS FORCE ? A force is defined as either a push or a pull. It has 5 effects- 1) a force can make an object move. E.g. if you throw a basketball your muscles exert a pushing force on the ball. a force can make an object stop. E.g. a goalkeeper moves into the path of a moving ball to exert a pushing force on it and stop the ball. a force can change the speed of a moving object. E.g. a hockey player uses his stick to hit a slow moving ball and send it past the goalkeeper. a force can change the direction of a moving object. E.g. a batsman can change the direction of a ball by deflecting it so that it moves away from the wicket and races away to the boundary. a force can change the shape of an object. E.g. when we press a sponge we apply a force which changes its shape and the moment we release the force, the sponge returns to its original shape.

H OW TO MEASURE FORCE ? Force is measured with a Newton spring balance. The S.I. unit for measuring force is called Newton. This force is small and is equivalent to the pulling force required to peel a banana. Newton spring balance.

T YPES OF FORCES There are 2types of forces : 1. Contact force and the other is 2. Non-contact force. Contact force occurs when the object exerts the force by touching the material. Non- contact force occurs when the object exerts the force without touching the object. These forces are further divided into other forces.

I MPACT FORCE It is a type of contact force where a moving object collides with a stationary object. This force can be large as when a tsunami wave collides with building or very tiny as when a moving gas molecule strikes the skin. impact force

S TRAIN FORCE When some materials are bent, squashed, twisted or stretched they exert a force which acts in the opposite direction to the force acting on them. This force is called strain force and is a contact force. This force exerted by a deformed material brings the material back to its original shape. These materials are also called elastic materials. strain force

M AGNETIC FORCE It is non- contact force which acts when 2 magnets are bought closer to each other. As you know that opposite poles of a magnet when bought closer to each other attract and similar poles of a magnet repel, you will feel a force pushing your hands apart or a force pulling your hands together even though the magnets are not touching each other. The pushing force or the pulling force increases as the magnets are bought closer. This force is also applicable if a magnet exerts a pulling force on metals.

E LECTROSTATIC FORCE If electrical insulators are rubbed on oily materials a electrostatic charge develops in them. There are 2 types of charges – a positive charge or a negative charge. If this charged material is bought near an object it will attract or repel the object depending on the charges of both the material and the object. Similar charges repel and opposite charges attract. electrostatic force

G RAVITATIONAL FORCE In the universe, the force that exists between any 2 point masses is termed as gravitational force. The gravitational force between the earth and the moon keeps moon in its orbit and the gravitational force between the sun and all planets keeps the planets in their orbits. gravitational force

A PPLICATION OF FORCES 1. Different types of forces can be used in different ways. E.g.1) The concept of impact force can be used in shaping things. 2. In motor cars and jet planes, the burning of fuel produces enormous energy which results in force which is translated into motion. 3. The strain force concept is used for elastic materials as well as for making tall buildings and bridges. 4. The force between different electrons in an atom and between electrons and protons is used to make atom bombs and atomic reactors to produce electricity. Since electricity is nothing but electrons in motion.

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