Tag Archives: needle

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.

needle is 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.

wood chisel

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

wood chisel shows wedge characteristics

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?

maul has wedge characteristics

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.

wedge point focuses force from the wedge

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?

wedge puts force down and out

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.