Work, power, and machines CHAPTER 14 Work, power, and machines

SECTION 14.1

I. WORK AND POWER A. WHAT IS WORK? Work requires motion Work is a product of force and distance Work depends on direction

Work depends on direction

B. CALCULATING WORK Equation: Work = Force x Distance W= F x d Work is measured in Joules (SI unit) 1(Newton)(meters)= 1(Joule) Work - Joules (J) Force – Newton's (N) Distance – Meters (m) Power – Watts (W) Time – Seconds (s)

B. CALCULATING WORK Work = force x distance Work = 1600N x 2.0m Work = 3200(N)(m) = 3200J Imagine Isaac lifting Joseph into the air repeatedly. How much WORK does he do with each lift? He lifts Joseph 2.0m and exerts an average force of 190 N? W = ________ x________ = _________ W= 190N x 2.0 m W = 380 N x m = 380J

C. What is Power? 1.Power – a quantity that measures the rate at which work is done Power = Work /Time or P = W/T 2. Power is measured in Watts (W) 3. Watts is the amount of power that is required to do 1 Joule of work in 1 second

C. Calculating Power How much power is used if a force of 25 Newton's is used to push a box a distance of 10 meters in 5 seconds. How much power is used? P= work Work isn’t given so what time do you do? Find work first (W= F x d) W= 25N x 10m= 250 Work 250J = 50Watts time 5s

D. James Watt and Horsepower Besides a watt, another common unit of power is the horsepower (hp) 1 (hp) = 746 watts

Section 14.2 Work and Machines

A. Machines Do Work A machine is a device that changes a force. Machines make work easier They change the size of force needed, the direction of a force or the distance over which a force acts.

B. Work Input and Work Output The force you exert on a machine is called the input force. C. Work Output of a machine The force that is exerted by a machine is the output force.

Mechanical Advantage and Efficiency SECTION 14.3 Mechanical Advantage and Efficiency

A. Mechanical Advantage The number of times that the machine increases an input force.

1. Actual Mechanical Advantage AMA- equals the ratio of the output force to the input force 2. Ideal Mechanical Advantage (IMA) is mechanical advantage in the absence of friction

B. Calculating mechanical advantage MA = output /input

Simple Machines 1. Simple Machines – one of six basic types of machines of which all other machines are composed

The Lever Family Simple lever Wheel and Axle Pulley

Levers are divided into 3 different classes 1st class – have a fulcrum in the middle of an arm. Input force acts on one end and the other end applies an output force

Second Class Lever The fulcrum is at one end of the arm and the input force is applied at the other end

Third class lever Multiply distance rather than force. As a result, they have a mechanical advantage of less than 1. ( The human body has many)

Pulleys Pulleys are modified levers

The Inclined Plane Family Multiply and redirect force Ex. Apply force to push an object up a ramp, The ramp redirects force to lift the object upward

Inclined Planes 1. Wedge – turns downward force into forces directed out to the sides

Inclined Planes 2. Screw- an inclined plane wrapped around a cylinder

Inclined Planes 3. Inclined plane- changes both magnitude and the direction of force

Compound Machines Combines two or more simple machines

I. Energy and Work Energy measured in joules Transfer energy from doing work Ex. Slingshot