Work and Energy

Doing Work What is work? Using a force to transfer energy to an object causing the object to move in the direction of the force.

Doing Work Work = force x distance W=fd

So work is force times distance W = f·d or Joules = Newtons · meters Same work, different force 100 feet 200 feet 200 feet x 1000N = 200,000 J 100 feet x 2000N = 200,000 J

What is energy? Energy is the ability to do work Potential energy The energy stored in objects because of their position Kinetic energy The energy in objects that are in motion

What is energy? Energy is the ability to do work Kinetic energy KE = m·v² 2 20kg · (20 m/s) ² 2 20kg · 400m ² /s ² kg · m ² /s ² kg · m ² /s ² = 4,000 J

Kinetic energy KE = m·v² 2 5kg · (10 m/s) ² 2 5kg · 100m ² /s ² 2 500kg · m ² /s ² 2 250kg · m ² /s ² = 250 J 10kg · (10 m/s) ² 2 10kg · 100m ² /s ² kg · m ² /s ² 2 500kg · m ² /s ² = 500 J

Kinetic energy KE = m·v² 2 5kg · (10 m/s) ² 2 5kg · 100m ² /s ² 2 500kg · m ² /s ² 2 250kg · m ² /s ² = 250 J 5kg · (20 m/s) ² 2 5kg · 400m ² /s ² kg · m ² /s ² kg · m ² /s ² = 1,000 J

Kinetic energy A snail with a mass of 5g, traveling at.014 m/s has J of kinetic energy An 18-wheel truck traveling at m/s (43 mph) has 2,200,000 J of kinetic energy

Potential energy The energy stored in objects because of their position Gravitational Potential Energy Using force to do work against gravity The energy is stored until gravity can do work on it and pull it down to the ground

What is energy? Gravitational Potential Energy GPE = weight · height (why weight and not mass??) 150g · 2m = 300 J 300g · 2m = 600 J 150g · 4m = 600 J

Transferring Energy between Potential and Kinetic

100% Potential 0% Kinetic

50% Potential 50% Kinetic

0% Potential 100% Kinetic

50% Potential 50% Kinetic

100% Potential 0% Kinetic ?

50% Potential 50% Kinetic

0% Potential 100% Kinetic

50% Potential 50% Kinetic

100% Potential 0% Kinetic

50% Potential 50% Kinetic

0% Potential 100% Kinetic

50% Potential 50% Kinetic

100% Potential 0% Kinetic

50% Potential 50% Kinetic

0% Potential 100% Kinetic

100% Potential 0% Kinetic

50% Potential 50% Kinetic

0% Potential 100% Kinetic

50% Potential 50% Kinetic

100% Potential 0% Kinetic

0% Potential 100% Kinetic

100% Potential 0% Kinetic

0% Potential 100% Kinetic

100% Potential 0% Kinetic

0% Potential 0% Kinetic

Forms of Energy Mechanical Energy Since potential and kinetic energy can easily switch between them we measure the combined energy and classify it as mechanical energy.

Forms of Energy Thermal The kinetic energy due to the random motion of the particles that make up an object Which would have more thermal energy; an ice cube, a lake, or a boiling pot of water? The lake because it has so many more particles than the other two therefore more thermal energy.

Forms of Energy Chemical The energy of a compound that changes as its atoms are rearranged Chemical energy is a form of potential energy The total energy depends on the arrangement of the atoms in a compound Which has more chemical energy; water or sugar? Sugar has more chemical energy because of its large molecules (C 6 H 12 O 6 )

Forms of Energy Electrical Energy The energy of moving electrons Electrical energy is produced when magnets are moved through coils of wire

Forms of Energy Sound Energy The transmition of vibrating energy through the air A vibrating object causes the particles around it to vibrate. This kinetic energy is transmitted to our ears and we hear sound

Forms of Energy Light Energy The energy produced by the vibrations of electrically charged particles e−e−

Forms of Energy Light Energy The energy produced by the vibrations of electrically charged particles e−e−

Forms of Energy Light Energy The energy produced by the vibrations of electrically charged particles e−e− Photon of light

Forms of Energy Nuclear Energy The energy that comes from changes in the nucleus of an atom Atoms store a tremendous amount of potential energy because of the position of the particles in the nucleus When the nucleus of an atom is “split” we have nuclear fission This is the same energy given off by an atomic bomb

Forms of Energy Nuclear Energy The energy that comes from changes in the nucleus of an atom Atoms store a tremendous amount of potential energy because of the position of the particles in the nucleus When two or more atoms are force together to make a new atom it is called fusion Fusion how the sun produces its energy