TYPES OF FORCES
• Forces are acting everywhere in the universe at all times.
• There are different types of forces.
Gravitational force (Gravity):
• Gravity or gravitational force is the force that attracts objects to the centre of the Earth.
• Gravity is a key force in the universe, and it is the force which brought our planet into existence.
• Gravity is one of the simplest forces, and it can be illustrated through the classic story of Sir Isaac Newton and his apple.
• The story goes like that: Newton was pondering one day under an apple tree, when one fell down and struck him on his head.
• This set him thinking about the fact that there is some force acting on objects to pull them downwards.
• Gravity is a key force in the universe, and it is that force which brought our planet into existence.
• Everything in the universe has a gravitational pull, which drags other objects towards its centre.
• Gravitational force depends upon the mass of objects, but it can be observed in case of earth because it is huge. The moon is also subject to the earth's gravitational pull, and the earth is held in orbit by the sun's gravitational pull.
Figure 17: All these pictures depict that the ball comes/goes down due to gravity
• A book resting on a table has the force of gravity pulling it towards the Earth.
• But the book is not moving, so there must be opposing forces acting on the book.
• This force is caused by the table and is known as the normal force.
Figure 18: Normal force acting by an object
• If we place a thin piece of wood or plastic so that it is supported by both ends and place a small heavy object in the centre, the piece of wood will bend.
• Of course, it tends to straighten out so it exerts an upward force on the object. This upward force is the normal force.
• We can feel the force ourselves if we push down in the centre of the piece of wood.
• The harder we push, the more the wood bends and the harder it pushes back.
Magnetic force (Magnetism):
• Magnetic force is the push or pull applied by a magnet on metals and on other magnets.
• It is the force that attracts or drams in an object.
• Magnets have "north" and "south" ends, and the magnetic energy flows from the north to the South Pole.
Figure 19: Magnetic fields are not fully understood, but the basic principle is that opposite poles attract, and like poles repel. It can be demonstrated by using the magnets
• The earth also has a magnetic field, and that is why we can use compasses.
• Electrostatic force is the force of attraction between the charged objects.
Figure 20: A woman is running a comb through her dry hair, and the comb becomes charged and is able to attract tiny bits of paper. This attraction is due to electrostatic force
• When we rub a pen or a ruler against our woollen clothes, the pen or ruler will get charged.
Figure 21: A boy rubbing pen on his woollen clothes
• When we rub balloon against our hair, we can feel that our hair rises slowly as we lift the balloon.
Figure 22: A girl rubbing balloon against her hair
Situations Where the Effects of Electrostatic Charges can be Observed:
• When we get a plastic packet, the plastic sticks to our clothes.
• This happens because the packet rubs against lots of things which give it an electrostatic charge.
• When you rub your feet on the carpet and then touch a metal door handle you may get a small shock. This is due to the transfer of charge.