Introduction: (Initial Observation)
All machines make the work easier. Without using machines many tasks are virtually impossible. Although simple machines are used as useful tools, most machines are a combination of two or more simple machines. Such machines are called compound machines.
Compound machines help us to cut and form material, lift heavy objects, transport heavy objects or more complex tasks such as packaging, sewing, mixing and many more.
The main challenge in design and construction of any compound machine is to decide how the pieces must be connected to each other.
In this project you will construct a compound machine that is comprised (made of) at least two different simple machines.
In this project guide I will provide you with some sample designs for compound machines that you may make at home. You may modify the designs or just use those as ideas to come up with your own designs.
Adult supervision, assistance and support is required for this project. This is a multi-level project; do not attempt on experiments that well exceed your abilities.
Find out about simple machines and compound machines. Read books, magazines or ask professionals who might know about compound machines that can be made at home using paper, cardboard, plastic, wood and metals. Find out how different simple machines may be connected to each other as parts of a compound machine. Keep track of where you got your information from.
Following are samples of information that you may find:
Simple machines are types of devices that do work with one movement. These devices were all in common use for centuries before Leonardo’s time. Each one makes work easier to do by providing some trade-off between the force applied and the distance over which the force is applied.
There are 6 simple machines; the inclined plane, the wedge, the screw, the lever, the pulley, and the wheel and axle.
A single pulley simply reverses the direction of a force. When two or more pulleys are connected together, they permit a heavy load to be lifted with less force. The trade-off is that the end of the rope must move a greater distance than the load.
A wedge converts motion in one direction into a splitting motion that acts at right angles to the blade. Nearly all cutting machines use the wedge. A lifting machine may use a wedge to get under a load.
A screw is a central core with a thread or groove wrapped around it to form a helix. While turning, a screw converts a rotary motion into a forward or backward motion.
A lever is a stiff rod that rotates around a pivot point. Downward motion at one end results in upward motion at the other end. Depending on where the pivot point is located, a lever can multiply either the force applied or the distance over which the force is applied.
Gears are toothed or pegged wheels meshed together to transmit motion and force. In any pair of gears the larger one will rotate more slowly than the smaller one, but will rotate with greater force. Each gear in a series reverses the direction of rotation of the previous gear.
Compound machines are two or more simple machines working together. A wheelbarrow is an example of a complex machine that uses a lever and a wheel and axle. Machines of all types make work easier by changing the size or direction of an applied force. The amount of effort saved when using simple or complex machines is called mechanical advantage or MA.
Additional information about simple machines:
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
The purpose of this project is to construct a model of a compound machine. A compound machine is made of 2 or more simple machines.
Another example of question/ purpose:
The purpose of this project is to construct a model of a compound machine used to lift a heavy object and measuring the mechanical advantage of the machine and see how does the machine reduce the amount of force required to do the work for different loads (or different values of resistance force).
(required for experimental projects)
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
Constructing a compound machine is an engineering project, thus it does not require defining variables. If you are required to define variables, then you may use the following sample.
The independent variable (also known as manipulated variable) is the Resistance Force. In elevators, cranes and other devices used to lift heavy objects, the resistance force is the weight of the object that you are trying to lift.
The dependent variable (also known as responding variable) is the is the effort force. Effort force is the actual force that you use in order to lift an object using an elevator, crane or lever.
(required for experimental projects)
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.
Constructing a compound machine is an engineering project, thus it does not require a hypothesis. If you are required to suggest a hypothesis, then you may use the following samples:
- In the elevator that I am planning to make, the effort force is always less than the resistance force. I expect the effort force be 1/10th of the resistance force.
- In a pulley set that I am planning to make, the effort force is not always less than resistance force. For small resistance forces, the effort force may be much higher due to the friction between pulley parts.
Note that you just need to have one hypothesis of one project.
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
Select one of the following designs to construct a model of a compound machine.
Compound machine 1: Winch
Introduction: Winch is a compound machine used for hoisting or hauling. Winch has a drum or spool around which is turned a rope. The other end of the rope is attached to the load being moved. As the spool turns, it winds and pulls the rope and the load.
Winches are used to pull boats out of the water. They are also used to pull trucks or other heavy weights up a steep hill. Winch is a compound machine using wheel and axle as well as lever simple machines.
