# 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.

# Physics 6 Meet the Inclined Plane

You are going to visit a friend and run up to the porch. How are you going to get onto the porch? You can jump up or you can walk up the steps.

Jumping up may be more fun. Walking up takes less effort. Those stairs are one kind of inclined plane.

Hailyann Workman’s help was greatly appreciated on this project. She seemed to think this was fun to do.

Question: How does an inclined plane work?

Materials:

3 Boards or pieces of stiff cardboard 10 cm wide and 0.5 m, 1 m and 1.5 m long

3 Bricks or 3 books about 5 cm thick

Spring scales

Meter stick

Block with loop

Procedure:

Set up the pile of books

Measure the height of the pile of books

Stand the block next to the pile of books

Use a spring scale to lift the block onto the books recording the force in grams

Remove the block

Measure the length of the boards

A short ramp is steep. Since work is force times distance, the longer distance makes the amount of work much higher.

Lean the short board on the pile of books to form an inclined plane or ramp

Set the block just on the edge of the board

Use the spring scale to pull the block up onto the books recording the force needed

Repeat this for each of the other boards

Observations:

Height of book pile:

Length of short board:

Length of medium board:

Length of long board:

Force needed:

To lift the block

Short board

Medium board

Long board

Analysis:

Calculate the work needed to get the blocks onto the books by multiplying the force on the scale times the height of the books. This is W = Fd or Work = Force times distance.

Using a simple machine is supposed to reduce the force needed to get the same amount of work done. Now that we know how much total work is needed, we can calculate the force needed for each of the inclined planes by rearranging the formula so W/d = F or work divided by distance equals force.

Calculate the force needed for each inclined plane.

Go back to the Procedure to complete the Project

Conclusions:

Compare the force you measured for each inclined plane with the force you calculated.

Compare the force needed for each ramp with the force needed for the others and to the force needed to lift the blocks.

A longer ramp has less of a slope making it easier to pull the blocks up.

What happens to the distance you must pull the block to use less force?

Would it be better to lift or use a ramp for a lightweight object? Why do you think so?

Would it be better to lift or use a ramp for a heavyweight object? Why do you think so?

What is the advantage of using a ramp?

What I Found Out:

This week I found Hailyann Workman to help me do this project. She is five and in kindergarten. She thought pulling the blocks up a ramp fun to do.

My stack of books was 15 cm tall. The scale registered 200 g lifting the blocks up. The work done was 3000 g-cm.

The short ramp was 44.5 cm long. The scale showed 150 g needed to pull the blocks up the ramp. I calculated 67.4 g-cm.

Next the blocks went up a 74 cm ramp using 100 g of force. I calculated needing 40.5 g-cm.

Remember finding out about friction last week? My long ramp was rough making lots of friction. Covering the ramp with paper made it smooth.

The long ramp was 109 cm and rough. It was hard to pull the blocks up so I taped paper onto the ramp to make it smooth. The blocks pulled up easily with 70 g of force needed. My calculated amount was 27.5 g-cm.

My measured forces were much higher than my calculated forces. Perhaps I misread the scale. My block was smooth but not slick. My ramps were not slick so there was friction.

The needed force did decrease as the ramp got longer. The medium ramp took half the force of lifting the blocks.

The distance increases as the force needed decreases.

A lightweight object can be lifted up to move it the shortest distance. A heavyweight object should be moved up a ramp. This takes more distance but requires less force and is easier on you than lifting something heavy.

A ramp is a way to decrease the force needed to move an object even though it increases the distance needed to move it.