2.How Is Sound Actually a Form of Energy? in What Medium Do Sound Waves Travel?

1.What is the difference between energy and power? What is a unit of power? How does speed relate to power?

Power is energy per unit time. It is a rate of change, and describes a flow of energy. The SI unit for power is Watts, which are Joules per second, Joules being the SI unit of energy. Another common unit for power is horsepower, with 1 horsepower = 736 Watts.

The kinetic energy of an object or particle of mass m is T = mv2/2. Power is the rate of change of energy, or work per unit time. So to calculate power, you can compute the change in energy (proportional to the square of the speed) divided by the time period.

2.How is sound actually a form of energy? In what medium do sound waves travel?

Sound waves are longitudinal waves, which carry and transmit energy by alternately converting it from potential to kinetic energy as the medium gets compressed and then rarified in an oscillatory fashion. The amplitude of the wave is the degree of compression that comes with each passing wavefront. The energy in the wave is proportional to the square of this amplitude.

3.Give an example of change of energy from potential to kinetic; from kinetic to potential.

A pendulum swinging back and forth is a good example of transition between kinetic and potential energy. At the top of each swing, the pendulum is momentarily motionless, and thus has no kinetic energy. But at this point it has its maximum gravitational potential energy, being higher than any other point in its swing. As it swings past the vertical position (hanging straight down), its speed is at the maximum value, so its kinetic energy is at its greatest. At this point, the potential energy is at a minimum (we can define the scale so that this is zero potential energy).

4.What is a trophic level? Give some examples. How much energy is lost at each trophic level?

A trophic level is a link in the food chain. Tropic levels run from producers like plants and algae to apex predators like crocodiles and lions. As a general rule of thumb, in eating an organism from the next level down, the eater acquires only about 10% of the energy available in their meal. This is even worse at the bottom level, where plants generally only retain about 1% of the solar energy they receive.

5.If you eat 600 calories per day (roughly one dessert) below your energy needs, how long would it take to lose 10 pounds? How long would you have to walk (assuming 80 calories burned per mile walked) to lose 10 pounds?

One pound of body weight is approximately equivalent to 3,500 calories. To loose 10 pounds, you’d need to loose 35,000 calories worth of mass. Dieting at a deficit of 600 calories a day, this would take just over 58 days, or approximately two months. Alternatively, at 80 calories per mile, you’d have to walk 437.5 miles.

6.What makes a good conductor of heat? What makes a good insulator?

Metals are generally good thermal conductors, as the same valence electrons that make them electrically conductive also serve to conduct heat across the metal. There are also many non-metals that are good thermal conductors, perhaps most notably diamond. In these thermal conductors, microscopic vibrations called phonons transfer heat.

Good electrical insulators are usually also good thermal insulators. Air is a very good insulator, so materials like foam that are mostly air are often used in construction. The ultimate thermal insulator is of course vacant space.

7.Why does heat only flows spontaneously from a hot to cold object.

This is the second law of thermodynamics. The second law states that entropy, or disorder, will naturally increase and the system will become less ordered, unless we invest energy. Fundamentally, this is the result of combinatorics – the fact that there are many more available ways to arrange things in a disordered way than there are to order them. It is this same principle that makes a roll of 7 more likely than 2 or 12 when rolling two dice.

8.In what way is aging an example of the second law of thermodynamics?

The second law of thermodynamics defines time’s arrow, since systems always (unless we use energy to reverse the process) decay from order into disorder. Thus aging is the natural decay of any system.

9.If traveling to Europe, and the weather forecast says it is going to be 38oC. Should you wear shorts of a down jacket?

38 degrees Celsius is extremely hot, equivalent to 100.4 degrees Fahrenheit, so you should definitely wear shorts, and leave your down jacket home!