The first law of thermodynamics, also known as Law of Conservation of Energy, states that energy can neither be created nor destroyed; energy can only be transferred or changed from one form to another (example: from light energy to chemical energy in food in photosynthesis)

The second law of thermodynamics says that the entropy of any isolated system always increases. Entropy is a gradual decline to disorder. A simple way to think of the second law of thermodynamics is that a room, if not cleaned and tidied, will invariably become more messy and disorderly with time. Heat is a less ordered form of energy – this is why in most energy transformations, some energy is “lost” as heat.

Example: A 100 Watt bulb uses 100 J/sec of electrical energy. If it is 20% efficient, then the bulb converts 20% of the electrical energy into light and 80% is wasted by being transformed into heat (ever felt a hot light bulb?).

Explain how the First Law of Thermodynamics (conservation of energy) occurs in this example.

Explain how the Second Law of Thermodynamics (law of entropy) occurs in this example.

Energy Conversions

Energy: The basic unit of energy is a Joule (J). Other units are calorie, kilojoule, British Thermal Unit (BTU), and therm.
1000J = 1 kJ
1000 cal = 1kcal
1 cal = 4.184 J
1 BTU = 1.05 kJ
1 therm = 100,000 BTU

Suppose a TV uses 200 J of energy. How many BTUs is this?

Sandy went to the gym and burned 500 kcal of energy. How many joules is this?

Killowatt-hours: kWh is kilowatt-hour. This refers to the amount of energy in kW consumed in one hour. This is actually a unit of energy, not time.

1 kWh = 1 kW x 1 hr = 3.6 x 106 J

Example: What is the energy consumed when using 2kW for 3 hours?

2 kW x 3 hours = 6 kWh

What is the energy consumed when using 5W for 2 hours?

Suppose a hair dryer uses 20 kJ of energy. How many kWh is this?

Follow these directions and answer the questions. 1. shine a pencil-thin beam of light on a mirror perpendicular to its surface. (if you don't have a laser light as suggested in the video, you can make a narrow beam from a flashlight by making a cone from black construction paper and taping it over the face of the flashlight.) how does the light reflect? how does the relationship of incident to reflected ray relate to the reflection of water waves moving perpendicular to a barrier? 2. shine a pencil-thin beam of light on a mirror standing on a sheet of paper on the table (or floor) so that you can mark the incident ray and reflected ray. (you can support the mirror from the back by taping it to a wooden block.) 3. mark a line on the paper representing the reflective surface. (the reflective surface of a mirror is usually the back edge.) 4. draw a dashed line perpendicular to the mirror surface at a point where the incident and reflected ray meet. this perpendicular is called a normal to the surface. 5. measure the angles between the rays and the normal. the angle of incidence is the angle formed by the incident ray and the normal to the surface. the angle formed by the reflected ray and normal is called the angle of reflection (r). what is the angle of incidence? what is the angle of reflection? 6. repeat for several different angles. (see report sheet for details.) what appears to be the relationship between the angle of incidence and angle of reflection? in science 1204, what was the relationship for these two angles made by the reflection of waves in a ripple tank? 7. roll a ball bearing so that it hits a fixed, hard surface (a metal plate) at several angles (including head-on). observe the way in which the ball bearing reflects. what generalization can you make about how a ball bearing reflects from a wall? have you proved that light can only behave like a wave?

Which example has gravitational potential energy? a. a horse slowing down from a run b. an apple about to fall from a tree branch c. a bicycle being pedaled down a horizontal path d. beaker sitting on the floor

An object with a mass of 1.5 kg changes its velocity from + 15 m/s to +22 m/s during a time interval of 3.5 seconds. what impulse was delivered to the objects?