Mechanical Energy
Energy and Power Energy could be in the form of
heat or work Heat is thermal energy Work is mechanical energy
Power is the rate at which work is performed
t
WP
Units SI vs. US System of units
(m, kg, s) vs. (ft, lb, s) Force (N)
Energy (1 N.m = 1 J) 1 kJ = 1,000 J; 1 MJ=1,000,000 J Also expressed as barrel of oil, Quad, eV
Power (1 J/s= 1 W) 1 kW = 1,000 W; 1 MW=106 W; 1 GW=109 W Also expressed as horsepower, BTU/hr
Units Convention Dr. Newton, Mr. Joule 235 newtons, 500
kilojoules, 10 kilograms 235 N, 500 kJ, 10 kg
1 mg= 0.001 g 1 kg=1000 g 1 Mg=1 metric ton
Power of ten notations
Prefix Symbol
10-12 pico p
10-9 nano n
10-6 micro
10-3 mili m
103 kilo k
106 Mega (million)
M
109 Giga (billion) G
1012 Tera (trillion) T
1015 Peta P
1018 Exa E
Types of Mechanical Energy Hydroelectric Tides Waves Wind
The Golden Rule of Mechanics
Whatever you lose in power you gain in displacement.
Output work can never be as much as input work
The main purpose of machines is to reduce the force (effort) required to do a particular job
Simple Machines
1. Ramp 2. Wedge 3. Screw
4. Lever 5. Wheel 6. Pulley
First Class LeversFulcrum is between the force and weight.
• Pliers
• Seesaw
• Scissors
Second Class LeversWeight is between the fulcrum and the force.
• Nutcracker
•Wheelbarrow
Third Class LeversForce is between the fulcrum and weight.
• Baseball bat
• Shovel
• Tongs
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