Getting Started --- Tuesday, Jan. 10, 2012

1) Find your new assigned seat by checking the lists posted on the cabinets.

2) Copy weekly assignments with due dates into your agenda.

3) Copy the Simple Machines Vocabulary into your journal on the next available page. Follow the instructions on your desk.

4) Tape the guided notes for the week into your journal after the vocabulary.

Use the iRespond system to complete the Simple Machines Pre-Test for Week One.

S8P3. Students will investigate relationship between force, mass, and the motion of objects.

c. Demonstrate the effect of simple machines (lever, inclined plane, pulley, wedge, screw, and wheel and axle) on work.

CONTENT STANDARD

1. Define work and power. 2. Identify joules and watts as units of

measurement for work and power.3. Distinguish between work as defined in

physics and work in everyday life.4. Identify work and non-work examples of

moving objects.5. Calculate work and power.6. Cite everyday examples of work and

power.

TODAY’S GOALS

What is the difference between scientific work and work in everyday

life?

ESSENTIAL QUESTION

Definition: The transfer of energy to an object by using a force that causes the object to move in the direction of the forceSimple Machine Vocabulary

Work is the transfer of energy through a distance!Work is measured in Joules (one Newton x one meter = one joule)What else have you learned about that is measured in joules?

Examples:

a) Picking up a stack of books

b) Pushing a lawn mower across the yard

Example #1: Using a 10 N force, you push a shopping cart 8 m. How much work do you do?

Find Work Formula W = F x d

Given: Sub & Solve:

Example #1: Using a 10 N force, you push a shopping cart 8 m. How much work do you do?

Find Work Formula W = F x d

Given: Sub & Solve:

F = 10 ND = 8 m

Example #1: Using a 10 N force, you push a shopping cart 8 m. How much work do you do?

Find Work Formula W = F x d

Given: Sub & Solve:

F = 10 ND = 8 m

W = 10 N x 8 mW = 80 N-mW = 80 joules

Look at the formula again.

1. What happens to the amount of work if you use more force?

2. What happens to the amount of work if you move an object a longer distance?

Example #2: Jill is putting books on a shelf that is 1.5 m high. Each book has a weight of 8 N. How much work is being done on each book?Find Work Formula W = F x d

Given: Sub & Solve:

F = 8 Nd = 1.5 m

W = 8 N x 1.5 mW = 12 joules

How would Example #2 change if you were given 8 kg instead of 8N?

kg is mass, not weight (the force of gravity)

You cannot use mass in the place of weight (a force)!!!

How would Example #2 change if you were given 8 kg instead of 8N?

You would need to change 8 kg (mass) into weight first!

To convert mass into its weight on Earth, multiply by 9.8 m/s2

Applying a force does not always result in work being done. Examples: a) Trying to push a car stuck in snow and ice is not work

b) Carrying a heavy book across the room is not work

Applying a force does not always result in work being done. WHY???In order for work to be done (energy transferred to the object), the object must move in the direction of the force

Power is the rate at which work is done.

Simple Machine Vocabulary

Formula:Power = Work = W = F x d Time t t

Example #3How much power does a person weighing 500 N need to climb a 3-m ladder in 5 seconds?

How much power does a person weighing 500 N need to climb a 3-m ladder in 5 seconds?Find ________ Formula ___________Given: Apply & Solve:

P = F x d/tPower

F = 500 Nd = 3 mt = 5 s

P = (500 N x 3 m) 5 s

P = 300 N-m/sP = 300 watts

Power is measured in watts, named for James Watt, who worked on the steam engineOne watt = one joule per second

A watt is pretty small – about equal to the power used to raise a glass of water from your knees to your mouth in one second.

The power of most household appliances is measured in kilowatts.

Remember kilo- represents 1000

Historically, power was provided by animals (i.e. horses)

As machines replaced horses, people naturally estimated the power of a machine by how many horses it could replace. Today’s engines are still rated in terms of horsepower.

What is the difference between scientific work and work in everyday

life?

ESSENTIAL QUESTIONREVISITED

Summarize!!!Write several sentences in your journal summarizing what you learned today about work and power.

The summary will be graded.

SIMPLE MACHINE PROJECT

Due WednesdayJan. 18th

HOMEWORK ZONE

Use the time remaining in class to begin working on Practice Sheet #16

Kagan FREEZEQuestion #1How does work transfer energy to an object?

Question #2What is the unit used to measure work?

Kagan FREEZEQuestion #3What does power measure?

Question #4What is the unit used to measure power?

Kagan FREEZEQuestion #5Give an example of work transferring energy to an object.

Question #6Give an example of power.