Energy Physics introduction

The Law of Conservation of Energy ( the First law of Thermodynamics )  Energy cannot be created or destroyed; it may be transformed from one form into another, but the total amount of energy never changes.

What is Conversion of Energy  Falling object converts gravitational potential energy into kinetic energy  Friction converts kinetic energy into vibrational (thermal) energy and makes things hot (rub your hands together)  Doing work on something changes that object’s energy by amount of work done, transferring energy from the agent doing the work

Energy is Conserved!  The total energy (in all forms) in a “closed” system remains constant Energy Conservation Demonstrated in the following example:  Roller coaster car lifted to initial height (energy in)  Converts gravitational potential energy to motion  Fastest at bottom of track  Re-converts kinetic energy back into potential as it climbs the next hill

What is Energy  Energy is “the ability to do work”  The combination of energy and matter make up the universe:  Matter is substance, and energy is the mover of substance.  Energy is nature’s way of keeping score. We sense energy only when the score changes, either a transformation from one form of energy to another, or a transfer of energy from one point to another.

How is energy divided? Potential Energy Kinetic Energy All Energy Gravitation Potential Energy Elastic Potential Energy Chemical Potential Energy

Potential vs. Kinetic Energy Potential Energy  energy of position or energy in storage.  Examples :  Water behind a dam  Hammer over head  Food on the plate Kinetic Energy  energy of motion, the form capable of doing work  Flowing water  A falling hammer  Electrons regenerating ATP in a biologic cell

Potential Energy  Calculated with equation :  PE = mgh  Where PE = Potential Energy  M = mass in kg  G = force of gravity  H = height (meters)  This represents a number value that we can give to the potential Energy that is stored and waiting to be used later

Types of Potential Energy 1. Gravitational Potential Energy (GPE) oPotential energy due to an object’s position oP.E. = mass x height x gravity 2. Elastic Potential Energy (EPE)  Potential energy due compression or expansion of an elastic object. 3. Chemical Potential Energy (EPE) oPotential energy stored within the chemical bonds of an object

Practice potential energy problems Problem #1 A man with a mass of 80 kg is standing on the edge of a table 1.5 m above the ground. What is the mans potential energy? Problem #2. A city is situated 4080 m above sea level. If a car with a mass of 905 kg is driven from a location that is 1860 m above sea level to the city, what is the increase in potential energy?

What is Kinetic Energy oEnergy an object has due to its motion oK.E. =.5(mass x speed 2 )

Kinetic Energy Practice Problems (KE = ½ mv 2 ) Problem one A 4 kg bowling ball rolls down the lane at 10 m/s. What is the kinetic energy at the moment before it hits the bowling pins? Problem two Afterschool at baseball practice Alex throws a.25 kg baseball at a respectable speed of 50 m/s. What is the kinetic energy as the ball leaves his hand?

Work and its close relationship to Energy Work  is equal to the force that is exerted times the distance over which it is exerted. W = F x d Where: W = Work (units in joules ) F = Force (remember F = Mass X Acceleration) D = Distance Work is done when a force is exerted over a distance.

Work and Kinetic Energy Because work and kinetic energy can be equated, they must have the same units: kinetic energy is measured in joules. Work = Kinetic Energy

Work and Friction  If friction is present, the work done depends not only on the starting and ending points, but also on the path taken.  Friction is called a non-conservative force.  It will leak out energy from the system as heat

Work Practice Problem You carry a 20 kg suitcase upstairs, a distance of 4m. How much work did you do?  W = F x d  F = ma  = (20 kg) (10m/s 2 ) = 200 N  W = F x d  = (200 N) (4m) = 800 J How much work will this man do if he carries the groceries 50 feet forward? As long as this person does not lift or lower the bag of groceries, he is doing no work on it. The force he exerts has no component in the direction of motion.

