1. What is science?
2. How is it done these days?
3. The origins of modern science.
4. Laws of motion, gravity.
5. The nature of energy.

1. Definition of work
2. Definition of energy
3. Definition of power, kilowatts, horsepower
4. Forms of energy: kinetic and potential
5. Kinetic energy related to mass and speed
6. Many types of potential energy
7. What is heat?
8. Energy of mass, E=mc²

• Science proposes that the first event in our universe, its creation, was the "big bang". The very first thing that appeared during the “big bang” event was energy. The entire amount of energy that currently is contained within the universe appeared at once, in an infinitely small space. We think that it is a large amount, the entire energy of the universe, but when something is created from nothing then any amount is huge. We assume that since the big bang, in our universe, nothing else has been created from nothing.
• At first the energy was so concentrated that it's form was unlike anything we have ever seen. After some expansion of the universe the density of the energy decreased until atoms formed, maybe after 100,000 years.
• This illustrates two of the most important things about energy, that the total amount is fixed and that it can change its form.
• Today’s lecture is to get us up to speed about what constitutes energy and provide us with a series of definitions.
• Energy is the most important topic in today’s science. A huge amount of research effort is being put into this field .

• Work is done whenever a force is exerted over some distance.
• Pick up a book and raise it 1 foot. Then your muscles applied a force equal to the weight of the book over a 1-foot distance.
• If you were in a car accident and the fender was smashed in, then work has been done moving the metal of the fender the smashed distance.

• A small force moving an object a long way can produce the same amount of work as a large force over a small distance.

• Energy is defined as the ability to do work.
• If a system can exert a force over some sort of distance then the system possesses energy.
• The amount of a system’s energy is a measure of how much work the system could do.
• When a system runs out of energy then it can no longer do any work.

• Power provides a measure of the amount of work actually done (or energy expended) and the time it took to do the work.

P = W/t

• More power is needed to run up a flight of stairs than to walk up. Note that the work is equivalent, you moved your mass a distance, but the time was different.
• The watt is a unit of power, and 1000 watts is called a kilowatt. The rating of 100 watts on a light bulb is telling us the rate at which energy is being consumed when the light bulb is on.
• When you pay your energy bills, for instance electricity, you pay based upon how much energy you consume. This is obtained by multiplying the power of the equipment by the length of time that the equipment ran, ie power*time.
• Today's residential electric rate in Tucson is $0.10/kilowatt hr. This means that a 100 watt light bulb cost 1 cent an hour to operate.
• Horsepower is another unit of power.
• Interestingly, James Watt, after whom the watt was named, invented the term horsepower. He invented steam powered water pumps. He sold them in units of horsepower.  He found that a horse could raise 550 pounds of water up 1 foot in 1 sec of time, when using horses to power the waterpumps in mines. So a 350 horsepower car engine is capable of producing enough power to raise 350*550 = 192,500 lbs. = 96 tons of weight 1 foot in 1 sec.

• A force causes a mass to accelerate.
• F = ma
• W = Fd
• Energy is the ability to do work
• P = W/t
• E = Pt

• Perhaps the most important effort in fundamental science is trying to recognize the forms that energy can take. We recognize two very broad categories:

Kinetic
Potential

• Kinetic energy is the energy associated with moving objects. Since W=Fd, then kinetic energy is the energy associated with the actual moving of the mass over the distance d.
• Potential energy is the energy that is associated with the potential to move the mass over a distance. Ie., the mass could be moved this far if energy were released.
• Imagine a ball flying through the air. Something did work to get the ball, a mass, to be moved by the distance that it is travelling. Therefore, kinetic energy has been applied to the ball. This energy is related to the force that moves the mass of the ball over the distance that it travels. In turn, if the ball were to hit a window, then the mass of the window would be displaced, in fact, it may break, and we would say that kinetic energy was applied to the window.
• Anything that is moving has kinetic energy.
• Several things affect the kinetic energy.
1. Mass: The heavier the object the more kinetic energy. Eg. Throw a bowling ball through a window, it carries more energy than a golf ball thrown at the same speed.
2. Velocity: The faster something is moving then the greater the force it can exert. Eg a high-speed collision creates more damage to a car than a low speed collision.

• Speed is more important in determining energy than mass.
• An object that is raised above the earth has the potential to do work if it fell to the earth. The amount of work that it could do is equal to the amount of work that was used to raise the object in the first place. This unused, but available, ability to do work is called potential energy. In this case we would call it gravitational potential energy.
• Eg. Raise your book 1 foot above the table. If you let go of it, then it would have kinetic energy equal to the work required to lift it in the first place.
• The potential energy stored in gasoline is called chemical potential because the force that would release the energy is in the chemical bonds. Likewise for batteries, or even food. There are lots of examples of things with chemical potential.
• Think of potential energy as energy that could be turned into kinetic.

• Heat is a special form of energy that took a while for scientist to understand.
• Many years ago, ~200, it was believed that heat was a fluid. This is because if you put a cold item in contact with a hot one then the hot one would get cooler and the cool one would get hotter until they ended up at the same temperature. This is like attaching a full container of water to an empty one, the water would flow from the full one to the empty one till both had water up to the same height.
• Some objects heat faster than others. Eg diamond heats faster than any other material.
• Some expand upon application of heat, some do not.
• The fluid was called “caloric” and the volume of this fluid was measured in calories.
• A lump of coal was assumed to contain more caloric than a lump of ice.
• Joule did the demonstration or experiment that led to an understanding that heat was a form of energy. He had weights rotate a paddle wheel in water and observed that the transfer of kinetic energy heated the water.

• So, what is heat?
• Heat ends up being the energy contained in atoms as they vibrate back and forth within an object. If you touch an object whose atoms are moving fast back and forth, then the collisions will exert a force, you feel this force as hot.
• Click to see a movie of the atoms of quartz as a function of temperature.

• Waves hitting the seashore are kinetic, it is the energy of the atoms in the water being displaced and moving and then hitting the shoreline.
• Sound has energy involved because air is being displaced. Speakers work by oscillating the air back and forth.

• Einstein's E=mc² is the equation that tells you how much energy is in mass.
• We see some of this during radioactivity. An atom, such as uranium, spontaneously disintegrates into smaller pieces, lighter atoms. However, the sum of the mass of the lighter atoms is less than the mass of the original atom. The difference is given off as energy. The energy associated with mass is enormous. In examples like radioactivity and nuclear bombs, it is only a small amount of mass that has been converted to energy.
• Eg: 1 grape has enough energy to heat your home for 12,000 years.