Worksheet
23
Simple Machines
force
Simple machines are tools that make our work easier by applying force
Fill in the blanks using words from the box
easy,
pulley. Inclined,
planes are also called ramos.
A simple machine makes our work
3. The
that we apply on the lever is called effort
becomes a machine when it is combined with an axle
Answers
Answer:
Throughout history, humans have developed several devices to make work easier. The most notable of these are known as the "six simple machines": the wheel and axle, the lever, the inclined plane, the pulley, the screw, and the wedge, although the latter three are actually just extensions or combinations of the first three.
Because work is defined as force acting on an object in the direction of motion, a machine makes work easier to perform by accomplishing one or more of the following functions, according to Jefferson Lab:
transferring a force from one place to another,
changing the direction of a force,
increasing the magnitude of a force, or
increasing the distance or speed of a force.
Simple machines are devices with no, or very few, moving parts that make work easier. Many of today's complex tools are just combinations or more complicated forms of the six simple machines, according to the University of Colorado at Boulder. For instance, we might attach a long handle to a shaft to make a windlass, or use a block and tackle to pull a load up a ramp. While these machines may seem simple, they continue to provide us with the means to do many things that we could never do without them.
Wheel and axle
The wheel is considered to be one of the most significant inventions in the history of the world. "Before the invention of the wheel in 3500 B.C., humans were severely limited in how much stuff we could transport over land, and how far," wrote Natalie Wolchover in the Live Science article "Top 10 Inventions that Changed the World." "Wheeled carts facilitated agriculture and commerce by enabling the transportation of goods to and from markets, as well as easing the burdens of people traveling great distances."
The wheel greatly reduces the friction encountered when an object is moved over a surface. "If you put your file cabinet on a small cart with wheels, you can greatly reduce the force you need to apply to move the cabinet with constant speed," according to the University of Tennessee.
In his book "Ancient Science: Prehistory-A.D. 500" (Gareth Stevens, 2010), Charlie Samuels writes, "In parts of the world, heavy objects such as rocks and boats were moved using log rollers. As the object moved forward, rollers were taken from behind and replaced in front." This was the first step in the development of the wheel.
The great innovation, though, was in mounting a wheel on an axle. The wheel could be attached to an axle that was supported by a bearing, or it could be made to turn freely about the axle. This led to the development of carts, wagons and chariots. According to Samuels, archaeologists use the development of a wheel that rotates on an axle as an indicator of a relatively advanced civilization. The earliest evidence of wheels on axles is from about 3200 B.C. by the Sumerians. The Chinese independently invented the wheel in 2800 B.C. [Related: Why It Took So Long to Invent the Wheel]
Force multipliers
In addition to reducing friction, a wheel and axle can also serve as a force multiplier, according to Science Quest from Wiley. If a wheel is attached to an axle, and a force is used to turn the wheel, the rotational force, or torque, on the axle is much greater than the force applied to the rim of the wheel. Alternatively, a long handle can be attached to the axle to achieve a similar effect.
The other five machines all help humans increase and/or redirect the force applied to an object. In their book "Moving Big Things" (It's about time, 2009), Janet L. Kolodner and her co-authors write, "Machines provide mechanical advantage to assist in moving objects. Mechanical advantage is the trade-off between force and distance." In the following discussion of the simple machines that increase the force applied to their input, we will neglect the force of friction, because in most of these cases, the frictional force is very small compared to the input and output forces involved.
When a force is applied over a distance, it produces work. Mathematically, this is expressed as W = F × D. For example, to lift an object, we must do work to overcome the force due to gravity and move the object upward. To lift an object that is twice as heavy, it takes twice as much work to lift it the same distance. It also takes twice as much work to lift the same object twice as far. As indicated by the math, the main benefit of machines is that they allow us to do the same amount of work by applying a smaller amount of force over a greater distance.