# Physics 13 Using Rollers

Remember a simple machine doesn’t change the amount of work you do. You will still move an object the same distance. What a simple machine does is make that work take less effort. Are rollers a simple machine? What are rollers anyway?

These are not the kind girls use to curl their hair.

Question: How do rollers work?

Materials:

Book

String (scissors to cut it)

Rubber band

Six or seven round pencils

Procedure:

Wrap the string one and a half times around the book

I used a smaller book. The book could be twice as thick and this project will still work.

Cut off the piece of string

Tie a loop in one end of the string

The loop can be an inch or a little more long. If it is less than half an inch, it will be harder to attach it to the rubber band.

Put the other end of the string through the rubber band and the loop

The end of the string goes through the rubber band first and then the string loop.

Pull the string tight

The string loop must be pulled tightly to the rubber band so it will not slip pulling the book later.

Tie the string around the book

The string should be tied around the middle of the book so it will pull evenly across the table.

Use the rubber band to pull the book across the table

Set the book back at the beginning

The pencils should be fairly evenly placed so the book can move from one to the next without falling off.

Space out the pencils so three will be under the book and the others in front of it

Set the book on the last three pencils

Use the rubber band to pull the book across the pencils

Observations:

Describe how the rubber band behaves as you pull the book on the table

Pulling the book across the table creates friction for the entire surface. Friction makes the book harder to pull.

Describe how it feels pulling the book on the table

Describe how the rubber band behaves as you pull the book across the pencils

Describe how it feels pulling the book across the pencils

Conclusions:

Assuming you pulled the book the same distance both times, did you do the same amount of work? Why do you think so?

Was it easier to pull the book on the table or on the pencils?

The pencils roll as the book is pulled over them making the name rollers apt.

What did the pencils do under the book as it went over the top of them?

Why would the pencils be called rollers?

Can you think of another name for a roller? What is it?

What I Found Out:

My book had a slick book cover on it so it pulled across the table easily. The rubber band stretches out at first then sprang back once the book started moving. The book dragged a little on the table.

The rubber band barely stretched before the book started pulling over the pencils. It moved very fast over the pencils. The book didn’t drag at all.

The pencils do roll but some roll better than others. They are not attached to the book so they bunch up losing their spacing.

Since work is the distance times the mass, I did the same amount of work. The mass of the book and the distance did not change with and without the pencils.

What did change is how easy it was to pull the book over the pencils. The pencils turned and rolled under the book.

The pencils could be called rollers because that is what they did: rolled. Something else that rolls is a wheel.

# Physics 12 Double Levers

Scissors are so useful. They are one of several common double levers.

Take a look at a pair of scissors. Each blade moves like a lever: one end goes down pushing the other end up.

Where is the fulcrum on a pair of scissors? Remember the lever turns on the fulcrum which remains in place. On double levers the fulcrum is where the two levers cross each other and are fastened together.

I forgot to take a picture of my scissors. You know what they look like, don’t you? These are double levers. Do you see where the fulcrum is?

Get a piece of cardboard and a pair of scissors. Where should you put the cardboard to cut it the easiest? Close to the fulcrum or far away?

Let’s review how a fulcrum increases force. Get a 200 page book and 2 pencils. Prop the book on the end of one pencil. Put the second pencil crosswise under the first pencil to act as a fulcrum. Try lifting the book with the second pencil away from the book and near the book. Which placement makes lifting the book the easiest?

Should the cardboard be near the fulcrum of the scissors or farther away? Double check by trying to snip the cardboard from both positions.

Pliers are a useful tool around the house. They can be used for gripping things or turning tight small lids. Do you see the two levers?

Another of the common double levers is a pair of pliers. Perhaps you have one to look at. Where is the fulcrum? Why are the handles for your hand to grip longer than the gripping ends of the levers?

Tin snips are used to cut sheet metal, flat plates of metal. The length of the handles can vary. As the handles get longer, will the snips part get more powerful?

On the farm I have another of the double levers. It’s called tin snips. These are used to cut sheets of metal such as metal roofing. If you don’t know anyone with a pair of these, you can look at the picture. Find the fulcrum. Like the pliers, one end of the levers is longer than the other.

Perhaps you can find some other double levers around your house. How do you recognize them?

What I Found Out:

The book lifted the easiest when the fulcrum pencil was close to the book. In the same way, putting the cardboard close to the fulcrum made cutting it much easier.

On both the pliers and the tin snips like with the scissors the fulcrum is where the two levers cross and has the bolt connecting the two.

Double levers are easy to recognize because they have two long pieces crossing each other and joined where they cross. That join is the fulcrum. Others I found included pruners for trimming plants, loppers for cutting brush and bolt cutters for cutting thick wires up to 1/2 inch thick.

