Unit 2 Lesson 3 Machines
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Unit 2 Lesson 3 Machines
Work It Out
What do simple machines do?
• A machine is any device that helps people do
work by changing the way work is done.
• The machines that make up other machines are
called simple machines. The six types of simple
machines are levers, wheel and axles, pulleys,
inclined planes, wedges, and screws.
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Unit 2 Lesson 3 Machines
What do simple machines do?
• Work is done when a force is applied to an object
and makes it move.
• The work that you do on a machine is called work
input. The force you apply to a machine through a
distance is called the input force.
• The work done by the machine on an object is
called work output. The output force is the force a
machine exerts on an object.
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Unit 2 Lesson 3 Machines
What do simple machines do?
• Bottle openers and hammers are examples of
simple machines.
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Unit 2 Lesson 3 Machines
What do simple machines do?
• Work equals force times distance. If you apply
less force with a machine, you apply that force
through a longer distance. So the amount of work
done remains the same.
• Some machines decrease the magnitude, or size,
of the force needed to move an object. However,
you apply the force through a longer distance.
Other machines increase the amount of force
needed, but you apply the force over a shorter
distance.
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Unit 2 Lesson 3 Machines
What do simple machines do?
• Some machines change the way you do work by
changing the direction of a force.
• Some machines can change the direction of a
force, the magnitude of the force, and the
distance through which the force is applied.
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Unit 2 Lesson 3 Machines
In and Out
What is mechanical advantage?
• A machine’s mechanical advantage is the
number of times the machine multiplies the input
force. Mechanical advantage is a way of comparing
the input force with the output force.
• You can calculate the mechanical advantage (MA)
of any machine by dividing the output force by the
input force.
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Unit 2 Lesson 3 Machines
What is mechanical advantage?
• A machine that has a mechanical advantage
greater than one makes a task seem easier
because the output force is greater than the input
force.
• A machine that has a mechanical advantage equal
to one changes only the direction of the input
force.
• A machine that has a mechanical advantage less
than one allows you to apply a greater force over
a shorter distance.
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Unit 2 Lesson 3 Machines
What is mechanical efficiency?
• Mechanical efficiency is a comparison of a
machine’s work output with the work input.
• Mechanical efficiency (ME) equals the work output
divided by the work input, expressed as a
percentage.
• Ideally, the work a machine does on an object is
the same as the work that you put into it when
you apply a force. But in the real world, the work
input is greater than the work output because
some work is done to overcome friction.
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Unit 2 Lesson 3 Machines
Gaining Leverage
What are the classes of levers?
• A lever is a simple machine that has a bar that
pivots at a fixed point. This fixed point is called a
fulcrum.
• Levers are used to apply a force to move an object.
The force of the object is called the load.
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Unit 2 Lesson 3 Machines
What are the three classes of levers?
• Ideal mechanical advantage is the mechanical
advantage of a simple machine that does not take
friction into account.
• The ideal mechanical advantage of a lever is equal
to the distance from input force to fulcrum (dinput)
divided by the distance from output force to
fulcrum (doutput).
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Unit 2 Lesson 3 Machines
What are the three classes of levers?
• There are three classes of levers that differ based
on the positions of the fulcrum, the load, and the
input force.
• In a first-class lever, the fulcrum is between the
input force and the load.
• In a second-class lever, the load is between the
fulcrum and the input force.
• In a third-class lever, the input force is between
the fulcrum and the load.
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Unit 2 Lesson 3 Machines
What are the three classes of levers?
• Which is a first-class lever, which is a second-class
lever, and which is a third-class lever?
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Unit 2 Lesson 3 Machines
Turn, Turn, Turn
What is a wheel and axle?
• A wheel and axle is a simple machine that is
made of a wheel connected to a smaller cylindrical
object, the axle.
• The ideal mechanical advantage of a wheel and
axle equals the radius corresponding to the input
force (radiusinput) divided by the radius
corresponding to the output force (radiusoutput).
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Unit 2 Lesson 3 Machines
What is a wheel and axle?
• The radius of the wheel is always larger than the
radius of the axle. The mechanical advantage is
greater than one when the input force is applied
to the wheel. The mechanical advantage is less
than one when the input force is applied to the
axle.
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Unit 2 Lesson 3 Machines
What are the types of pulleys?
• A pulley is a simple machine that has a grooved
wheel that holds a rope or a cable. A load is
attached to one end of the rope, and an input
force is applied to the other end.
• There are three different types of pulleys.
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Unit 2 Lesson 3 Machines
What are the types of pulleys?
• A fixed pulley is attached to something that does
not move. It allows you to pull down on the rope
to lift the load up.
• The wheel of a movable pulley is attached to the
object being moved. One end of the rope is fixed.
You can pull on the other end of the rope to make
the wheel and load move along the rope.
• A block and tackle pulley is a pulley system made
by combining a fixed pulley and a movable pulley.
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Unit 2 Lesson 3 Machines
So Inclined
What are inclined planes?
• An inclined plane is a simple machine that is a
straight, slanted surface. A smaller input force is
needed to move an object using an inclined plane
than is needed to lift the object. However, the force
must be applied through a longer distance. So, the
amount of work done on the object is the same.
• The ideal mechanical advantage of an inclined
plane can be calculated by dividing the length of
the incline by the height that the load is lifted.
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Unit 2 Lesson 3 Machines
What are inclined planes?
• When you push something up a ramp, you are
using an inclined plane.
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Unit 2 Lesson 3 Machines
What are wedges?
• A wedge is a pair of inclined planes that move.
They have one thick end and one thin end.
Wedges are used to cut and split objects.
• The output force of the wedge is greater than the
input force, but the output force is applied
through a shorter distance.
• The longer and thinner the wedge is, the greater
its ideal mechanical advantage.
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Unit 2 Lesson 3 Machines
What are wedges?
• Chisels, ax heads, and knife blades are wedges.
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Unit 2 Lesson 3 Machines
What are screws?
• A screw is an inclined plane that is wrapped in a
spiral around a cylinder.
• When a screw is turned, a small force is applied
through the distance along the inclined plane of
the screw.
• The screw applies a large force through the short
distance it is pushed.
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Unit 2 Lesson 3 Machines
What are screws?
• The longer the spiral on a screw is and the closer
together the threads are, the greater the screw’s
mechanical advantage.
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