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History Of Energy

- From Greek energeia meaning “activity.”
- Not part of original Newtonian mechanics.
- Introduced into physics by Helmholtz in 1847.

Defining Property of Energy

The total energy of an isolated system does not change with time.

Kinetic energy

- If an object is moving then it is capable of doing work.
- The object has energy of motion (kinetic energy).
- The kinetic Energy of an object is dependant on the amount of mass and sped of the object and its is equal to half of the mass x speed squared
- Kinetic Energy= .5 (MassxSpeedSquared)

Potential Energy

- An object can have energy due to its position this is called potential energy!
- At a resting state the object only has potential to do work.
- A good example is an object like a compressed spring that has the “potential” to do work (spring upwards).
- Potential Energy= Weight x Height

Work

- Quantity of force x Distance= Work
- An example of this is if you have a bowling ball and you want to shoot it up in the air 2 ft., it wont require nearly as much work as trying to shoot a bowling ball 20 ft.
- Work occurs when one moves an object against the Earths gravitational pull.
- The heavier the load requires more work depending on the distance the

The Measurement of “Work”

- When the measurement of force you combine the unit of force (Newton) with the units of distance (Meters)
- MxN=Joules
- 1 Joule of work is done when one Newton of force is exerted over the distance of one meter.

Power

- Power= Work done/Time interval
- An example of when you need to think of power is when you carry a load up stairs, you do the same amount of work whether you run up the stairs or walk up the stair. Than why are you more tiered when you run up the stairs in a few seconds rather than walk in a few minutes?
- This is the thought of work done over time or Power.

Power (Continued)

- Power is simply energy exchanged per unit time, or how fast you get work done (Watts = Joules/sec)
- One horsepower = 745 W
- Perform 100 J of work in 1 s, and call it 100 W
- Run upstairs, raising your 70 kg (700 N) mass 3 m (2,100 J) in 3 seconds 700 W output!
- Shuttle puts out a few GW (gigawatts, or 109 W) of power!

Energy is Conserved

- The total energy (in all forms) in a “closed” system remains constant
- This is one of nature’s “conservation laws”
- Conservation applies to:
- Energy (includes mass via E = mc2)
- Momentum
- Angular Momentum
- Electric Charge
- Conservation laws are fundamental in physics, and stem from symmetries in our space and time
- Emmy Noether formulated this deep connection
- cedar.evansville.edu/~ck6/bstud/noether.html

Machines

- A device by which a small force applied at convenient point can be used to overcome a large force at some other point.The force overcome by a machine is many times greater than the input force, the energy or work output can never be greater than the input energy or work. In
- Work input=Work output

Types of Machines

- 3 Types of machines
- The lever, the pulley, and the inclined plane
- Also known as wheel and axle, the wedge, and the screw are modifications of the three simple machines.

Pulleys

- Two types of pulleys
- Fixed pulleys
- Moveable pulleys
- Are simple machines that consist of a rope that slides around a disk, called a block. Their main function is to change the direction of the tension force in a rope.

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