# Physics 11 Mass a Coin With Levers

Last Project we found out we could balance a heavy object with a light one by moving a lever over the fulcrum. Can we do this to mass a coin?

Question: Can a lever be used to mass a coin?

Materials:

Piece of thin cardboard 3 cm x 28 cm

Dime

Balance

Metric ruler

Table

Procedure:

Mark a line 2 cm from one edge of the cardboard piece

Label the line R

The real purpose of the R line is to mark one end of the lever to tell the ends apart. It marks a good place to set the coin.

Place the cardboard piece on the edge of the table

Slide the piece over the edge of the table until it balances on the edge

As the cardboard lever moves out over the edge of the table, the end begins to rise. Take care it does not rise too far or the lever will slip to the floor.

Mark this point and draw a line across it

Label the line E

Measure the distance from line R to line E to the nearest mm

Mass the cardboard piece

Remember that a lever balances when the mass is equal on each side of the fulcrum.

Set the cardboard piece on the edge of the table

Set the dime centered on the line labeled R

Slide the cardboard piece over the edge until it balances on the edge

Mark this point and draw a line across it

Label this line 1

Measure the distance from the R side of the cardboard to line 1 in to the nearest mm

Mass the dime

Observations:

Mass of:

Cardboard:

Dime:

Distance:

R to E line:

Line 1:

Analysis:

Divide the line R distance by the line 1 distance for a mechanical advantage for the dime

Line 1 is where the lever balances with a dime on the R line. Go a millimeter too far and the dime slides down flipping the lever onto the floor.

Multiply this mechanical advantage by the mass of the cardboard to get a mass for the dime

Conclusions:

How important is balancing the cardboard to mass a coin?

How important is it to measure accurately?

Where is the fulcrum for your lever in this Project?

A lever has two arms. What were the two arms for the lever in this Project?

Do you think a lever is a good way to mass a coin? why do you think this?

What I Found Out:

Balancing a piece of cardboard on the edge of a table is harder than it sounds. I slid the cardboard piece out until it seemed balanced. When I moved toward my camera, it slid onto the floor. I started over again.

Since the distances are being measured to the millimeter and one of these is small, It’s important to get as close to the final balancing point as possible. Any breeze makes this impossible.

I used a regular ruler with centimeters and millimeters on one side and inches on the other. It helps that the 0 line for the centimeters is not on the edge of the ruler. This makes it easier to get an accurate starting place. If the 0 line was the edge of the ruler, I would have started on the 1 cm line and deducted the 1 from the reading. one reading did come out between two millimeter lines. I used the closest line for the distance.

It takes care to keep the lever perpendicular to the table edge. You have to tap it lightly in the center, not on a corner to move it slightly until it balances.

I again had the lever slide to the floor with the dime on it. When I balanced the lever, the line R distance was 9.5 cm and the line 1 distance was 18.5 cm. The mechanical advantage was 0.51. Multiplying this by 3.5 g gave a coin mass of 1.9 g for the dime. My dime had a mass of 2.3 g on the scale. The two masses were close.

The edge of the table was the fulcrum. The R line marked one arm of the lever. The E line marked the other arm of the lever.

I don’t think this is a very good way to mass a coin. Finding the true balancing point is difficult. A regular ruler is not very accurate for measuring. There are too many places where errors can creep in.

# Physics 10 Exploring Levers

The Greek Archimedes once said that given a fulcrum and a lever, he could move the world. Levers are another simple machine. What is it and how does it work?

Question: How do levers work?

Materials:

Wood slat 40 cm long by 5 cm wide

Triangular or 1” wood block [I found the 1” block works best.]

Several weights, 2 the same, 1 heavier, 1 lighter

Scale

Ruler

Pencil

Procedure:

Place the block on a table

The slat is not exactly level. This shows as my measurement of each end gave two slightly different values.

Place the wood slat on the block moving it back and forth until it balances

Note: The slat is your lever

Mark the balancing point

Measure from the end of the slat to the line from both ends

Mass your weights unless they are from a weight set so you know the masses

Keeping the balancing point over the fulcrum, place a mass at one end of the slat

Placing a mass on one end causes that end to drop to the table while the other end rises.

Observe what the lever does

Place the identical weights, one at each end

Adjust the slat until it is again in balance

Take one weight off

Place the light weight on the other end of the slat

A teeter totter on a playground behaves this way when a heavier person sits down on one end. How can this person make it balance so both people have fun?

