Work and Simple Machines

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Work and Simple Machines
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What is work?

• In science, the word work has a different meaning
  than you may be familiar with.
• The scientific definition of work is is the
  transfer of energy to an object by a force that
  makes an object move in the direction of the
  force.

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Work or Not?

• According to the scientific definition, which is
  work and which is not?
• a teacher lecturing to his class?
• a mouse pushing a piece of cheese across the
  floor?
• And Why?

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Whats work?

• A scientist delivers a speech to an audience of
  his peers.
• A body builder lifts 350 pounds above his head.
• A body builder is holding 350 pounds above his
  head.
• A father pushes a baby in a carriage.
• A student leans against the wall in the hallway
  while talking to a friend.

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Whats work?

• A scientist delivers a speech to an audience of
  his peers. No
• A body builder lifts 350 pounds above his head.
  Yes
• A body builder is holding a 350 pounds above his
  head. No
• A father pushes a baby in a carriage. Yes
• A student leans against the wall in the hallway
  while talking to a friend. No

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Formula for work

• Work Force x Distance
• The unit of force is newtons
• The unit of distance is meters
• The unit of work is newton-meters
• One newton-meter is equal to one joule
• So, the unit of work is a joule

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WFD

• Work Force x Distance
• Calculate If the people move concrete block 10
  meters with a force of 20 N, how much work has
  been done?

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WFD

• Work Force x Distance
• If the people move concrete block 10 meters
  with a force of 20 N, how much work has been
  done?
• 200 joules
• (W 20N x 10m)

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History of Work

• Before engines and motors were invented, people
  had to do things like lifting or pushing heavy
  loads by hand. Using an animal could help, but
  what they really needed were some clever ways to
  either make work easier or faster. So machines
  were created.

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What is a Machine?

• A machine is a device that makes doing something
  easier.
• For example, a snow shovel is used to move snow
  easier, compared to moving it with your hands.
• All machines make tasks easier, but they do not
  decrease the amount of work required.
• Instead, a machine changes the way in which the
  work is done.

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Simple Machines

• Ancient people invented simple machines that
  would help them overcome resistive forces and
  allow them to do the desired work against those
  forces.

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Simple Machines

• A machine is a device that helps make work easier
  to perform by accomplishing one or more of the
  following functions
• transferring a force from one place to another,
• changing the direction of a force,
• increasing the magnitude of a force, or
• increasing the distance or speed of a force.

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Mechanical Advantage

• It is useful to think about a machine in terms of
  the input force (the force you apply) and the
  output force (force which is applied to the
  task).
• When a machine takes a small input force and
  increases the magnitude of the output force, a
  mechanical advantage has been produced.

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Mechanical Advantage

• Mechanical advantage is the ratio of output force
  divided by input force. If the output force is
  bigger than the input force, a machine has a
  mechanical advantage greater than one.
• If a machine increases an input force of 10
  pounds to an output force of 100 pounds, the
  machine has a mechanical advantage (MA) of 10.
• In machines that increase distance instead of
  force, the MA is the ratio of the output distance
  and input distance.
• MA output/input

The mechanical advantage is three, which means it
is three times easier to move this load with a
wheelbarrow than it is by hand
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Types of Simple Machines

• The six simple machines are
• Lever
• Wheel and Axle
• Pulley
• Inclined Plane
• Wedge
• Screw

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The Lever

• A lever is a simple machine made with a straight
  bar that moves on a fixed point called a fulcrum.
• All levers have two parts, the arm and the
  fulcrum. The longer the lever is, the less force
  will be needed to move the load.
• The load and the force move in opposite
  directions.
• Notice that as the hammer is pulled down, the
  nail moves up.

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Examples of Levers
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Wheel and Axle

• A wheel and axle is made from a wheel that turns
  on a center post.
• The larger the wheel is, the less force will be
  needed to move the load.
• There are two parts to this simple machine, the
  wheel and the center post called the axle.
• The force moves in the same direction as the
  load.

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Examples of Wheels and Axles
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Pulleys

• A pulley is a wheel with a rope around it. The
  rope fits into the groove on the wheel. The
  larger the wheel is, the less force will be
  needed to move the load.
• There are two parts to a pulley, the wheel and
  the rope.
• The load and the force move in opposite
  directions. As the rope is pulled down, the flag
  goes up.

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Examples of Pulleys
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Inclined Plane

• Any slanted surface is an inclined plane.
• A ramp is the most common type.
• The longer the inclined plane is, the less force
  will be needed to move the load.
• The load and force move in the same direction.

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Examples of Inclined Planes
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Wedge

• The wedge is made by putting two inclined planes
  together. They come together to form a V-shape.
• A wedge may be used to lift or pry apart heavy
  objects. A wedge can also be used to stop an
  object from moving.
• The force and load move in different directions.
• As the force moves the ax down, the load (wood)
  breaks apart and falls to the sides.

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Examples of Wedges
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Screw

• The screw is an inclined plane that is wrapped
  around a center post.
• The longer the inclined plane is the closer the
  threads of the screw will be and the less force
  will be needed to move the load.
• A screw has two parts, the inclined plane and the
  center post.
• The force and the load move in the same
  direction.
• As the force pushed down on the screw, the screw
  goes down into the wood.

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Examples of Screws
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Compound Machines

• when two or more simple machines operate
  together.
• Complex machines perform a task.
• Examples include