Lesson_22 Pulleys

Simple Machines: Pulleys

Pulley

3 types of pulleys

• _{Fixed pulley}

• _{Movable pulley}

Fixed Pulley

-Pulley is fastened securely -1st class lever

- Changes the direction of force

10 lb

10 lb

10 lb

5 lb 5 lb Movable Pulley

-Pulley moves as effort force is applied -2nd class lever

-Force directions stay constant

Pulleys In Combination

Pulley Demonstration with Test Boards

STEP 1:

Pulley Demonstration with Test Boards

STEP 2:

Pulley Demonstration with Test Boards

STEP 3:

Hang a 4’ string around the pulley. On the left end of the string hook on a 1.25 lb weight.

On the right end of the string hook on the

Pulley Demonstration with Test Boards

STEP 4:

Pull down on the force gauge so that it moves the weight up 2 inches (resultant distance). Record the following in Data Table 1:

•_{Effort force - the force that is}

needed to pull up the weight

•_{Effort distance - the distance}

Pulley Demonstration with Test Boards

STEP 5:

Repeat steps 3 & 4

with the 2.5 lb weight.

STEP 6:

Pulley Demonstration with Test Boards

STEP 7:

Set up a 4” support bolt at (12, 40) and (18, 40).

STEP 8:

Pulley Demonstration with Test Boards

STEP 9:

Create a movable pulley by assembling the following pieces together:

2” bolt > one end of 1’ string loop > hex nut >

Pulley Demonstration with Test Boards

STEP 10:

Hang one end of the string used in step 3 on the support bolt at (12, 40), thread the string around the movable pulley, and hang the

other end of the string on the force gauge hook.

Pulley Demonstration with Test Boards

STEP 12:

Hook the 1.25 lb weight onto the 1’ string on the moveable pulley

STEP 13:

Pulley Demonstration with Test Boards

STEP 14:

Pull up on the force gauge so that it moves the weight up 2 inches (resultant distance). Record the following in Data Table 2:

•_{Effort force - the force that is needed to pull}

up the weight

•_{Effort distance - the distance that the force}

gauge moved

STEP 15:

Repeat steps 12 – 14 with the 2. 5 lb weight.

STEP 16:

Pulley Demonstration with Test Boards

STEP 17:

Rest the force gauge on the support bolt at (18, 40).

STEP 18:

Move the end of the 4’ string from the support bolt at (12, 40) and place it so that it is on the bolt that holds the fixed pulley at (6, 40).

STEP 19:

Pulley Demonstration with Test Boards

STEP 20:

•_{Pull on the force gauge so that it moves the}

weight up 2 inches (resultant distance). Record the following in Data Table 3:

•_{Effort force - the force that is needed to pull}

up the weight

•_{Effort distance - the distance that the force}

gauge moved

STEP 21:

Repeat step 20 with the 2. 5 lb weight.

STEP 22:

For each pulley, was the effort force

the same as the resultant force?

For each pulley, was the effort

distance the same as the resultant

When would a fixed pulley be useful?

When would a moveable pulley be useful?

Conclusion

Was your hypothesis “supported” or “not supported”?

Did you get the results you expected? Why or why not?

Were there any mistakes/errors in your experiment; if so how might it have affected your results?

How could you use what you learned from your experiment?

Simple Machines: Pulleys

Mechanical Advantage

The advantage that the machine gives to the user

If the Mechanical Advantage is:

> 1 less force is required from the user < 1 more force is required from the user = 1 the same amount of force is required

When would we want a mechanical

advantage > 1?

When would we want a mechanical

advantage < 1?

When would we want a mechanical

advantage = 1?

Fixed Pulley

-Pulley is fastened securely -1st class lever

-Changes the direction of force -The mechanical advantage is 1

10 lb

10 lb

10 lb

5 lb 5 lb Movable Pulley

-Pulley moves as effort force is applied -2nd class lever

-Force directions stay constant

-The mechanical advantage is 2

Can we calculate the mechanical

Lever

Inclined Plane

The maximum weight allowed on the roller coaster is 3,000 pounds. The force that is needed to push the maximum weight up the

inclined plane is 2,400 pounds.

What is the MA using distance?

What is the MA using force?

Wheel and Axle

What is the MA using distance? What is the MA using force?

Ǿ12 in. Ǿ24 in.

100 lbs

How does this help an engineer?

A grocery store is raised up above the parking lot. The civil engineer needs to make a ramp to allow

customers to get in an out of the store with all of their groceries. Is the design below acceptable to push a full cart of 150 pounds? Explain why or why not.

5 ft