Move the slat back and forth until it balances

Measure the distance from the balance point over the fulcrum to each weight

Remove the weights

Return the slat to the original balancing line

Place the heaviest weight on one end of the slat and a lighter weight on the other end

Predict how you will need to move the slat to balance the two masses

Move the slat until the two are in balance

Observations:

Mass of weights

Distances:

From ends to balancing line

From masses to balancing line

Same mass weights

Mass and light mass

Mass and heavy mass

Describe what happens:

When you balance the slat

When one mass is put on one end of the slat

When the two identical weights are on the slat

When the light weight is put on one end

When the light weight is balanced

When the heavy weight is put on the slat

Prediction of where the slat will balance

When the heavy weight is balanced

Analysis:

Multiply the mass times the distance for the two identical masses

Multiply the mass and distance for the mass and the light mass

If you consider the formula of Fd = Fd it explains why a heavy mass is at a short distance to balance with a light mass.

Multiply the mass and distance for the mass and the heavy mass

Conclusions:

Compare the lengths when the salt is balanced.

If you could mass each end of the slat, how do you think these would compare?

Draw the lever, fulcrum and one mass

Put arrows to show where the forces are acting on the lever system

The mass exerts mass downward on one end of the lever. That puts an equal upward force under the other end. The force vectors are equal and opposite so the center, on the fulcrum, has no net force acting on it.

Why does the slat balance at the same place when two equal masses are balanced?

How does the mass x distance results compare for the two identical masses?

How do these results compare for the light weight and the heavy weight?

A rule for levers is that the force times the distance for one arm or side equals the force times the distance for the other arm or side. Do you think this is correct? Why do you think this?

How can this be used to move a heavy object?

What I Found Out:

I tried using a triangular fulcrum. The slat would balance on the edge but it was very difficult to do this. It worked much better to use the 1” board piece as a fulcrum. I did have to watch that the slat was level as it would balance a little before it was really level.

I was in a hurry. I hope you take your time. My lever is not quite balanced between the 20 g and 50 g masses. You can tell because the slat is not level.

When I balanced the slat on its own, the ends measured 37.0 cm and 38.7 cm. This was nearly equal. The two ends would have the same mass as the slat would be divided in half.

The mass pushes down on the lever so it sinks to the table top. That means a force is pushing up the other end.

When I put masses of equal mass on the ends of the slat, the force pushing on each end was the same, the total mass of each end remained the same so it would balance at the same place as it did without the masses.

The balancing point puts equal mass on each side of the fulcrum. since the masses are equal, the rest of the set up is equal.

My two equal masses gave 740 g-cm and 772 g-cm. When I looked at the pictures of this, the slat wasn’t completely level so the two were probably even closer in size.

When I balanced the lighter mass, the slat moved the heavier mass closer to the fulcrum. The distances were 30.0 cm for the 50 g mass and 43.0 cm for the lighter20 g one. This gave the Fd values as 150 g-cm and 91.2 g-cm. The distances for the 500 g mass was 13.0 cm and 62.6 cm for the 50 g mass. The Fd values were 6500 g-cm and 3030 g-cm.

The Fd values for my experiment weren’t very close. This is the rule a lever normally follows so I need to look over my Procedure and Observations more closely.

The idea of a simple machine is to do the same amount of work using less effort. A lever would do this if the distance to the heavy object was short and the distance to where the force is applied is long. A long distance times a small effort will equal and larger effort over a short distance.

# Physics 9 Simple Machine Called Wedge

Perhaps you have learned to sew on a button. Take a close look at the sewing needle. One end is a point. The needle gets thicker the farther up the needle you go. This is one kind of wedge.

A yarn needle for sewing with yarn is large so it’s easy to see the pointed end and how the needle thickens going away from that end.

Find a door stop, one of the brown rubber kind that is pushed under a door to keep it open. Look at it from the side. It has a point and gets thicker farther from the point. this is another kind of wedge.

Maybe you know someone who carves wood. Ask to see a flat chisel. Look at it closely top and from the side. It starts at a broad point and gets thicker as you go away from the point. A chisel is a wedge.

Look at a wood chisel. Is it a wedge?

Question: How does a wedge work?

Materials:

Sewing needle

Piece of cloth

Procedure:

Look at the piece of cloth observing the thread pattern

Hold the piece of cloth

Push the needle through the cloth

Observe what the cloth does

Observations:

Describe and draw part of the piece of cloth

Describe how the cloth threads change as you push the needle through

From the side it’s easy to see a wood chisel has a point at the end the slopes up from there.

Special Section on Wedges:

Look at the pictures of a splitting maul. Does it look like the other wedges? Why do you think so?

A splitting maul has a typical wedge shape. The end comes to a broad point. The maul gets thicker going away from the point. Unlike the chisel this wedge goes out in two directions. The needle goes out evenly all around. All have a point.

Splitting mauls are used to split firewood. Usually the maul is swung down so the head hits the piece of wood. This is repeated as the crack in the wood widens until the piece splits into two pieces.

For this I used the maul as though it did not have a handle to show how the maul splits the wood. First I tapped the maul until it stood up in a piece of wood.

