Simple Machines

Today we are going to talk about machines, specifically simple machines. Who knows what a machine is? Does it make things easier or harder? A machine is a device that makes work seem easier. It helps you put less effort in, but you will have to move it further. Who can give me examples of machines in this room? (they may give examples of compound machines…explain the difference after they’ve give examples. As you discuss the simple machines you want to draw them on the board.) Machines called simple machines are made of one or no moving parts. There are only six different simple machines – they are: the inclined plane, wedge, screw, lever, wheel and axle, and pulley. Six isn’t that many – that’s not that hard to remember, right? WELL, we can make it even easier. Sometimes it’s easier to remember things when we put them into groups; we can put them all into two different groups.

For instance, the inclined plane, wedge, and screw all have something in common. An inclined plane is just a sloping surface, such as a sliding board. Usually the inclined plane stays in one place and something moves up or down the slope. You slide down the sliding board. Just like all simple machines, an inclined plane makes work easier. A wheelchair ramp is another example. Some people find it easier to travel up the ramp than to take the stairs. Ramps also make it easier to load and unload a truck. A wedge looks like an inclined plane but differs in that you move a wedge (apply a force) to use it. An axe is an example of a wedge; how do you use an axe? You swing it. The screw is a little bit more confusing, but we’ll show you how it’s related in a little while.

Now what about the other three simple machines? How are they related? It’s easy to see how the wheel and axle and the pulley are related; a pulley looks a lot like a wheel and axle with a rope over it. But what about the lever? A lever doesn’t look much like a wheel and axle or a pulley. For starters, it isn’t even round! So you may be surprised to learn that the lever is the basic simple machine that the other two are based on. A lever is a bar with a balance point called the fulcrum. A garden shovel is an example. In a wheel and axle, the fulcrum is in the center. The outside rim of the wheel is like the handle of a lever; it just wraps all the way around. A pulley is just what it looks like, a wheel and axle with a groove to hold a rope around the outside edge.

Now that we’ve talked about these simple machines, who wants to do some experiments with them?

Optional Question to post to the class (now, or at the end of the lesson) and then go over answers in the final discussion. If you wanted to get to the top of a tall tower, what are some examples of simple machines you could use to get there? (Answer: A really, really long ramp (inclined plane); a spiral stair case (screw); an elevator (pulley). Other ideas for wedge, wheel and axle, and lever?)

After intro discussion, students should split up into 6 groups. These groups will move between the stations that have been set up. Some simple machines will take less time than others to demonstrate, but will have more experiments associated with them, so the time spent at each station should be about equal. It is easiest for each volunteer to do the same station repeatedly and just have the kids rotate.
Note: Volunteers should go over the worksheet together to confirm which diagram corresponds to each simple machine.

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Goggles are not necessary for any part of this lesson.

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Station 1 Supplies part 1:
Four planks of wood of varying lengths, with a screw in the top of each
Stack of textbooks or magazines
Bags of Barley (or other equally weighted bags)
Rubber Bands
Station 1 Supplies Part 2:
Several planks of wood
Stack of texbooks or magazines
Two or three pairs of barley bags, tied together with
String

Station 2 Supplies Part 1:
1 large, wide box
Uncooked Rice
Rectangular block of wood
Wedge shaped blocks of wood
Station 2 Supplies Part 2:
Stack of textbooks or magazines
Rectangular block of wood/small box
Wedge shaped blocks of wood with different angles Station 3 Part 1:
(These may be pre-cut. Check the supply box.)
Pencil
Paper
Colored felt tip marker
Station 3 Part 2:
Screws with various size threads
Block of wood
Screwdriver

Station 4 Supplies:
1 small block of wood for the fulcrum
1 large plank of wood for the leve Station 5 Part 1:
A long cylinder, like a broomstick
Station 5 Part 2:
Heavy book or board
wooden rods Station 6 Supplies:
Three pulleys (either real pulleys or hangers and thread spools)
Rope
Book (or weights)
Pole (to place across two chairs) Optional For Station 6:
Three students
Two broom handles
One ten foot long piece of rope

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Station 1:
Objectives: Students will learn that an inclined plane reduces the force necessary to bring an object from a lower elevation to a higher elevation by increasing the distance it must travel. Note: the amount the rubber band stretches is indicative of the force necessary to pull the object.
Procedure:
Set one of the planks of wood on a stack of textbooks or magazines so that it forms an inclined plane. Make sure the screw is at the top, and hang a bag of barley from the screw using a rubber band.
Does the rubber band stretch? What if I lift the top of the board higher (or add books?
Raise and lower the board to show how the length of the rubber band changes (it stretches more) when the incline is steeper. Then, set up the boards of different lengths (same book stack height).
What do you think will happen when we hang weights from these boards that are different lengths? Which one do you think will stretch the most? Why?
Test the hypotheses.
If you were going to use an inclined plan to get from someplace low to someplace high by walking up it like a ramp, which one would be easier to walk up? Which one would take longer? Set the plank of wood on a stack of textbooks or magazines so that it forms an inclined plane. Make sure there are extra books so that the height of the plane can be raised later. Tie the two bags of barley together with a length of string. First place one bag on the table with the other hanging over the edge (no inclined plane).
What do you think will happen when I let go? Will the bags move? Will the one hanging over the table fall?
Let go and let the bags slide off the table. Next, place one of the bags on the inclined plane with the other hanging over the edge. What happens to the bags now? Vary the height of the inclined plane (or set up several at once) and have the students compare what happens depending on the varying inclines. Encourage them to make predictions before each test.

