FORCES
A force pushes or pulls. It squashes or stretches. It presses on an object or any other form of matter. It may make the object move in a certain way (motion) or change its shape (deform). One of the main forces that acts throughout the Universe is the gravitational force. Another is the electromagnetic force. These two forces can act at a distance. That is, they do not have to be in contact with an object or touching it.
Physical forces act when two objects are in contact. Hammer a nail into wood, and the force of the hammer hitting the nail makes it push down into the wood’s fibres. This is a force causing motion. The wood pushes back with its own resisting force. As the nail goes deeper the resisting force of the wood increases. It may eventually become equal to the force of the hammer hitting the nail. At this stage the nail stops moving. The next blow may bend the nail. This is a force causing deformation.
A plane flies due to a balance of forces. The Earth’s gravity pulls it down, but it is balanced by the upward force of lift produced as the specially shaped wings pass through the air.
A flying plane is slowed down by air resistance as it pushes aside molecules of air. This backwards force, drag, is balanced by the forwards force of thrust from the engines.
PRESSURE
The force of a hammer blow pushing a nail into wood acts over a tiny area – the nail’s point. The same hammer blow might not make a blunt nail enter the wood because the force is spread out over a larger area. The amount of force for a certain area is called pressure. A sharp knife cuts because the force moving the blade is concentrated into the tiny area of the blade’s edge, giving very high pressure. Force is measured in units called newtons after scientist Isaac Newton. Pressure is measured in newtons per square metre.
Picture Credit : Google
