Objectives : Objectives Define energy & name the unit of measurement
Define mechanical energy
Calculate potential and kinetic energy
State the law of conservation of energy What is Energy? : What is Energy? Energy is the ability to do work
This is similar to our every day definition of energy. You can’t run up the stairs (work) without energy!
We have lots of types of energy. Can you name a few? Forms of Energy : Forms of Energy Mechanical Energy : Potential energy + Kinetic energy = Mechanical energy Mechanical Energy Potential energy is stored energy or energy of position
Kinetic energy is the energy of motion Kinetic Energy : KE = mv2 / 2
M = mass of the object (kg)
V = velocity of the object (m/s)
Measured in Joules Kinetic Energy Let’s Practice : Let’s Practice What is the kinetic energy of this car when it is traveling 38.0 m/s?
KE = m v2 / 2
= (1550 kg)(38.0 m/s)2 / 2
KE = 1,119,100 J Car’s mass = 1550 kg Potential Energy : PE = mgh
m = mass (kg)
g = gravitational acceleration due to gravity
h = height above earth's surface (m)
Measured in Joules Potential Energy Let’s Practice : Let’s Practice A rock has a mass of 840 kg. The center of mass is 29.0 m above the ground. How much energy does it have?
PE = mgh
m = 840 kg
g = 9.8 m/s2
h = 29.0 m
PE = (840 kg)(9.8 m/s2)(29 m)
= 238,728 J Energy Conversion : Energy Conversion Energy can be changed from one form to another. Changes in the form of energy are called energy conversions. Conservation of Energy : Conservation of Energy Energy can change from one form to another, but the total amount of energy is always the same.