Station 2:
Objective: Students will learn that it is easier to displace rice (or books) with a wedge rather than a block.
Explain to the students that the wedge is just like an inclined plane, but turned on its side. Ask them if they think it makes work easier when it is narrower or thicker (narrower – that’s why it is harder to move the box through the rice and use it to push the books apart).
Procedure: Fill the box halfway or so with rice and place both pieces of wood at one end of the box. Make sure they are halfway submerged into the rice. First ask them which they think will be easier to push across, and have them explain. Have students take turns pushing the blocks of wood across the box . They should pay attention to which takes more effort, as well as what is happening to the rice as they try to push it. The students can also compare pushing the wedge through the rice in the “right way” versus in the wrong way. The volunteer should push down on the stack of magazines/books while the students take turns trying to lift the stack with the wedges and the rectangular block. Have them note which is easiest. Which takes longer to lift the books one inch up?

Station 3:
Objective: Students will learn, in part 1, that a screw is simply an inclined plane that is wrapped around a pole. In part 2, students will learn that it takes longer to screw in a screw with finer threads.
Procedure: Have students work in pairs and make a diagonal line on a square paper. Darken the line with crayon or marker on both sides of the original pencil line. Cut along the pencil line to form two triangles Ask the students if they notice if the triangle looks like a simple machine they’ve seen (inclined plane). Each partner may now use one of the triangles to roll around a pencil, starting at one of the sides (not the diagonal) and rolling to the point. What have you made? (screw) Count the number of coils around your vertical axis (straw or pencil). Is the pitch of the screw steep? Repeat using a rectangular paper. How does the number of coils and the pitch vary depending on whether you rolled from the long or short side? How does it compare to the first screw created?

Remind them that after this activity, it should be pretty easy to see how a screw is related to an incline plane.

Have the students try to screw the various screws into the piece of wood. Note the relationship between number of threads/distance between the threads and effort it takes to put the screw into the board. They should find that the screws with close together threads should be easier to screw in. You can also try having them turn two different types of screws the same number of times and seeing which one goes in farther. Was the screw that went in farther easier or harder to turn? Ask them what the tradeoff is for a simple machine making work easier? (it takes longer to do the work). You can show how more threads per distance means you have to rotate the screw more to go a linear distance into the wood. But more screws mean that each rotation digs less, meaning it is less work.

Station 4:
Objective: Students will learn that a lever requires a fulcrum and that to balance equal weights the objects must be equidistant from the fulcrum.
Procedure: Use the small block as a fulcrum and place the large plank over it to build a see-saw like structure. Have a volunteer stand on one end of it, and have the students try to lift the volunteer by standing on the other end. Change the position of the fulcrum and have the students note whether it becomes easier or harder. The volunteer can also move on the board.

Briefly explain that a lever is a stick that is free to pivot (move back and forth at a certain point). That point where the stick pivots is called a fulcrum. Where you place the fulcrum changes the effort you have to put into moving the thing on the other end.

Ask if they can give other examples of levers (see-saw, broom…)

Station 5:
Objective: Students will learn that wheels convert rotational force (torque) into a linear force or vice versa. Friction also plays an important role in the use of wheels. Students will learn that wheels tend to reduce the friction required to move an object.
Procedure: One student holds a stick with one hand in the middle while a partner places her/his hands on either side of the person holding the stick. The partner tries to turn the stick “wheel” while the person holding the middle tries to keep the stick from turning. Next, the partner moves her/his hands farther apart and tries to turn the wheel. The partner continues to move the hands apart until the wheel turns easily. The person’s arm acts as the axle, and the pole is the wheel. You may want to be careful with this experiment, as kids can get too excited about competing for strength with a broomstick. One option is you could hold the stick in the middle, so it is just a kid competing against you, “the authority”.

Have the students try to push the book on the table (flat). Then try the same thing with the straws or rods underneath the book. When was it easier to push the book? With the “wheels” underneath. Why? The wheels reduce the surface area in contact with the table and thus make it easier to push by decreasing friction. The force you are applying to the book is converted into a rotational force (torque) in the round wood rods (wheels) which is then converted back into a linear force at the table. (If this last part seems too complicated, don’t worry! Explain as much as the students can understand.)

