In class notes quiz, Chapter 8 1. Work is defined as _____________.

1. In class notes quiz, Chapter 8 1. Work is defined as _____________. 2. We do work when we ________________________. 3. The unit of measurement for work is a ____________. 4. __________ is the rate at which work is done. 5. When holding a heavy barbell over your head you are doing work. T or F 6. ____________ is what enables something to do work. 7. A stretched rubber band has ______________________. 8. _______________ is the energy of motion. 9. If you double the speed of your car, you will _____________ your stopping distance when you lock-up the brakes. 10. The Law of Conservation of Energy says: Energy cannot be _________ or ____________. Bonus: Two simple machines are a _________ and a _____________.

5. Energy is only observed when something is happening - when it is being transformed or transferred When energy of an object changes - work is done on that object. Work = Force x distance Work require - application of a force -movement of something by that force -unit of work is the Joule (Newton*meter)

6. Power - rate that work is done Power = Work / time - unit of power is the watt 1 watt = 1 Joule / 1 second Energy is what enables an object to do work Mechanical Energy - energy due to position of an object or movement of an object - comes in 2 forms: potential, kinetic or a combination of the two

7. Potential energy - stored energy - potential energy due to positions above the Earth is gravitational potential energy - gravitational potential energy equals the work done to lift the object (Weight x height) PE = mgh - depends on the final height above the ground, not on the path taken to get there

8. Kinetic energy - energy of motion - a moving object is capable of doing work KE = 1/2 mv2 - is equal to the work needed to bring the object from its given speed to rest Fd = 1/2 mv2 - note that speed is squared in the formula, so doubling the speed, quadruples the kinetic energy - work changes kinetic energy - no change in kinetic energy no work is done work-energy theorem Work = change in Energy

9. Law of Conservation of Energy Energy cannot be created or destroyed. It can be transformed from one form to another but the total amount of energy never changes. Machine - a device used to multiple forces or change the direction of forces - machines must follow the Law of the Conservation of Energy work input = work output - no machine can multiply work or energy

10. Lever - changes the direction of a force - when the fulcrum is close to the load a lever will multiply force mechanical advantage = output force / input force Pulley - a kind of lever used to change the direction of a force - mechanical advantage for a simple pulley system in the same as the number of strands of rope that actually support the load

11. Ideal machines have 100% efficiency. - some energy is lost to heat - lower the efficiency, greater the loss of energy to heat Efficiency = useful work output total work output Efficiency = actual mechanical advantage theoretical mechanical advantage Efficiency is always a fraction less than 1