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.

Chapter 12 Section 2 How Machines Do Work

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.

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.

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

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

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

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

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.

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