Power Power measures the rate (speed) of work done or the rate (speed) at which energy is expended.  Power is the amount of work done, divided by the time it takes to do it.  The units for Power are Watts (sound familiar?) Power (watts) = work (joules) / time (sec)  P = W/t

Power Since work performed equals energy spent the equation for power can also be written like this: Power (watts) = energy (joules) / time (sec) The watt is defined as the expenditure of 1 joule of energy in 1 second. (75 watt light bulb consumes 75 J/sec)

Practice problem on Power (Power = Work / Time Your CD system, uses 250 watts of electrical power. You play it for 3 hrs. How much energy is used? About how much would it cost? If one kWh is $.08. A mechanic uses a jack to lift a truck and does 7258J of work. If he lifts the truck.45s, what was the power output? Problem #1 Problem #2

How Energy Work and Power all go together: QuantityDefinitionUnits Forcemass x accel.newtons Workforce x distancejoules Powerwork / timewatts Energypower x timejoules

Energy Conversions Remember that energy is never created or destroyed, but can be changed from one form to another. So next we will take a look at the various forms of energy. Be careful….. For each form of energy there can only be two types (Potential or Kinetic Energy!) ex. You can have potential electrical energy or kinetic electrical energy potential nuclear energy or kinetic nuclear energy…….and so on

Forms of Energy 6 Main Forms of Energy 1.mechanical energy 2.electromagnetic energy 3.thermal (heat) energy 4.electrical energy 5.chemical energy 6.nuclear energy

What is the source of our energy here on Earth?  The source of practically all our energy is the Sun.

What is Mechanical Energy? o Energy due to a object’s motion (kinetic) or position (potential). The bowling ball has mechanical energy. When the ball strikes the pins, mechanical energy is transferred to the pins!

Examples of Mechanical Energy

What is Electromagnetic Energy?  Light energy  Also called radiant energy  Is the energy of electromagnetic waves  This radiation is made of waves that move at the speed of light.

Examples of Electromagnetic Energy Includes energy from gamma rays, xrays, ultraviolet rays, visible light, infrared rays, microwave and radio bands

What is Electrical Energy?  Energy caused by the movement of electrons  Easily transported through power lines and converted into other forms of energy

Examples of Electric Energy

What is Chemical Energy?  Chemical Energy is energy stored in the bonds of chemical compounds (atoms and molecules).  It is released in a chemical reaction  Usually, once chemical energy is released from a substance, that substance is transformed into an entirely new substance.

Examples of Chemical Energy

What is Thermal Energy?  Heat energy  The heat energy of an object determines how active its atoms are. A hot object is one whose atoms and molecules are excited and show rapid movement. A cooler object's molecules and atoms will show less movement.

Examples of Thermal Energy

What is Nuclear Energy?  Nuclear energy is the energy released by a nuclear reaction, Nuclear energynuclear reaction  by fission or fusion.  Nuclear energy uses fuel made from mined and processed uranium to make steam and generate electricity.uranium  Nuclear generation is the only source of electricity that can produce large amounts of power –reliably without emitting greenhouse gases.greenhouse gases

Energy Transformations and the Conservation of Energy  Work is done when energy is transferred from one object to another.  Accounting for all forms of energy, we find that the total energy neither increases nor decreases. Energy as a whole is conserved.

QUIZ TIME! What type of energy cooks food in a microwave oven? ELECTROMAGNETIC ENERGY What type of energy is the spinning plate inside of a microwave oven? MECHANICAL ENERGY

QUIZ TIME! Electrical energy is transported to your house through power lines. When you plug an electric fan to a power outlet, electrical energy is transform into what type of energy? MECHANICAL ENERGY

QUIZ TIME! What energy transformation occurs when an electric lamp is turned on? ELECTRICAL ENERGY  ELECTROMAGNETIC ENERGY

What types of energy are shown below? Mechanical and Thermal Energy (Don’t forget friction)

What type of energy is shown below? Chemical Energy

What types of energy are shown below? Electrical, Mechanical and Electromagnetic Energy

What type of energy is shown below? Chemical Energy (yummy)

What type of energy is shown below? Thermal Energy

What types of energy are shown below? Mechanical, Electromagnetic, Electrical, Chemical and Thermal Energy