Even tapping the splitting maul enough so it will stand up creates a crack in the piece of wood.

Then I hit the top of the maul with a sledge hammer. This applies force to the top of the maul. Where does this force go?

The maul goes down into the piece of wood so some of the force pushes the maul downward.

The crack in the wood gets wider. Does some of the force go sideways? Why do you think so?

As the splitting maul goes further into the wood, the split gets wider. This crack follows the grain in the wood going to the center of the piece then splitting into two paths.

Conclusions:

When you push on a needle, you are applying force. Where does that force go?

How is a wedge like an inclined plane?

How is a wedge different from an inclined plane?

What I Found Out:

My piece of cloth had threads running up and down and other threads going across. The threads went over and under each other. They were tight so the threads did not shift.

When I pushed the needle through the cloth, the point went through between the threads and pushed them apart. After the needle went through the cloth, the threads tried to go back into place but left a small hole where the needle had been.

The splitting maul has a broad point and gets thicker going away from the point. It is a wedge.

The force goes into the maul. Part of the force goes down and pushes the maul further into the wood.

Part of the force pushes the wood apart. There must be force pushing the wood apart. The only place any force is being applied is on the top of the maul. Some of it pushed the wood apart.

An inclined plane has a broad point at one end and gets thicker going away from that point.

An inclined plane sits still. Objects are pushed or pulled up the ramp.

Force is applied to a wedge. That force pushed the wedge forward and pushes outwards to push things apart.

# Physics 8 Exploring How Screws work

What do a pencil sharpener, a screw, a scissor jack and an inclined plane have in common? Find yourself several different kinds of screws and take a look.

Common screws have one of two heads. The top one is a straight slot and takes a regular screwdriver. The bottom one has a cross slot and takes a Philips screwdriver.

Note: The raised metal going around a screw is called a thread. The top is called the head. Some screws have slots on their heads and take straight screwdrivers. Some have crossing slots and require a Philip’s screwdriver.

Question: How do screws work?

Material:

Several different screws, same diameter but different threads

Screwdrivers for the screws

Block of wood with drilled holes the size of the screws in it

Ruler

Procedure:

Examine one of the screws closely to see how the threads are arranged

Hold a screw between your finger and thumb turning it with the other hand

The screw turns into the wood a tiny bit then the head cuts into my fingers as I try to turn it a little more and can’t make it budge.

Put the end of the screw in a hole in the board and try to turn the screw several turns using your fingers then use a screwdriver.

Take that screw out of the hole

Find two screws with different threads, one with threads far apart and one with threads close together

Start these two screws in the board until they stand up by themselves

The head is shaped like a wood screw’s head so this screw is used for wood. Fine threads are often used for fine work such as furniture.

Measure the height of the two screws

Turn each screw two complete revolutions

This was the longest screw as well as the one with the finest threads. If you measure from one thread down two, this should be the same as the amount turning the screw twice will put it into the wood. For this screw that was 0.2 cm.

Measure the height of the two screws

Observations:

How are the threads arranged on the screw?

How does it feel to turn a screw with your fingers?

How does it feel to turn a screw into the wood?

How it feels to turn a screw with a screwdriver

This is a wood screw with definite threads not too far apart but not real close together either. The top will fit into the wood so it won’t catch on anything rubbed over the wood later.

Height of the screws:

beginning

ending

At first glance this screw went in the farthest but it was the shortest so it really only went in 0.4 cm in two full turns.

beginning

ending

Conclusions:

If you could unwrap the threads on a screw, what simple machine would they become? Why do you think so?

Why do we use a screwdriver to put in a screw?

Compare how fast a screw with wide threads goes in to one with narrow threads.

Looking at the three screws it is easy to see the right one has fine threads and the left on has coarse threads. The middle one is in between the other two.

What I Found Out

When I held a screw and turned it, it crawled up between my fingers. It felt like my fingers were sliding up the threads.

Of course I can’t really take the threads off. But if I could, the thread would become a slanted line and be like an inclined plane from the bottom to the top of the screw. I think that because the thread is a continuous line going up the shaft.

This is a deck screw. It has widely spaced threads to make it easy to put it into coarse wood. The top is angled to fit into the wood smoothly so the deck surface will be smooth.

Trying to put a screw into a hole in the wood using fingers does not work. The very tip will go in but then the fingers can’t turn it anymore. A screwdriver gives more power to my hand and makes the threads go into the wood.

After two full turns the coarsely threaded screw was only 1.5 cm high. It went in 0.6 cm.

My screw with fine threads started at 2.6 cm and ended at 2.3 cm so it went in .3 cm. The medium threads started at 1.7 cm and ended at 1.3 cm going in .4 cm. The coarse threads started at 2.1 cm and ended at 1.5 cm going in .6 cm.
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