Lifting machines can be divided into two groups: complex and simple. The complex ones were born later and are so called because they can be broken down into more basic machines, while the second ones cannot be broken down. Furthermore, simple machines are machines that were already present in ancient times and are based on muscle strength. Any device that offers resistance with only the muscular force called motor is a simple machine. Some examples of simple machines used for the construction of the walls are: lever, pulley, winch, winch, wheel, inclined plane, hoist, screw.
The gain of car
In simple machines, there is the driving force Fm which represents the force applied by the user and the resisting force Fr which is the force to be overcome or balanced. G gain of a machine is defined as the ratio between the resisting force and the driving force: G = Fr / Fm if the driving force is less than the resisting force G> 1 and the machine is said to be advantageous. If the driving force is greater than the resisting force G <1 and the machine is said to be disadvantageous. If the driving force is equal to the resisting force G = 1 and the machine is said to be indifferent.
The winch is a simple machine that consists of a cylinder and a wheel fixed to each other and rotating around a common axis. Two forces act on it, motive force and resisting force acting by means of ropes. The equilibrium condition is obtained when the moment of the forces for the length of the respective arm and the radius of the base of the cylinder are equal and opposite. The winch is therefore a third kind of lever, because the driving force is applied between the resisting force, the rope, and the driving force, the crank, and is always disadvantageous. Nonetheless, it can be used to drag or lift heavy weights using a driving force that is little less than the resisting force.
The inclined plane is a machine that allows the lifting of bodies consisting of an inclined surface that connects the plane on which the body to be lifted is placed with that in which the same body must be moved. The lifting of bodies occurs by making them slide on the plane applying a smaller driving force. On the inclined plane, the resistance is split in two and so the power must only counteract the resistance Fpx parallel to the inclined plane. As a result of the decomposition of forces, the force necessary to move a body on an inclined plane is always less than that which would be needed to lift it. Consequently, the lower the angle of inclination of the plane and the lower the power to be applied.
The winch is an advantageous first kind of lever, it is a machine that is used to move weights through the use of a rope or chain and it is a horizontal cylinder which, made to rotate, wraps the rope on which the resistance is applied. The power has a much greater arm than that of resistance the longer the crank. The power is applied to the crank attached to the drum which rotates thanks to a gear that multiplies the input force. The winch is widely used for lifting bodies and for tensioning ropes.
Its main use is the lifting of loads. We can find both fixed and mobile pulley. The fixed pulley can be considered a lever as it remains fixed in its ‘o’ center, and the pulling force and a load in which the two arms are equal are applied to it. A rope runs on it at the ends of which the resisting force Fr and the driving force Fm act. Therefore, in a fixed pulley, a driving force of the same intensity must be applied to balance the resisting force. The gain G = Fr / Fm is equal to 1 and therefore this machine is indifferent in relation to the mechanical advantage. The mobile pulley, on the other hand, is considered a second kind lever to which a force is applied with an arm of the driving force double that of the resisting force.
The hoist or compound pulley is made up of a system of pulleys connected by ropes and chains by which the force required to lift the weight is reduced; the effort reduction factor depends on the number of pulleys used. It was used to lift very heavy objects such as stones, columns or architectural elements in general, in fact it has the function of amplifying human strength.