Bell Ringer 3-2-10

1. Bell Ringer 3-2-10 • What is the formula for work? • What are the units for work? • If I pull a rope towards me but it doesn’t move, is that considered work? • Work includes force and motion in the _______ direction.

2. Chapter 12 Section 2How Machines Do Work

3. Machines are devices that make it easier to do work. • Machines change the way a person does work, not the amount of work that needs to be done.

4. How do Machines make work Easier? • By changing the amount of force you exert • By changing the distance over which you exert the force • By changing the direction in which you exert the force.

5. Input force is the force you exert on a machine. • The input force moves the machine a certain distance, called the input distance. • Input Force x Input Distance = Input Work

6. Output force is the force a machine puts on an object. • The output distance is the distance over which the machine exerts the force. • Output force x Output Distance = Output Work

7. Mechanical advantage is the number of times a machine increases a force exerted on it. • Mechanical advantage = Output force Input force

8. Some machines make work easier by allowing you to exert a smaller force over a longer distance. • Other machines allow you to exert your force over a shorter distance. • Other machines allow you to change the direction of input force

9. Efficiency is the ability to convert input work to output work, calculated as: • Efficiency = output work x 100% input work . • Oil, or another lubricant, can increase efficiency.

10. Friction reduces efficiency by converting some work into heat. • The efficiency of a real machine is always less than 100 percent because of friction.