Energy ENERGY
Energy Defined Energy is the ability of an object to produce a change in itself or the environment.
Energy Transfer Work is done when energy is transferred from one form of energy to another.
The Units for Measuring Energy Are the same as the units for measuring WORK JOULEs in the SI system FOOT-POUNDS in the British System
TYPES OF ENERGY
Mechanical Energy Energy is the ability to do work
Mechanical Energy(ME) - enables an object to do work A. Kinetic Energy (E k ) - energy of motion B. Potential Energy(E p ) - stored energy
Gravitational Potential Energy An object lifted against the force of gravity has stored energy. UNIT= JOULE
Gravitational Potential Energy Only changes in potential energy can be measured E p = mgh m= massg= gravityh= height
As an object, such as a boulder, begins to move, it gains velocity. Gaining velocity increases the object’s kinetic energy.
Example Problem Legend has it that Isaac Newton “discovered” gravity when an apple fell from a tree and hit him in the head. If a 0.20 kg apple fell 7.0 m before hitting Newton, what was its change in E p during the fall?
Kinetic Energy Unit: Joules
Kinetic Energy Examples Pitched baseball 150 J (148 m/s) Football linebacker 4500 J ( m/s)
Example Problem A greyhound at a race track can run at a speed of 16.0 m/s. What is the KE of the 20.0 kg greyhound as it crosses the finish line?
Work Work is the transfer of energy from one object to another, or... The change in KINETIC ENERGY!
E k and E p are constantly changing.
Law of Conservation of Energy Energy cannot be created or destroyed. ENERGY is merely transformed.
APPARENT LOSS OF ENERGY FRICTION WASTES ENERGY BY CHANGING USEFUL ENERGY INTO HEAT
Total Energy At any point, the total energy of an object E t = E k + E p + HEAT
Potential Energy to Kinetic Energy
Law of Conservation of Energy
ELASTIC POTENTIAL ENERGY
Elastic Potential Energy Sling shots Trampolines Rubber bands Rubber balls
A Jack in the box has stored energy in a compressed spring.
k = force to stretch divided by distance stretched The Elastic Constant
ELASTIC POTENTIAL ENERGY E EP = 1/2 kd 2
Elastic Potential Energy If a spring of stiffness constant (k) is stretched an amount (d), the elastic potential energy stored in the spring is equal to 1/2 the the spring constant times the square of the distance stretched.
An automobile stores chemical energy in the gasoline.
Thermal Energy The total energy of vibrating atoms and molecules that make up a substance. Temperature is the average KINETIC ENERGY of a substance.