Transcript Ch. 10 Energy, Work, and Simple Machines

Ch. 10
Energy, Work, and Simple
Machines
Milbank High School
Sec. 10.1
 Objectives




Describe the relationship between work and
energy
Display an ability to calculate work done by a
force
Identify the force that does work
Differentiate between work and power and
correctly calculate power used
Energy
 The ability to produce change in itself or the
environment
 Mechanical Energy

Ability to do work
 Potential Energy

Stored energy
 Kinetic Energy

Energy of motion
Kinetic Energy
•Utilizes motion equations and
Newton’s second law of motion
•Produces
Work
 Transfer of energy by means of forces
 1/2mv1 – 1/2mv0 = Fd
so…
so…
 W = Fd
or…
 K1 – K0 = W or ∆K = W
 Measure in Joules (kg·m2/s2)
 K = 1/2mv2
Problems
 Example Problem Pg. 226

Calculating Work
Practice Problems Pg. 227
Calculating work at an angle
 W = Fd cos Ө
 Example Problem Pg. 228

Force and Displacement at an Angle
Power
 Power is the rate of doing work, or the rate at
which energy is transferred
 P = W/t
 Power is measure in watts (1 joule of energy
transferred in one second)
Sec. 10.2
 Obejctives
 Demonstrate knowledge of why simple
machines are useful
 Communicate an understanding of mechanical
advantage in ideal and real machines
 Analyze compound machines and describe
them in terms of simple machines
 Calculate efficiencies for simple and
compound machines
Machines
 Ease the load by changing either the
magnitude or the direction of a force as
it trasmits energy to the task
 Basically….make tasks easier
 Wi
 work input, the work you do
 Wo
 Work output, the work the machine
does
Mechanical Advantage
 The ratio of resistance force to effort force
 Fr/Fe
 Hopefully its greater than 1
 Effort force

The force you exert on a machine
 Resistance force

Force exerted by the machine
Ideal Mechanical Advantage
 Ideal Machine: all energy transferred, or in
other words W0 = Wi
Ideal Mechanical Advantage = de/dr
Measure distances….with MA, you measure the
forces
Efficiency
 An ideal machine has equal output and input
 Dpes it really ever happen?
 Efficiency can be defined as W0/Wi x 100 (for
a percent)
 Or…MA/IMA x 100

Efficient machines have an MA close to the
IMA
Simple Machines
 Lever
 Pulley
 Wheel and Axle
 Inclined Plane
 Wedge
 Screw
Compound Machines
 Consists of two or more simple machines
 The resistance force of one becomes the
effort force of the other
 Example Problem Pg. 237
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Bicycle Wheel