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6.8 Power -- Part 1

- The bar charts can be used to apply energy and momentum constancy.

- It's very fast but reasonable for a bul et to fire from a gun.

- Determine the initial energy of the bullet, the final potential energy of the block-bul et system, and the increase in internal energy of the system.

- The energy is converted at a faster rate when you run up the stairs.

- The watt is the SI unit of power.

- A cyclist in good shape pedaling at moderate speed will convert about 400-500 J of internal chemical energy each second.

- Power can be expressed inhp: 1hp is 746 W.

- Horsepower is used to describe the power rating of machines.
- The internal energy of the fuel is converted into other forms of energy at a rate of 50 * 746 W.

- The barbell has a dead lift on it.
- She lifts a bar that is moving at a smal constant velocity, the external force from the floor to just below her waist is very nearly constant.

- The process can be represented with an energy bar chart.

- The process is shown below.
- The barbel and Earth are the system.
- The initial state of this process is the most important.
- The last state is after she finishes lifting.

- This is a good power for lifting a barbell.
- If you use an exercise machine that displays the power output, compare what you can achieve to this number.

- Lifting assume that Xueli lifts the same barbell from her shoulders to above her head.

- Estimate the power of the process.
- The pro arm is 49 cm and her energy is zero.
- She needs 1.0 s to lift cess.
- She works at the bar.

- N pointing at the direction of the car.

- 25hp is a relatively small power.

- Determine the power of Jim's erblades on a smooth linoleum floor.

- When an object is close to Earth's surface, this expression is valid.

- Imagine if a space elevator was built to transport supplies from the surface of Earth to the International Space Station.

- The supplies leave the surface.
- The International Space Station is chosen via a space Earth and supplies.
- We will lift the supplies.
- The only type of energy force diagram that we can keep track of is gravitational potential energy.

- A complex math ematical procedure is needed to determine the work done by a variable force.

- The International Space Station is not from the center of Earth.
- Check to see if the equation makes sense.

- The initial state and the final state are both described in two quantities.

- We can use it.
- If we know the mass of any two spherical or point-like objects, we can see a bar chart.

- There was positive work done on the system by the cable.
- The final potential energy of the system is zero.

- The potential energy is zero when the object is far away.

- When the object is far from Earth, the negative potential energy is zero.

- The initial state is when the object is close to Earth and the final state is far away.

- The amount of work needed to raise 1000 kilograms of supplies to the International Space Station can now be determined.

- Had we used our original expression, we could have calculated what this would have been.
- The surface of Earth has a zero level.

- The bars on which the best Olympic high jumpers leap are about 8 feet above Earth's surface.
- When leaving the ground, we can estimate a jumper's speed.
- The zero level of gravitational potential energy at ground level was chosen as the system.
- The potential energy of the system is converted as the jumper leaves the ground.

- M is 1.6 N>kg.

- We draw a sketch first.
- The system to choose is the process.
- The planet will be the initial state.

- The constant is 6.67.

- The above equation can be used to determine the escape speed.

- In the initial state, the system has 2370 m>s of energy.
- The potential energy for Earth is zero in the final state.

- The bar chart shows the Sun's mass and the work-energy equation.

- Something amazing is suggested by the escape Equation (6.12).
- The es mass of the escaping object could be made large if the mass speed did not depend on the star or planet.
- Light leaving the star's surface wouldn't be fast enough to leave Earth.
- Why don't you escape the star?
- The star would be very dark.

- Imagine if Earth began to shrink so that it was compressed into a smaller volume.

- It's hard to imagine Earth being compressed to the size of a marble.
- The mass would be the same, but it would be very dense.
- The first equation was created by astronomer Pierre-Simon Laplace, who used classical mechanics to predict the presence of dark stars.

How small would our Sun need to be in order to return to this question in later chapters?

- The mass of the Sun needs to be shrunk to 1030 kilograms.
- All we need to do is use the book.

- We've been talking about objects that are larger than light.
- Physicists used to think that the force of gravity on light would always be zero.
- Albert Einstein's theory of general relativity improved greatly at the beginning of the 20th century.
- Light is affected by gravity.
- The size of a black hole is predicted by the theory.

- The energy potential of the Sun and Earth is negative in this section.

- It is a number.

- It is a number.

- The faces of the system objects rub against each other as the internal energy of the system changes.

- External forces can change the energy of a system.

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