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Transcript of Laws of Motion and Energy Chapter Six: Energy and Machines 6.1 Energy and Conservation of Energy 6.2...
![Page 1: Laws of Motion and Energy Chapter Six: Energy and Machines 6.1 Energy and Conservation of Energy 6.2 Work and Power 6.3 Simple Machines.](https://reader035.fdocuments.in/reader035/viewer/2022070306/5517fb8a550346a2228b4a37/html5/thumbnails/1.jpg)
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Laws of Motion and Energy
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Chapter Six: Energy and Machines
• 6.1 Energy and Conservation of Energy
• 6.2 Work and Power
• 6.3 Simple Machines
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Investigation 6B
• How do simple machines operate?
Force, Work and Machines
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6.3 Simple Machines
• A machine is a device, like a bicycle, with moving parts that work together to accomplish a task.
What kinds of energy are needed to make this machine work?
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6.3 Input and output• To understand how a machine works, think
about input and output. • The input includes everything you do to make
the machine work.• The output is what the machine does for you.
Input
Output
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6.3 Input and output• Input can be forces, energy, or power
supplied to make a machine work.
• Output is the forces, energy, or power provided by the machine.
ForcesEnergyPower
ForcesEnergyPower
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6.3 Simple Machines• A simple machine is an unpowered
mechanical device, such as a lever. • Some other simple machines are a wheel and
axle, ropes and pulleys, gears, and a ramp.
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6.3 Input and output• With a lever, the input force (also called
the effort) is the force you apply.
• The output force is the force exerted on the load you are lifting.
Input
Output
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6.3 Simple machines
• One person can easily lift an elephant with a properly designed system of ropes and pulleys.
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6.3 Work and energy• The output work done by a simple machine can
never exceed the input work done on the machine.
• Friction always converts some of the input work to heat and wear, so the output work is always less than the input work.
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6.3 Real machines and efficiency
• The efficiency of a machine is the ratio of work output to work input.
Can you calculate the efficiency of this machine?
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6.3 Real machines and efficiency
• Efficiency is usually expressed in percent.• Because some friction is always present, 100%
efficient machines are impossible.• An important way to increase the efficiency of a
machine is to reduce friction. – Ball bearings and oil reduce rolling friction. – Slippery materials such as TeflonTM reduce sliding
friction. – Designing a car with a streamlined shape reduces air
friction.
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6.3 Real machines and efficiency
• Cars are not very efficient at using the energy in gasoline.
• Only 13 % of the energy in a gallon of gas is transformed into output work.
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6.3 Mechanical advantage and levers
• You can make a lever by balancing a board on a log.
• Pushing down on one end of the board lifts a load on the other end of the board.
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6.3 Mechanical advantage and levers
• All levers include a stiff structure that rotates around a fixed point called the fulcrum.
• Levers are found in many common machines.
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6.3 Mechanical advantage and levers
• Mechanical advantage is the ratio of output force divided by input force.
• The input and output forces are different if the fulcrum is not in the center.
This lever has a mechanical advantage of 3.
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6.3 Ropes and pulleys
• Ropes and strings carry tension forces along their length.
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6.3 Ropes and pulleys
• The mechanical advantage of a pulley system depends on the number of strands of rope directly supporting the load.
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6.3 Ropes and pulleys
• There are 2 strands of rope supporting this load, so the load feels 2 times your input force.
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6.3 Ropes and pulleys
• What is the mechanical advantage of a pulley with three strings?
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6.3 Gears, ramps and screws
• Gears allow rotating speeds to change while power stays constant.
• The rule for how two gears turn depends on the numbers of teeth on each.
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6.3 Gears, ramps and screws• A ramp allows you to
raise a heavy cart with less force than you would need to lift it straight up.
• Ramps reduce the input force by increasing the distance over which the input force acts.
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6.3 Gears, ramps and screws
• A screw is a simple machine that turns rotating motion into linear motion.
• A screw works just like a ramp that curves as it gets higher.
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Technology Connection
A Mighty Energizing Wind
• There is a new kind of farm that is unlike any other – it doesn’t produce food - it produces energy from wind.
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Chapter Activity
• Rube Goldberg is well known for creating fun illustrations that show how many simple steps can work together to accomplish something.
• For this activity, you will design and build a multi-step device that will pop a balloon.
Pop Goes the Balloon