How does the wheel and axle make work easier? What if you wanted to slide down a hill; would it be easier to slide down by sitting there, or would it be easier to slide down sitting on a skateboard? What about if you wanted to transport 50 books from your class room to the school library. Would it be easier to make one trip per book, or all the books at once? What could you use to transport that many books at one time?

Station 6:
Objective: Students will learn that pulleys redirect forces. Pulleys can also be combined to reduce the force required to lift an object at the cost of having to lift twice the distance.
Procedure: Place the pole across the back of the chairs. Attach one pulley to the middle of the pole. Attach the other pulley to the book. Try pulling the book up when the rope goes through the pulley attached to the pole and is directly attached to the book. Now try looping the rope through the pulley on the book as diagramed below. Which setup is easier? The second setup should require half of the force but require you to pull twice the distance of the rope as compared to the first setup.

Setup 1 explanation: While the kids are pulling down (or horizontal) on the rope, the book is moving upwards. Ask the kids how else you might get the book to lift off of the floor (e.g. pull the rope without the pulley or simply lift the book). This concept is a bit difficult but try to explain to the kids that the pulley is redirecting the force: You are pulling downwards and the book is moving upwards.

Setup 2 explanation: This setup is a bit more complicated than setup 1. The idea here is that it is easier (requires less force) to pull the book up than it did in setup 1. You do, however, have to pull further. It is not necessary for the kids to understand the setup, but try to get them to notice that it is easier (feels lighter) to pull the book up. Also notice that you are still redirecting the force: you are pulling downwards and the book is moving upwards. Is there something you could do to this setup to have pull upwards and have the book move upwards?

Optional For Station 6 Procedure: Have one student tie the end of the twine onto one of the broom handles. Have two of the students stand about two and one half feet apart so that the broom handles are
held about two feet apart. Wrap the twine around the broom handles twice. Have the third student pull on the twine as the other two students try to hold the broom handles apart – tell students to keep the bars steady and avoid jerking motion. That way the force holding the brooms apart is more constant and the kids may be less wild. Now wrap the twine around the broom handles two more times and have the third student pull on the twine once more. Is it easier to move with more or less loops? Based on this result, do you think more or less pulleys would make a job easier? What is the tradeoff for using more pulleys? Do you see how we had to pull the rope farther?

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Important Concepts for the Day:
1. A machine is any device that makes work easier
2. A simple machine is made of one or no moving parts.
3. A simple machine can make a task easier, but you usually have to work longer to achieve the same goal.
4. There are six kinds of simple machines (the inclined plane, wedge, screw, lever, wheel and axle, and pulley), and you can group them into two categories (inclined plane and lever).
5. Within the two categories, the simple machines differ from one another in a number of ways including if they are stationary or used in motion and what direction the force in and force out are.
Note: We want to keep the explanation of these concepts as simple as possible for the students, focusing on Concepts 1-4.

To finish the day:

Now that we’re done with our experiments, let’s review what we went over. Who remembers how many simple machines there are? Let’s see if we can name them without looking at our worksheets! What is your favorite simple machine?
If there is time, you can also discuss examples of ways simple machines make work easier (transporting large loads, getting to the top of a tower, etc.)

Okay, so we’ve come to the end of our lesson. I want to ask you all a big favor. We’re going to do some of these experiment with the other classes in your grade soon, and it’s more fun for everyone if you don’t tell them any of the things we did today until they can do them on their own. So can you all please promise to try not to talk about these experiments with people who haven’t done them yet? Thanks! Look forward to seeing you again in a month for another lesson.

Thanks for learning about science with us!!

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Extra Information for the Volunteers (may be too complex for students): The six simple machines can be grouped into two categories: a lever and an inclined plane. The first three above (Inclined Plane, Wedge, and Screw) all fall under inclined plane, while the remaining (Lever, Wheel/Axle, and Pulley) all fall under lever. Within a category, the simple machines are differentiated based on whether there is an applied force and how the force is applied.
For example: an inclined plane is stationary flat surface that connects two different elevations. A wedge is simply an inclined plane with an applied linear force. A screw is an inclined plane which converts a rotational force (torque) into a linear force. The kids may find it hard to understand the difference between an inclined plane and a wedge so you should explain that the wedge is used in motion and the inclined plane is not. A good example to use for a wedge is an axe.
Be aware of time with this lesson. It’s very difficult to make it through all six simple machines in the allowed amount of time, and still do a wrap up discussion. A good idea is to plan a schedule of how long each group will spend at each station. Most of the stations should involve a quick setup (i.e. pouring rice into a box). For the screws and board experiment, it is best to pre-work the screws into the board to make it easier for the students. This will also prevent the students from trying to put a screw in a knot in the board. Since there are so many stations it might be best for each volunteer to take a station rather than a group of students for this lesson.

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No special clean up required.

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