Simple Machines – Inclined Plane, Wedge and Screw
• Look at the objects shown on these pages. Which of them would you call machines?
• Would it surprise you to find out that each is ____________________________________
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• As you learned in the last section, a machine helps you do work by ________________
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· There are six basic kinds of simple machines: ____________________________________
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• In this section, you will learn how the different types of simple machines help you do work.
Inclined Plane
Have you ever had to lift something from a lower level to a higher level?
• The job is much easier if you have a ___________________________________.
• For example, a ramp makes it much easier to push a _____________________________
_____________________________________________________________________________.
• A ramp is an example of a simple machine called ________________________________.
• An inclined plane is _________________________________________________________.
How It Works
• An inclined plane allows you to exert your ____________________________________
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• As a result, the input force needed is ___________________________________________.
• The _________________force that you use on an inclined plane is the force with which _____________________________________________________________________________.
• The _________________ force is the force that you would need to ___________________
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• Recall that this force is equal to ________________________________________________.
Mechanical Advantage
You can determine the ideal mechanical advantage of an inclined plane by dividing the _____________________________________________________________________________.
• Ideal Mechanical Advantage =
· For example, if you are loading a truck that is ______ meter high using a ramp that is_____ meters long, the ideal mechanical advantage of the ramp is ______ meters ÷______ meter, or __________.
• The inclined plane increases the force you exerted _______________________ times.
• If the height of the incline does not change, ______________________________________ of the incline will _____________________________________________________________.
• The _____________________ the incline, the _______________________ you need to push or pull an object.
• Although the amount of work is the same whether you lift the boxes or push them up the ramp to the truck, you need ______________________ when you use an inclined plane.
• When you use a ramp, what happens to the distance over which you exert your force?
Wedge
• If you’ve ever sliced an apple with ______________________, pulled up _________________________ or seen someone chop wood with ______________, you are familiar with another simple machine known as _______________________________.
• A wedge is _________________________________________________________________
_____________________________________________________________________________.
• It might be helpful to think of a wedge, like the one shown below, as _____________________________________________ (or sometimes two inclined planes back to back) _____________________________________________________.
The Forces of a Wedge
• The __________________________________ exerted on a wedge results in _______________________________ that can split the log.
• You have probably never given much thought to the zippers
on your clothes.
• But zippers use _________________________________________________
_________________________________________________________________.
How It Works
• When you use a wedge, instead of moving an object along the inclined plane, you ___________________________________________________________________________.
• For example, when an axe is used to split wood, the axe _________________________
__________________________ on the blade of the axe, which is ______________________.
• That force pushes ____________________________________________________________.
• The wedge in turn exerts _________________________________ at a 90° angle to its slope, splitting the wood in two.
• Wedges are a part of your everyday life. For example, ___________________________
_______________________________.
· A __________________________________________________________________________ all make use of wedges.
Mechanical Advantage
• The mechanical advantage of the wedge and ___________________________________ are similar.
• The ideal mechanical advantage of a wedge is determined by ______________________
______________________________________________________________________________
• The ____________________________ and __________________________ a wedge is, the _____________________________ its mechanical advantage.
• For example, the cutting edge of a ______________________________________________ is a wedge.
• When you sharpen a knife, you make the wedge ______________________________ and ______________________________ its mechanical advantage.
• That is why __________________________________________________ than dull knives.
Screws
• Like a wedge, a screw is a simple machine that is related __________________________
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• A screw can be thought of as _________________________________________________
__________________________________________________________.
• This spiral inclined plane forms the ____________________________________________.
How It Works
• When you twist a screw into a piece of wood, you exert ___________________________ on the screw.
• The threads of a screw act like __________________________________________ to _____________________________________________________ over which you exert the input force.
• As the threads of the screw turn, they __________________________________________, pulling the screw into the wood.
• ________________________ between the screw and the wood holds the screw in place.
• Many devices act like screws. Examples include _________________________________
_________________________________________________.
• Look at the jar lid in Figure 15.
• When you turn the lid, your ____________________________ is greatly _________________________________because of the _______________________________
____________________________________________.
• The threads on the lid are pulled against the matching threads on the jar with a strong enough force to ______________________________________________________.
Mechanical Advantage
• The _______________________________________________________ of a screw are, the ____________________________________________________________________.
• This is because the closer the threads are, the __________________________________
________________________to fasten it into a piece of wood.
• Your input force is applied over ___________________________________________.
• The longer input distance results in an _________________________________________.
• Think of the length around the threads as the length of the inclined plane, and the length of the screw as the height of the inclined plane.
• The ideal mechanical advantage of a screw is ____________________________________
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A Paper Screw
• To make a paper model of a screw, cut out a triangle from a piece of paper.
• Tape the wide end of the triangle to a pencil. Then wind the paper around the pencil.
Making Models How does this model represent a real screw? ______________________
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Can you think of a way to calculate the ideal mechanical advantage of your model screw?
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What is the mechanical advantage of your model screw? ___________________________
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• The length around the threads of a screw is the same as the
– height of an incline plane.
– width of an incline plane.
– length of an incline plane.
– output distance of an incline plane