FarleyPhysics.com

1. Work and Power Lecture and demonstration.

2. Examples

3. Do problems 21-26 on page 120.  For 26, remember that F is the force of gravity, or mg.

Work and pulleys

Use this simulation to do the following: http://www.compassproject.net/sims/pulley.html

1. With one pulley, set the distance to lift to 0.2 m and the load to 10 N.  Slowly raise the applied force until the mass starts to rise.  The applied force should be equal to the load for one pulley.  When the mass is lifted, calculate the Work done by the applied force (applied force times distance the applied force moves) and the work done on the mass (Load times distance mass moves).

2. Switch the pulley system to Single Movable and slowly raise the applied force until the mass starts to rise.  What applied force raises the weight with a single movable pulley?  What is the work done on the mass, and what is the work done by the applied force?

3. Switch the pulley system to Single Compound and slowly raise the applied force until the mass starts to rise.  What applied force raises the weight with two pulleys?  What is the work done on the mass, and what is the work done by the applied force?  NOTE: Turn on the switches to show Work on the side and you wont have to calculate it all the time!

4. Switch the pulley system to Double Compound and slowly raise the applied force until the mass starts to rise.  What applied force raises the weight with a double compound pulley?  What is the work done on the mass, and what is the work done by the applied force?

5. Switch the pulley system to Triple Compound and slowly raise the applied force until the mass starts to rise.  What applied force raises the weight with a triple compound pulley?  What is the work done on the mass, and what is the work done by the applied force?

6. Switch the pulley system to Quadruple Compound and slowly raise the applied force until the mass starts to rise.  What applied force raises the weight with a triple compound pulley?  What is the work done on the mass, and what is the work done by the applied force?

7. How does the amount of work change as you change the pulleys?  How does the amount of Force needed to lift a mass change as you change the pulleys?  How does the distance change that the force goes compared to the mass?

Extra: The number of pulleys does not always change the force needed to lift a mass.  If you look at the number of ropes that are actually lifting the mass, you can see what is most important.  Can you come up with a relationship between the force needed to lift a weight and the number of strings doing the lifting?

Work Experiment

Today you will study work.  For each question below, draw a picture showing what you are doing, write the question and answer as a statement.

1. Use the Force meter to weigh one of the carts.  Write this weight down.  This is the force that gravity pulls down on the cart.

2. Slowly and with constant speed, find the force needed to lift a cart from the floor to the top of your desk.  How does this force compare to the weight in step 1?  Do this a couple times to make sure of your numbers.  Write a statement that explains it.

3. Calculate the work you did in step 2.  Show your calculation and answer in the correct units

4. Calculate the potential energy gained by the cart from the floor to the top of the table.  Show your calculation and answer in the correct units.

5. Compare the work you did in step 3 and the potential energy that you calculated in #4.  Are they close?

6. Now prop a ramp up to make a ramp that goes from the floor to the top of the table.  Measure the Force needed to pull the cart up the ramp and calculate the work done.

7. Compare the compare the force needed to  pull the cart up the ramp with the force needed to lift it straight up.

8. Calculate the work done lifting the cart up the ramp and compare it to the work done lifting it straight up.  Are they close?  If they are not, where do you think the extra energy went?

9. Measure the force needed to pull the cart along the ramp while it is horizontal.  This is the frictional force needed to pull the cart.  Calculate the work done by friction and see if the work done by friction plus the work done pulling the cart up the ramp is equal to the work done lifting the cart straight up.

Quiz

Quiz!  No, just kidding.  We are going to have the quiz on Monday when all the Business Academy kids can take it.  We wouldn’t want to leave them out of the fun.  We are going to take a practice quiz.  Here it is:

Gravity and Rotational Motion Practice Quiz

1. If a spaceship with a mass of 2 x 104 kg travels 1m away from an asteroid with a mass of 3 X106 kg, what will the gravitational force be between them?

2. Two masses have a gravitational force of 500 N between them.  If one of the masses is increased by a factor of 2, what is the new gravitational force between them?

3. Two masses have a gravitational force of 400 N between them.  If the distance between them is doubled, what is the new gravitational force?

4. Two masses have a gravitational force of 1000 N between them.  If the distance between them is doubled and each mass is increased by a factor of two, what is the new gravitational force?

Fill in the blanks for the following:

5. All objects with ___________ or energy produce gravity.

6. Gravity is directly propotional to the product of  ___________________________

__________________________________________________________________

7. Gravity is inversely proportional to________________________________squared.

8. Which direction does the acceleration point during circular motion?____________________________________________________________

__________________________________________________________________

9. True or False? If an object moves in a circle at a constant speed, its velocity vector will be constant.   The statement is _____________.

10. You swing a mass on a string around your head.  Draw a picture showing the direction the mass will go if the string is cut.

11. For the picture below, draw velocity the velocity vectors of an object in circular motion at each dot.

1. Exponents the easy way.

2. Do problems 17-20 on page 180

Using the Gravitational equation with Scientific Notation.

1. Return Energy Quiz

2. Inputing scientific notation into your calculator and into a computer with examples

3. Do problems 15, 17, 18 on page 180 in the book.

Read pages 172-179 in the book, draw the six drawings on the pages in your notes along with a description of each drawing, answer questions 8-14 on page 180.

1. Finish problems from yesterday.  For each problem, draw a picture representing the masses with the size of the circles representing the mass and the distances between the objects proportional to the distance in the problem.  (30 min.)

2. Read pages 168-171 in the physics book, draw each drawing on the pages in your notes along with a sentence explaining what is in the drawing (there are six), and answer the review questions 1-7 on page 180.  Finish what you don’t complete for homework.

Gravitation

Use the gravitational force equation to calculate the following:

1. If a spaceship with a mass of 1 x 104 kg travels 1m away from an asteroid with a mass of 1 X107 kg, what will the gravitational force be between them? (7N)

2. If two masses, each with a mass of 1 x107 kg are 10m from each other, what will the gravitational force be between them? (70N)

Variing mass:

Answer the following questions and draw a picture for each with circles representing the masses and the mass inside the circle:

1. Two masses have a gravitational force of 100 N between them.  If one of the masses is increases by a factor of 2, what is the new gravitational force between them?

2. Two masses have a gravitational force of 100 N between them.  If one of the masses is increases by a factor of 4, what is the new gravitational force between them?

3. Two masses have a gravitational force of 100 N between them.  If one of the masses is increases by a factor of 10, what is the new gravitational force between them?

4. Two masses have a gravitational force of 100 N between them.  If one of the masses is increases by a factor of 25, what is the new gravitational force between them?

5. Two masses have a gravitational force of 100 N between them.  If each of the masses is increased by a factor of 10, what is the new gravitational force between them?

Variing distance:

1. Two masses have a gravitational force of 100 N between them.  If the distance between them is doubled, what is the new gravitational force?

2.  Two masses have a gravitational force of 100 N between them.  If the distance between them is tripled, what is the new gravitational force?

3.  Two masses have a gravitational force of 100 N between them.  If the distance between them is quadrupled, what is the new gravitational force?

Tricky problems:

4.  Two masses have a gravitational force of 100 N between them.  If the distance between them is halved (half of what it was), what is the new gravitational force?

5. What has more of an effect on the gravitational force, increasing the mass by a factor of 2 or increasing the distance by a factor of two?  Explain why.

6.  Two masses have a gravitational force of 100 N between them.  If the distance between them is doubled and each mass is increased by a factor of two, what is the new gravitational force?