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PPT – Energy, Work, and Simple Machines PowerPoint presentation | free to download - id: 78b9b0-MjE5M

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Chapter 10

- Energy, Work, and Simple Machines

10.1 Energy and Work

- Energy is the ability to produce change in itself

or the environment. - Energy of Motion
- vf2 vi2 2ad
- Rearranging
- vf2 - vi2 2ad
- Substituting Newtons second law
- vf2 - vi2 2Fd/m

- Multiply both sides by ½ m
- ½ mvf2 ½ mvi2 Fd
- Kinetic energy
- KE ½ mv2
- Work-Energy Theorem
- ?KE W
- When work is done on an object, a change in

kinetic energy results.

- Work
- Through the process of doing work, energy can

transfer from the environment to the object and

back again! - The equation for work is
- W Fd
- For constant forces in the direction of the

motion. - Unit of work is the joule (J)

- Constant force at an angle
- Work (angle between force and displacement).
- W Fd cos ?

- Power
- The rate at which work is done
- P W/t
- Power is measured in watts (joule/second)

PSS

- Sketch the problem.
- Establish a coordinate system
- Draw a vector diagram.
- List known and unknowns.
- Use the basic equation for work when a constant

force is exerted in the same direction as the

displacement. Or the equation W Fd cos ? which

will work in all situations.

- Use the work-energy theorem to determine the

change in energy of the system. - Use work and time to find power.
- Check your answer.

10.2 Machines

- Simple and Compound Machines
- The output work can never be greater than the

input work - The machine simply aids in the transfer of

energy. - Mechanical Advantage
- The force you exert on a machine is called the

effort force Fe - The force exerted by the machine is called the

resistance force Fr

- The ratio of resistance force to effort force, is

called the mechanical advantage. - Mechanical Advantage
- MA Fr / Fe
- This equation can be rewritten using the

definition of work - Wo Wi or
- Frdr Fede
- Rearranging this gives
- Fr/Fe de/dr

- We know that the mechanical advantage is given by

MA Fr/Fe - For an ideal machine, MA de/dr
- Because this equation is characteristic of an

ideal machine, the mechanical advantage is called

the Ideal Mechanical Advantage - IMA de/dr

- Efficiency
- The efficiency of a machine is defined as the

ratio of output work to input work. - Efficiency () Wo/Wi X 100
- An ideal machine has equal output and input work

and the efficiency is 100. - In terms of mechanical advantage and ideal

machine advantage - Efficiency () (Fr/Fe)/(de/dr) X 100
- Efficiency () MA / IMA X 100

- Simple machines
- Most simple machines are combinations of one or

more of the six simple machines. - They are the lever, pulley, wheel and axel,

inclined plane, wedge, and screw. - The IMA of all machines is the ratio of distances

moved.

- Compound machines
- A compound machine consists of two or more simple

machines linked so that the resistance force of

one machine becomes the effort force of the

second. - The mechanical advantage of a compound machine is

the product of the mechanical advantage of the

simple machines it is made up of. - MA MA machine 1 X MA machine 2