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.

Work = Force X Distance W = F d

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.

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 Kennedy Space Center Space Shuttle Clickable Map Kennedy Space Center's Science Homepage 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

What is energy?

Power = Work / Time 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.

Practice Problems: A machine produces 4000 Joules of work in 5 seconds. How much power does the machine produce? A box that weighs 1000 Newtons is lifted a distance of 20 meters in 10 seconds. How many kilowatts of power are produced?



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 (P = work / time).

In-class Assignment 252:
This assignment must be turned in by the end of class today to receive credit.
Scoring criteria

1. Find out how horsepower works then answer the following:
   1. James Watt first described "horsepower". How many "foot-pounds per minute" is equal to one horsepower?
   2. One horsepower is equal to how many BTU's?

2. Given the following information:

Equations	Conversions
Weight = (mass) (acceleration of gravity) = (kilograms) (10 m/s2 = Newtons Work = (force) (distance) = (Newtons) (meters) = joules Power = work / time = joules / seconds = Watts	one pound = 0.5 kilogram   one foot = 0.3 meters   one horsepower = 746 Watts

1. A person weighing 150 pounds is lifted 200 feet by an elevator. Calculate the work done by the elevator in "foot-pounds".
2. Calculate the work done by the elevator in joules.
3. If the elevator lifts the person in 20 seconds, how many Watts of power are produced?
4. Convert the Watts to horsepower.

Day 4

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.

2 forces are always involved when using a machine.

• Effort Force - F_E - the force applied to a machine.
• Resistance Force - F_R -the force applied by a machine.

• Work Input - W_I - the work done on a machine.
• Work Output - W_O - the work done by a machine.

• Effort Distance - d_E - the distance through which the machine moves.
• Resistance Distance - d_R - the distance the object moves.

Mechanical Advantage: the number of times a machine multiplies the effort force.

Mechanical Advantage = Resistance Force / Effort Force MA = FR / FE

• MA is greater than 1 - the machine is used to increase the effort force.
• MA is equal to 1 - the machine is used to change the direction of the effort force.
• MA is less than 1 - the machine is used to increase the distance an object moves or the speed at which it moves.

Efficiency: a comparison of work output to work input.

Work output is never greater than work input.

Efficiency = Work Output / Work Input X 100 Efficiency = WO / WI X 100

Efficiency is always expressed as a percentage.

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. The fulcrum about which the levers turn is located at point B. The lever arm represented by the line AB is 6 cm long. The lever arm represented by line BC is 3 cm long. What is the mechanical advantage of this set of pliers?

Physical Science

Work Practice Problem Answers:

1. W = F d
   W = (800N) (40m)
   W = 32000 Joules

2. Weight = m g
   Weight = (60Kg) (9.8m/s²)
   Weight = 590N

   W = F d
   W = (590N) (10m)
   W = 5900 Joules

Power Practice Problem Answers:

1. P = W / t
   P = 4000 J / 5 s
   P = 800 Watts

2. P = W/t = Fd/t
   P = (1000N) (20m) / 10s
   P = 2000 Watts

   2000 Watts / 1000W/kW = 2 kilowatts

Atlas did no work by just holding up the world.

Energy is the ability to do work.

A machine can never produce more work than is put into it.