unit 3: energy and momentum: part 1 energy
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Unit 3: Energy and Momentum: part 1 Energy. 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 - PowerPoint PPT PresentationTRANSCRIPT
Energy as a tool in Energy as a tool in physicsphysics
• Energy is a very abstract notion, but Energy is a very abstract notion, but it is a very useful and it is a very useful and quantifiablequantifiable notionnotion
• We use the law of We use the law of conservation of conservation of energyenergy to predict behavior to predict behavior– We rely on the fact that energy is not created out of We rely on the fact that energy is not created out of
nowherenowhere
• Where did the energy we see around Where did the energy we see around us us come fromcome from??– most of what we use derives from the sunmost of what we use derives from the sun– some derives from other, exploded stars (nuclear some derives from other, exploded stars (nuclear
fission)fission)– ultimately, all of it was donated in the Big Bang!ultimately, all of it was donated in the Big Bang!
Of conservation of energy
Energy cannot be created or destroyed
Types of EnergyTypes of EnergyAll energy can be broken down into 2
categories
Kinetic EnergyKinetic EnergyPotential EnergyPotential Energy
Kinetic energy
An objects kinetic energy is equal to……
K=½ mv2
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?
1) 288000 joules
2) 15000 joules
3) 49000 joules
4) 391000 joules
Potential Energy
An objects Gravitational Potential energy is equal to……
Ug = mgh
Which has a bigger affect????
1644 m staircase
Potential energy = stored energy in earth
Calculate Spidey’s Calculate Spidey’s gravitational potential gravitational potential energy if he is 150 m energy if he is 150 m up a building and his up a building and his
mass is 89 kg!!!mass is 89 kg!!!
1) 288000 joules
2) 4388 joules
3) 130830 joules
4) 94224 joules
Dissipated EnergyAn 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.
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
An objects elastic potential is equal to……
Relax! Right now you need to understand that it is another form of potential 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
Non-Mechanical energy – everything else! Light, Sound, Chemical, thermal.
Of conservation of energy
Energy cannot be created or destroyed!!
So what happens to an object’s potential and
kinetic energy as it moves?!?
So does an object lose or gain energy as it
moves?!?
The point is:Energy is never lost… just
transferred!
Doing “Doing “WorkWork” on objects” 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. How much work does he do on wagon if he pulls it for a distance of 35 meters?
A. 8.57 joules
B. 7,777 joules
C. 4,322 joules
D. 10,500 joules
W = Fd
UnitsWork & Energy are scalar quantities.
Joule (J) – SI unit for Work & EnergyJames 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.