You will need the following pieces to construct your winch:
- Wooden base – 5″ x 7″
- 2, flat wooden posts – 7 1/2″ x 1 1/4″ (l x w)
- 1, flat wooden piece – 2″ x 1 1/4″ (l x w)
- 1, longer wood dowel – 6″ x 3/8″ (l x d)
- 1, shorter wood dowel – 2″ x 3/8″ (l x d)
- 1 wood spool – 3/4″
- 4 nails – #18 x 3/4″ wire nails
- Nylon string, twisted mason line – 2 feet
1. Make a mark in the middle of one of the posts 1/2″ from the edge.
2. Put the post with the mark on top of the other post and hold them tightly.
3. Using a 1/4″ drill bit, drill a hole through both posts.
4. Attach the two flat wooden posts in the middle of the longer sides of the base using two nails on each post.
5. Insert the longer wood dowel through the wood spool.
6. In the small flat wooden piece, make a mark for two holes in the middle, 1/2″ from each end. Make the holes using 3/8″ drill bit.
7. Insert the shorter wood dowel in one of the holes and apply some glue.
8. Insert the long wood dowel with the wood spool through the two holes in the posts and attach the handle on one end. Apply some glue to the handle only as the dowel will have to spin inside the posts.
9. Roll some string onto the spool and you are now ready to use your winch. As you turn the the handle, the string will wind or unwind and make it possible to lift or lower a weight. Such weight may be called a load or a resistance force.
Compound machine 2: Pulley system
Introduction: Pulley systems are used in cranes, lifts and elevators of different types. With a simple pair of quad pulleys you may increase the force by about 8 times. Pulley systems are also used in elevators. Usually elevator motors do not have enough force to lift the heavy structure of an empty elevator. These are pulleys that increase the force and make it possible for an elevator motor to lift the elevator with passengers. In this activity you will make 2 quad pulley sets and use them in a pulley system.
- 2 small hook screws
- One small eye screw
- 8 sheaves
- 2 nails (2.5″ long, 1/8″ diameter)
- 2 wood blocks 1.5″ x 1.5″ x 0.5″
- 4 wood blocks 1.5″ x 2.5″ x 0.5″
- Nylon string (Mason line)
- 4 small nails
- wood glue
Sheaves are available at MiniScience.com; all other parts are available at hardware stores, craft stores and home improvement stores.
Get 2 pieces of 1.5″ x 2.5″ x 0.5″ wood blocks for the sides of one pulley, mark the place where the long nail must enter as the shaft for 4 sheaves. Also mark the place where small nails will enter to connect the sides to the top piece.
Use a drill to make holes where the nails are going to enter.
Get a 1.5″ x 1.5″x 0.5″ block of wood as the top side of the pulley; make a hole on the center of that for hook screws, apply some glue on two opposite edges and connect the pulley sides as shown the above diagram. Apply 2 small nails to secure the sides while the glue dries.
Pass the big nail through one side of the pulley, 4 sheaves and the other side of the pulley.
Insert the hook screw in the top side of the pulley so it can be hanged. Your first quad pulley is ready now.
Use the same method to make a second quad pulley.
Insert a small eye screw in the lower side of one pulley and hang this pulley somewhere as your fixed pulley.
To string the pulleys tie one end of the string to the eye screw and then pass it through the sheaves of both pulleys as shown in the picture.
Hang a heavy object or a basket to the lower pulley (moving pulley) and pull the free end of the string to feel how much force do you need to lift the heavy object.
The mass of the object being lifted is the load or the resistance force.
The force that you apply to lift the object is the effort force.
Compound machine 3: Elevator
Introduction: In this experiment you will use the same plastic sheaves and a few pieces of wood to make a new pulley system and use it as an elevator.
The pieces you will need to construct your very own pulley elevator are the following:
- wooden base – 5″ x 7″
- 2, flat wooden pieces –
- 1, flat wooden piece –
- 1, flat wooden block – 4″ x 2 1/2″ x 1/4″
- Nylon twisted mason twine – 10 feet
- 5, plastic pulley sheaves
- 8 nails – #18 x 3/4″ wire nails
- 5 screws – #4 x 3/4″ sheet metal screws
- 1 screw hook – 7/8″ cup hook
- 1 weight (optional)
1. Mark out 1/4″ from both edges on the longer side of the base.
2. Using two nails, nail in one of the longer flat wooden pieces where you have made your mark. Do the same on the other side where you have the other mark.
