# Watts in Coffee, Pot and Brakes?

click to enlarge
• Diagram illustrating conservation of motion by Don Garlick.

I am reading a full page ad in our local newspaper: "... miracle idea ... heating bills hit rock bottom ... miracle heater is a work of engineering genius ... so advanced, you simply plug it into any wall outlet. It uses less energy than it takes to run a coffee maker. Yet it produces an amazing 5,119 BTUs (note: 5,119 BTUs per hour = 1,500 watts*) ... get the imported miracle heater alone for just \$249."

This ad reveals a need for energy education. Converting electricity into heat is no miracle — it's too easy. All energy tends to degrade into heat. The reverse, converting heat into electricity, is not easy; a typical power station runs at only 30 percent efficiency. That's why my roof has solar hot-water collectors.

POT: Burning fossil fuels (fossilized sunlight) to produce electricity at 30 percent efficiency, then using that in a metal halide lamp at 24 percent efficiency to grow pot indoors, is highly inefficient! Perhaps we should legalize pot, thereby allowing the use of nature's "grow light" with no carbon emissions.

COFFEE: My 1,000 watt coffee maker boils a liter of water in 6 minutes = 100 watt-hours (as expected from water's heat capacity).

DRIVING: A 2,000 kg SUV at 100 kilometers per hour (62 mph) = 214 watt-hours of kinetic energy (1/2 mv^2). At half that speed it has one-quarter the energy and braking distance. Braking converts kinetic energy into heat — unless you drive a hybrid which decelerates by charging a battery. We should all drive lighter vehicles, and drive defensively: In a head-on collision between two cars of mass m and 2m, momentum (the product of mass and velocity) is conserved: 2mV - mV = mV. After the collision, assuming both stick together with new velocity v, 3mv = mV so that v = V/3. The heavier car changed its velocity by 67 percent, the lighter by 133 percent. Total kinetic energy decreased to 1/9 its pre-collision value, much having been converted into stressed steel and heat.

Conclusions: Drive slowly, thank Caltrans for center dividers, don't grow pot indoors and beware of "miracles."

#### Don Garlick

Bio:
Don Garlick is a geology professor retired from Humboldt State University. He invites any questions relating to North Coast science, and if he cannot answer it he will find an expert who can. E-mail dorsgarlick@yahoo.com.

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