Section 1 Work and Machines

Essential Questions What is work? How can work be calculated when force and motion are parallel to each other? How do machines make doing work easier? What are mechanical advantage and efficiency?

New Vocabulary work compound machine machine efficiency simple machine mechanical advantage

Definition of Work To many people, the word work means something that people do to earn money. fixing cars designing Web sites. The word work might also mean exerting a force with muscles. Work is a force applied through a distance. W= applied force x distance W = F x d In order to do work on an object, you must move it a distance. Force and distance must be parallel. Purestock/age fotostock

Work , Force and Distance Work is measured in Joules (J) A Joule is a Newton x a meter or a Nm Work always involves a transfer of energy. Sample work problem: A box is pushed across the floor with a force of 100 Newtons and moves a distance of 10 meters. How much work is done in moving the couch? W = f x d W = ? F = 100N d = 10 m W = 100N x 10m W W = 1000J W F D

Machines A machine is a device that changes the force or increases the motion from work. They cannot increase work done on an object. Imagine trying to lift a grand piano. What could you use to help? Push the piano up a ramp Lift the piano with a pulley system In both cases, you use a machine to change the force on the piano.

Machines The six types of simple machines are lever, wheel and axle, pulley, inclined plane, wedge, and screw. These machines can be combined to form compound machines. (tl)McGraw-Hill Education, (tc)Paul Giamou/Photolibrary/Getty Images, (tr)Martina Berg/age fotostock, (bl)Steve Cole/Photodisc/Getty Images, (bc)Hanson Ng/age fotostock, (br)Martin Poole/Getty Images

Machines How are machines useful? Increase speed - example the wheel Change directions – example the wedge Increase force – example a car jack Mechanical Advantage is the ratio of the output force to the input force. It tells the effectiveness of a machine. The input force is the force that a person or device such as a motor applies to the machine. The output force is the force that the machine applies to another object Mechanical advantage tells the number of times a machine multiples the input force.

Efficiency Mechanical Advantage Input force (man) Output force (jack on the car) Efficiency You always put more work into a machine than you get out of it. This is a fundamental scientific law. Efficiency is the ratio of output work to input work, It is measured in percentages. Work output increases as efficiency of a machine increases.

HOMEWORK Complete the practice problems in your textbook pages 107, 110, and 112. Do #1-12 all. Show your work and write the equations each time.

Assessment 1. Using the scientific definition, which statement is always true of work? It is difficult. A It involves levers. B It involves a transfer of energy. C CORRECT It is done with a machine. D

Assessment 2. Which cannot be done by a machine? increase force increase work B CORRECT change direction of a force C increase velocity D

Assessment 3. Which factor increases as the efficiency of a machine increases? work input A work output B CORRECT friction C input force D

Assessment 4. What term indicates the number of times a machine multiplies the input force? efficiency A power B mechanical advantage C CORRECT resistance D