Wedges & Screws: Definition & Examples

Instructor: Thomas Higginbotham

Tom has taught math / science at secondary & post-secondary, and a K-12 school administrator. He has a B.S. in Biology and a PhD in Curriculum & Instruction.

Wedges and screws are two of the six types of simple machines, and they are used in many different areas of our lives. In this lesson, learn about the similarities and differences between wedges and screws, and some examples of them that are commonly encountered.

Simple Machines

What do a potato peeler, a jack for a car, and a door stop all have in common? They're all variations of the inclined plane, one of the six simple machines. Now, when we say simple machine, we're not talking about a blender, or a lawnmower (though each of these complex machines depends on simple machines). We're talking about physics' simple machines that get work done in the world. In this lesson, we'll focus on wedges and screws, but first, a brief bit of information about simple machines.

So, what is a simple machine? Simple (sorry about that). It is a tool that changes either the direction or magnitude (increases or decreases) of a force. This idea is called mechanical advantage. Scientists back in the day (the Renaissance day, to be exact) commonly described six different types of simple machines, a classification scheme that is still used today. These six machine groups are levers, pulleys, wheel and axles, inclined planes, wedges, and screws. We'll get into the last three of these in a minute.

But first, to illustrate what 'changing the direction or magnitude of a force' means, lets think about a simple lever. There's no way a 50-pound child could lift their 200-pound dad, right? Wrong. They could use a lever, like a see saw. This particular lever can take the force of a child's weight, and increase its magnitude enough to lift the force of a much heavier object. It also changes the direction of the child's force, from down to up.

See Saw Lever

The thing to remember is that machines help us be more efficient with the energy we put towards a task.

The Inclined Plane

You've got to get a 200-kg block of ice up to a 4-foot ledge. Would it be easier to lift it straight up to the ledge from the ground, or use a ramp? Most of the sane among us would use a ramp. Physics-wise, how does the ramp help? There is a certain amount of work (force applied over a distance) that needs to be done to get that big block of ice up to the ledge. The ramp is an example of an inclined plane, a plane (i.e., straight edge) at an angle less than 90-degrees, which decreases the amount of force necessary to move the block of ice up to a certain place by spreading the required force out over the length of the ramp. The longer the ramp, the less the force required (think about a short, 45-degree ramp vs. a long, 10-degree ramp). Inclined planes generally don't move when providing their mechanical advantage. When an inclined plane is in motion, they are usually either wedges or screws.

The Wedge

What's a wedge? Well, let's think about the following. Would you rather use a butter knife or a precision-crafted ultra-sharp knife to cut through a piece of tough steak? Most of us would prefer the sharp knife. With a sharp knife, you provide (mostly) downward force to the knife in an attempt to cut through the meat. If you use the same force with each of the two knives, the force will be distributed over a larger area with the butter knife compared to the sharp knife, which focuses your force on one area of the meat, causing it to slice through more easily with the more focused force created by the knife.

Knife Blades

Another example of a wedge is a hypodermic needle. The sharper that wedge is, the more easily a medical professional can get it through to your veins.

A wedge is simply an inclined plane that moves to do its work. Examples include knives and anything with a blade (e.g., scissors, saws), axes, nails, and even teeth. Think about it - wouldn't you rather use your sharper front teeth to cut through an apple than your less sharp back teeth? Though most wedges are all about breaking things apart (knives, axes), some can hold things together, like a thumb tack (the wedge part of the thumb tack is the tip of the thumb tack).

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