Notes 5-2 Introduction to Machines

  • Objective: Explain how machines make work easier.
  • Objective: Calculate mechanical advantage and efficiency.

CLE 3202.4.3 Demonstrate the relationship among work, power, and machines.

A. Using Machines

  1. A machine is device that ______.
  2. Machines can be ______.
  3. Some, like knives, scissors, and doorknobs, are used everyday to make doing work easier.

4. Machines make work easier by:

a.increasing the ______that can be applied to an object.

b. increasing the ______over which a ______

can be applied.

c. changing the ______of an applied force.

  • A car jack is an example of a machine that increases an applied force.
  • The upward force exerted by the jack is greater than the downward force you exert on the handle.
  • The jack increases the applied force, but doesn’t increase the work done.
  1. Increasing ______reduces the amount of force needed to do the work.
  1. Same amount of workcan be done by applying a small force over a long ______as can be done applying a large force

over a ______distance, since Work = ______

B. Changing Direction

  1. Some machines ______the ______of the ______you apply.
  2. The wedge-shaped blade of an ax is one example.

The blade changes the downward force into a horizontal force that splits the wood apart.

C. Forces

______are involved when a machine is used to do work.

  1. ______
  2. force applied______the machine
  3. “what ______”
  4. ______
  5. force applied _____ the machine to overcome the resistance
  6. “what the ______”

D. Work

Two kinds of work need to be considered.

  1. The work ______on a machine is called the ______(_____).
  2. The work done ______the machine is called the ______

Work Input (Win)

workdone ______a machine WorkOutput (Wout)

work done ______a machine

E. Conserving Energy

1. A machine ______, so Wout is ______greater than Win.

2. When a machine is used, some of the energy transferred changes to heat due to ______.

3. The energy that changes to heat cannot be used to do work, so Wout is always ______than Win.

F. Ideal Machine

In an ideal machine...One in which there was ______.

But in the real world…some energy is lost as ______

G. Mechanical Advantage

•Mechanical Advantage ______

•______

H. Ideal Mechanical Advantage

  1. The mechanical advantage of a machine ______is called the ideal mechanical advantage, or ______.

Mechanical Advantage Problems:

A worker applies an effort force of 20 N to open a window with a resistance force of 500 N. What is the crowbar’s MA?

Given:Work:

Find the effort force needed to lift a 2000 N rock using a jack with a mechanical advantage of 10.

Given:Work:

I. Efficiency

  1. Efficiency is a measure of how much work put into a machine is ______into useful ______by the machine.
  2. A machine with high efficiency produces ______from friction so more of the input work is changed to useful output work.
  3. ______, such as oil or grease, can make machines more efficient by reducing friction.

4. A lubricant fills in the gaps between the surfaces, enabling the surfaces to slide past each other more easily.

A worker exerts a force of 500 N to push a 1500 N sofa 4.0 m along a ramp that is 1.0 m high. What is the ramp’s efficiency?

Given:Work:

Questions:

Why is a machine’s efficiency less than 100%?

Some energy is ______due to ______.

Question 1

What do a knife, a doorknob, and a car jack have in common?

Answer: They are all machines, devices that ______

Question 2

When a machine is used to do work, the force that is applied to the machine is the ______.

  1. fulcrum
  2. effort force
  3. mechanical advantage
  4. resistance force

Question 3

What is the effect of increasing a machine’s efficiency?

Answer: Increasing efficiency increases the amount of ______energy converted to useful ______.