Learning Objective: Students will be able to explain how machines help to make work easier by calculating mechanical advantage to examine

the relationship between the output force and input force.

POD:

• Machine – a device that makes doing work ___________________

• Input force: the force that you _________________ on a machine

• Output force: the force that

the___________________ applies

POD:

• Machine – a device that makes doing work __easier____

• Input force: the force that you __exert_________ on a machine

• Output force: the force that the

__machine________ applies

• Mechanical advantage: the number of times a machine increases the input force

• MA = output force (in Newtons) / input force (in Newtons)

• MA = Fout / Fin

* Output WORK is never greater than input work, BUT output FORCE can be greater than input force

Solution Steps – Ask Yourself:

• What do I know? • What do I need to find out? • What procedure am I going to use?• How can I check my work? * Notice when determining mechanical

advantage, there is NO UNIT.

Problem 1

To open a bottle, you apply a force of 50 N to the bottle opener. The bottle opener applies a force of 775 N to the bottle cap. What is the mechanical advantage of the bottle opener?

Problem 1 Answer

To open a bottle, you apply a force of 50 N to the bottle opener. The bottle opener applies a force of 775 N to the bottle cap. What is the mechanical advantage of the bottle opener?

• Output Force / Input Force = Mechanical Advantage

• 775N / 50N = MA• MA = 15.5

Problem 2

• To crack a pecan, you apply a force of 50 N to the nutcracker. The nutcracker applies a force of 150 N to the pecan. What is the mechanical advantage of the nutcracker?

Problem 2 Answer

• To crack a pecan, you apply a force of 50 N to the nutcracker. The nutcracker applies a force of 150 N to the pecan. What is the mechanical advantage of the nutcracker?

• MA = 3

Problem 3

• To pull a weed out of a garden, you can apply a force of 50 N to the shovel. The shovel applies a force of 10 N to the weed. What is the MA of the shovel?

Problem 3 Answer

• To pull a weed out of a garden, you can apply a force of 50 N to the shovel. The shovel applies a force of 10 N to the weed. What is the MA of the shovel?

• MA = 1/5 = .2

Problem 4

To pry a nail out of a wall, you can apply a force of 25 N to a hammer. The hammer applies a force of 650 N to the nail. What is the MA of the hammer?

Problem 4 Answer

To pry a nail out of a wall, you can apply a force of 25 N to a hammer. The hammer applies a force of 650 N to the nail. What is the MA of the hammer?

MA = 26

Problem 5

• The mechanical advantage of a rope is 7. To lift a block on a movable pulley, you can apply a force of 100 N to a rope. How much force does the rope apply?

Problem 5 Answer

• The mechanical advantage of a rope is 7. To lift a block on a movable pulley, you can apply a force of 100 N to a rope. How much force does the rope apply?

Output Force = 700 N

Problem 6

• You are trying to pull apart two pieces of wood using a lever. The lever applies a force of 640 N to the weed with a mechanical advantage of 32. How much force must you apply to the lever?

Problem 6 Answer

• You are trying to pull apart two pieces of wood using a lever. The lever applies a force of 640 N to the weed with a mechanical advantage of 32. How much force must you apply to the lever?

Input Force = 20 N

Problem 7

• A wedge has a mechanical advantage of 20. To lift a refrigerator, you can apply a force of 30 N to a wedge. How much force does the wedge apply?

Problem 7 Answer

• A wedge has a mechanical advantage of 20. To lift a refrigerator, you can apply a force of 30 N to a wedge. How much force does the wedge apply?

• Output Force = 600 N

Problem 8

• The output work of a machine is 35J. The input work is 70J. What is the efficiency of the machine?

Problem 8 Answer

• The output work of a machine is 35J. The input work is 70J. What is the efficiency of the machine?

Efficiency = 50%

Problem 9

The output work of a machine is 25 J. The efficiency of the machine is 100%. What is the input work?

Problem 10

• What type of machine is the one from the previous question?

Problem 10 Answer

• What type of machine is the one from the previous question?

• It is an ideal machine (100% efficient)