The elements in a lever are:

● Load “L”: is the force we have to lift or

overcome.

● Effort “E”: is the force exerted by the

user.

● Load arm “La”: distance between the

load application point and the fulcrum.

● Effort arm “Ea”: distance between the

effort application point and the fulcrum.

claws, pliers, etc.

opener, the nutcracker, etc.

With these levers we always get mechanical advantage as the effort arm is always longer than the load arm.

stapler, the hockey bat, a fishing rod, a broom, the tweezers, the ice holder, etc.

With this kind of lever no mechanical advantage is obtained as the effort arm is always shorter than the load arm.

Instead, we gain in speed of the load or movement of it.

The elements in a lever are:

● Load “L” (carga o resistencia): is the force we have to lift or

overcome.

● Effort “E” (esfuerzo o potencia): is the force exerted by the

user.

● Load arm “La” (brazo de resistencia): distance between the

load application point and the fulcrum.

● Effort arm “Ea” (brazo de potencia): distance between the

effort application point and the fulcrum.

The drive element of a pulley mechanism is usually a rope, cable, belt or chain that runs over the pulley inside the

groove.

A simple pulley (also called fixed pulley) doesn’t increase the speed of the rope nor

reduce the effort needed to move a load.

E = L

The only advantage is to reduce friction and to change the direction of the rope to

help us with our own weight.

With this mechanism we get mechanical advantage of 2 because the load is hanging

from two parts of rope and we just pull on one of them, the other one is tied to a

fixed point. In exchange, we’ll have to pull the rope two metres if we want to lift

the load 1 meter.

Usually, the moving pulley is used in combination with another

fixed to get the advantages of both of them. This mechanism

is called block and tackle (polipasto o aparejo)

belt moves the driven pulley. Both pulleys rotate in the same direction. This mechanism is reversible, which

means that we can use both wheels as driven or as driving wheels.

The transmission speed ratio is the same as in the friction wheels.

axles. The gears rotate in opposite direction. The speed of the driven gear depends on the number of teeth of both

gears.

pairs to transmit rotary motion where the bevel gear shafts are at right angles

(90 degrees) to each other.

For the speed transmission we use the same equation we know from spur gears.

Bevel gears are reversible as well.

wheel meshes with the chain and pulls it as it rotates. As the chain moves, the driven wheel turns.

Bicycles and motorbikes use sprockets and chains

because of their greater strength and the fact that

they do not slip.

The speed ratio is the same as with the spur gears.

As well as the spur gears it is a reversible mechanism.

When the pinion (circular gear) turns, it meshes with the teeth of a linear “gear” bar, so it moves linearly.

This mechanism is reversible, which means that the rack can also make the pinion turn.

of it. And if we turn the nut while locking the screw, then the nut will move back or forth depending on the turning

direction of it.

unroll depending on the turning direction to the crank. This way, the load attached to the rope will move up or down.

It is the system used to lift buckets in water wells or in fishing rods. We can use the lever’s law in a whinch, considering the

length of the crank as the Effort arm and the radium of

the spool as the Load arm.

movement in the rod (biela). It is a reversible mechanism, so if we make the rod move back and forth, we will get a

rotary motion in the crank or the eccentric.

designed to move up and down as it follows the edge of the cam. The same function of the cam can do it an

eccentrics (excéntrica)