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Day 2 |
Lab |
Day 4 |
Vocabulary Test
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a force acting through a distance.
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In Greek mythology, Atlas held the world on his shoulders. Did he do any work? |
For work to occur, a force must produce motion in the direction of the force.
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W = F d |
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The units of force are Newtons and the units of distance are meters. The answer is in Newton-Meters. These units are referred to as Joules.
Work and Energy 
are closely related, but not the same.
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Test Your Concept Understanding: 
- A 1000 N mountain climber scales a 100 m cliff. How much work is done?
- You are using 50 N of force to push an empty cart down the school hall. Your friend, who weighs 800 N, jumps on the cart and wants to be taken for a ride. You push your friend down the hall for 20 meters before being caught by the Principal. How much work did you do pushing your friend on the cart?
- The space shuttle is the most powerful machine ever built by man. Use information from
calculate the answers to the following questions. Show all the data and calculations.
- What is the total force, in Newtons, generated by all the space shuttle rocket engines at lift-off?
- What is the weight, in Newtons, of the space shuttle when it is loaded, fueled, and ready for launch?
- How much work is done at lift-off to raise the space shuttle past the top of the lightning rod on the shuttle's fixed service structure, FSS?
Day 2
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What is energy? |
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or Power = Force X Distance / Time P = F d / t |
In this equation, the units of work are Joules and the units of time are seconds. The answer is in Joules per second. These units are referred to as Watts.
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One Horsepower is equal to 745.56 Watts.
You have probably thought of Watts as a unit of electricity, something related to a light bulb. Also, you might have thought of power in terms of how many horsepower a car engine can produce. Both of these ideas are correct. The number of Watts marked on light bulbs tells you how much work the bulb does in a period of time - that is power. The unit "horsepower" is an English System unit for power.
This assignment must be turned in by the end of class today to receive credit.
Scoring criteria
- Find out how horsepower works
- James Watt first described "horsepower". How many "foot-pounds per minute" is equal to one horsepower?
- One horsepower is equal to how many BTU's?
- Given the following information:
| Equations | Conversions |
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Does a machine produce more work than is put into it? |
Mechanical Engineer |
Machines make work easier by changing the size or direction of a force.
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2 forces are always involved when using a machine.
Work is done to a machine as well as by a machine.
When using a machine, distances are not the same.
Mechanical Advantage: the number of times a machine multiplies the effort force.
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MA = FR / FE |
Efficiency: a comparison of work output to work input.
Work output is never greater than work input.
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Efficiency = WO / WI X 100 |
Efficiency is always expressed as a percentage.
Test Your Concept Understanding:
- What does friction do to the efficiency of a machine?
- You use a pair of pliers to crack a pecan. It takes 1200 N of resistance force to crack the pecan, but you only exert 400 N of effort force with your hand on the pliers. What is the mechanical advantage of the pliers?
- Think of pliers as a pair of first-class levers.
Work Practice Problem Answers:
W = F d
Power Practice Problem Answers:
2000 Watts / 1000W/kW = 2 kilowatts
Atlas did no work by just holding up the world.
W = (800N) (40m)
W = 32000 Joules
Weight = (60Kg) (9.8m/s2)
Weight = 590N
W = (590N) (10m)
W = 5900 Joules
P = 4000 J / 5 s
P = 800 Watts
P = (1000N) (20m) / 10s
P = 2000 Watts
