Unit 3: Work, Energy, and Power

Conservation of Energy!!

Energy as a tool in physics Energy is a very abstract notion, but it is a very useful and quantifiable notion We use the law of conservation of energy to predict behavior We rely on the fact that energy is not created out of nowhere Where did the energy we see around us come from? most of what we use derives from the sun some derives from other, exploded stars (nuclear fission) ultimately, all of it was donated in the Big Bang!

Energy cannot be created or destroyed It's the LAW! Of conservation of energy Energy cannot be created or destroyed

All energy can be broken down into 2 categories Types of Energy All energy can be broken down into 2 categories Energy! Kinetic Energy Potential Energy

K=½ mv2 Kinetic energy Energy! An objects kinetic energy is equal to…… Which has a bigger affect???? kinetic energy = energy due to motion

If this car had a velocity of 24 m/s and a mass of 1000 kg what was its kinetic energy when it entered your living room? 288000 joules 15000 joules 49000 joules 391000 joules

Ug = mgh gravitational Potential Energy Energy! An objects Gravitational Potential energy is equal to…… Energy! Ug = mgh Which has a bigger affect???? Potential energy = stored energy in earth 1644 m staircase

Calculate Spidey’s gravitational potential energy if he is 150 m up a building and his mass is 89 kg!!! 288000 joules 4388 joules 130830 joules 94224 joules

An objects Thermal energy is equal to…… Dissipated Energy An objects Thermal energy is equal to…… This is energy that is hard to reclaim from the system. Even though the energy is not lost, it is hard to convert into another form of energy. Energy! An object gives off thermal energy in the form of heat! This is where %75 of your energy goes!! kinetic energy = energy due to motion of molecules, but it is extreme hard to reclaim

Elastic and spring Potential Energy Energy! An objects elastic potential is equal to…… Relax! Right now you need to understand that it is another form of potential energy! Energy! Think bow and arrow, rubber bands, springs, catapults, sling shots, etc. Potential energy = stored energy in the spring

Mechanical vs. Non-mechanical energy Mechanical energy – Potential and Kinetic Energy The total mechanical energy of a system will be the sum of the potential and kinetic energy Energy! Non-Mechanical energy – everything else! Light, Sound, Chemical, thermal.

It's the LAW! Remember! Energy cannot be created or destroyed!! Of conservation of energy Energy cannot be created or destroyed!! So what happens to an object’s potential and kinetic energy as it moves?!? The point is: Energy is never lost… just transferred! So does an object lose or gain energy as it moves?!?

Doing “Work” on objects Work in physics is when energy is transferred into, out of, with in the system. Work in the system can result in a change in Kinetic Energy OR a change in Potential Energy. Can be positive (net gain in energy) or negative (net loss in energy) Work is accomplished by applying a FORCE through a DISTANCE. Work = Force x distance W = Fd Anytime there is a change in energy, you do work!

Lets say this fat kid pulls his wagon with a force of 300 N Lets say this fat kid pulls his wagon with a force of 300 N. How much work does he do on wagon if he pulls it for a distance of 35 meters? 8.57 joules 7,777 joules 4,322 joules 10,500 joules W = Fd

Units Work & Energy are scalar quantities. Joule (J) – SI unit for Work & Energy James Prescott Joule (1818-1889) – English physicist; studied heat and work. This led to the theory of conservation of energy. Developed Kelvin scale with Lord Kelvin.