Forces Harry Finch 10SS2 Harry Finch
Types • There lots of different types of forces. • Static • Dynamic • Internal Resistance • Tension • Compression • Torsion • Shear force • Friction • Air resistance • Spring • Gravitational • Electrical • Magnetic
Group 1 – Contact Forces • Friction - is the force between two surfaces rubbing together. When two smooth surfaces rub together there is very little friction. When two rough surfaces rub together there is more friction. There is less friction when there is a liquid (e.g. oil) between the two surfaces. There is more friction if the two surfaces are forced against each other. It can be good and bad. • Tension - is the force which is transmitted through a string, rope, cable or wire when it is pulled tight by forces acting from opposite ends. The tension force is directed along the length of the wire and pulls equally on the objects on the opposite ends of the wire. • Air Resistance - is a force which act in the opposite direction that you are travelling (except in space, where there isn't any). It is caused by molecules of air colliding with an object, causing it to slow down and eventually stop. Air Resistance can also be known as drag. • Spring - A spring is an object that upon use of a force in a given direction compresses and then, after removal of the force, decompresses or springs back to its original dimension. Spring force is the description of the force that causes the spring to rebound.
Group 2 – Action at a distance • Gravitational – is an attractive force between matter. Gravity is one of the four fundamental forces of nature (the others are the electromagnetic, nuclear, and weak forces). For instance, gravity holds the planets together, keeps us on the surface of the Earth, and keeps the planets in orbit around the Sun. It was dicoverd by Isaac Newton. • Electrical - The force resulting from the difference between existing charges. Coulomb's law''' is a law of physics describing the electrostatic interaction between electrically charged particles. • Magnetic - Every magnet has a north and south pole, just like the earth. Opposite poles attract - so the north pole attracts the south pole and the south pole attracts the north pole. Like poles will repel each other - so if you place two north poles together or two south poles together they will push each other away. A magnet's strength is strongest at the poles and weakest in the middle. The space around a magnet is called a magnetic field. It is this invisible area where the force of a magnet can be felt. For example, the closer you bring a paper clip to a magnet, the more you will feel the pull of the magnetic field.
Others • Static - An example of this is a person holding a stack of books on his back but he is not moving. The force downwards is STATIC. • Dynamic - An example of a dynamic load is a person carrying a weight of books but walking. The force is moving or DYNAMIC. • Internal Resistance - A person is sat on a Unicycle and the air filled tyre is under great pressure. The air pressure inside it pushes back against his weight. • Compression - A weight lifter finds that his body is compressed by the weights he is holding above his head, Because the weight is pushing down on him. • Shear force - An example of shear force is with scissors. The two handles put force in different directions on the pin that holds the two parts together. The force applied to the pin is called shear force.