3. Attach the cross bar (the shorter flat wooden piece) at the top of the two posts you had attached.
4. On the cross bar, mark three spots for the centers of the sheaves. The first sheave should be centered 35mm from the edge. The next sheave should be centered 95mm from the edge. The last sheave should be centered 155mm from the edge.
5. Screw three sheaves into the holes you have made using three screws. Test to make sure that the sheaves can easily turn.
6. In the wooden block, make marks for the two sheaves. The holes should be 1″ from the top of the block and 3/4″ from the side of the bock.
7. Screw in the two sheaves along with the cup hook similar to the picture.
8. Attach one end of the nylon twine to the block and run the other end up to the first sheave, then down the the first sheave on the block, then up to the second sheave on the crossbar, then down to the second sheave on the block and up to the last sheave on the crossbar. The end will be used to elevate and lower the weight attached to the hook.
9. Pictures below show two different ways that this pulley system elevator may be constructed.
10. Hang a heavy object or a basket to the lower pulley (moving pulley) and pull the free end of the string to feel how much force do you need to lift the heavy object.
The mass of the object being lifted is the load or the resistance force.
The force that you apply to lift the object is the effort force.
Compound machine 4: Power Lift
Introduction: A compound machine can have any combination of 2 or more simple machines. In the power lift machine suggested in this experiment, you will use a wheel and axle with a combination of pulleys in a wooden structure.
- 2, flat wooden piece 3″ x 12″ x 1/2″ (upper and lower sides of the frame marked as A and B)
- 2, flat wooden piece 3″ x 14″ x 1/2″ (left and right sides of the frame marked as C and D)
- 2, flat wooden piece 3″ x 4″ x 1/2″ (left and back support for the wheel and axle marked as E and F)
- 5″ long 3/8″ wood dowel (wheel and axle)
- 2″ long 3/8″ wood dowel (crank handle)
- 1 piece of 3″ x 1″ x 1/2″ (crank)
- 3 single pulleys
- Cotton or nylon string (Mason line)
- Nail, hammer, wood glue, drill
In the molding wood section of a home improvement store you may purchase a 6 feet strip of 3″ x 1/2″ molding and then cut the lengths that you need.
Label the pieces from A to F as shown.
Place E over D, align their bottom edges and make a hole 3″ away from the bottom edges. This hole must be slightly larger than the wood dowels that you are using, so the wood dowel can spin freely. These holes are the supports for the wheel and axle.
Wheel an axle is made of the small 3″ x 1″ x 1/2″ and two pieces of wood dowels. First mark the location of the holes exactly 1/2″ from each end of the crank piece. Then make the holes exactly the same as the diameter of wood dowels; and finally apply some wood glue to one end of each wood dowel and insert them in the holes. Your wheel and axle crank is ready now.
Construct the frame by connecting the pieces A, B, C, D, E and F. In each connection apply some wood glue to the contact surface and then apply some small nails to hold them in place.
Insert wheel and axle in the holes in D and E.
Insert 3 hook screws in E and hang the fixed pulleys.
Tie one end of the string to the first hook, pass it through the movable pulley, pass it through the two fixed pulleys and wrap it around the wheel (wood dowel).
With the help of a hole, a nail or some adhesive tape secure the end of wire on the wheel.
Hang a basket or a platform to the movable pulley. Turn the crank to pull up the moving pulley and the basket.
Add some heavy objects to the basket and test to feel how much force do you need to lift it by turning the crank.
The exact amount of effort force can be measured by using a 100-gram spring scale to turn the crank.
To calculate the mechanical advantage of your machine for different amounts of resistance force, you must measure the effort force for different loads.
Following is a sample results table:
|Load/ Resistance force/
Mass being lifted
|Effort force/ force used to turn the crank||Mechanical advantage = R / E|
Such results table can also be used to draw a graph.
Materials and Equipment:
Following is a suggested list of material for experiment number 1.
- Large 6-volt battery known as lantern battery
- 2 identical glass thermometers
- Very thin wire
- Wooden board
- plastic rod or tube (such as a pen) or wood dowel
- Test tube
- Spring Scales 100-gram and 250-gram.
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
No calculation is required for this project.
Summary of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Your conclusion may be answers to the following questions:
Did the compound machines you made ease the work of lifting an object?
Explain how did the machines ease the work.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.