I spent my Summers in southern Wisconsin until I was 16 years old. This summer home was by a swampy section of a lake and generally removed from near civilization. Typically house waste was separated into the burnable and nonburnable where the burnable was deposited into a 50 gallon drum and the other into a trash can which monthly was hauled to the local dump. For perspective this was in the late 1950's - 1960s. If the trash was wet from rain I was instructed to pour some kerosene in the drum then toss a kitchen match in. That got it burning. Of course it stunk but such was life back then. It had rained in the evening and my Dad told me to burn the trash. The kerosene can was empty so I poured in a robust amount of gasoline that was for the lawnmower. I had done this previously and if I quickly tossed in a wooden kitchen match it went "poof" and proceeded to burn the trash, however, I didn't have any matches of any kind. I headed off with the hot sun on my back and my trusty sling shot in my pocket. As usual I disappeared for a couple hours. Upon returning to the homestead my Dad caught me and inquired why the trash wasn't burned. I simply said I didn't have any matches. Well there was the typical range of derogatory remarks and he concluded with "I'll do it my self!!". Having been the local engine and radio repair kid I had a notion that tossing a match in the drum wasn't a good idea. My Dad wasn't inclined to listen to me, but he did get cautious. He tossed a wooden kitchen match in the drum and "FAZOOM" burning garbage sailing 20 feet in the air and Dad charging away. Me? Well I was laughing hysterically which got me grounded for a few days.
During this time off I knew why the vaporized gas burned and it was surely a powerful explosion. What was power? The gas had energy. I was in a catholic elementary school then and drove the nuns nuts reading Physics texts from the "ADULT" section of the city library. Upon some reading it all made complete sense. I'll leave out units at this point and use a general narrative.
Energy allows work to happen. Some things have the potential to do work: potential energy. Other things are moving and do work: kinetic energy. Energy isn't all this simple but this is sufficient for this discussion. What about power? So beautiful, a metric on energy use! Power is the rate we use Energy or put this way Power = Energy/time. Consider the drum episode. There was the same amount of gas in the morning drum as in the afternoon (perhaps a bit less in the afternoon from gas vaporization. we will ignore this) so there was the same Energy morning and afternoon. The hot sun vaporized the gas, it then mixed with air oxygen in the afternoon and burned very, very fast. Ah, time was very short so Power got very big from the same Energy because the Energy was used fast.
My mind exploded with examples such as internal combustion engines, firecrackers, kerosene lamps and many electrical devices, one of which is discussed in the side column.
We need to put some units to these terms so they can be measured. Using SI units Power is measured in watts, Time is measured in seconds and Energy in joules. You can say that a watt second is one joule. Actually one joule is better defined as a force of one newton applied over a distance of one meter but a watt second is good for this discussion. You do use energy terms regularly. Take a look at your electric bill from your local utility and notice you are billed for kilowatt hours which is Energy and one kilowatt hour = 3,600,000 joules. Your electric bill in joules would be a huge number of energy use so we use and feel comfortable with kilowatt hours. Yes folks you do buy and pay for energy and the rate you use the energy is power.
Are you considering purchasing an electric vehicle? Its useful to discuss potential energy in batteries. Obviously batteries supply electricity. Since we know how to convert electrical energy to move a car it is pretty clear that we can measure the rate we use this energy in watts. So if there are batteries with a lot of stored energy we can use to run a car or truck until the stored energy in the battery is used up. Then it is necessary to replenish it by a charging mechanism. No surprises here because we recharge many types of batteries.
Automotive manufactures provide a distance their vehicles will travel on one full charge before the battery needs to be recharged so it can supply energy again. Today the range is around 200-350 miles. So the battery provides energy that we use to make power and move the car. There is some basic physics going on here but I'll bypass that. For the present we will use experience and common sense.
What can cause the EV to use energy faster or
to make more power? Going up a hill, rapid accelerating adding weight or towing weight basically the same things that would burn more gas with a gasoline powered car. According to Motor Trend a fully charged heavy duty pickup truck battery pack has less onboard energy than 4 gallons of gasoline. Interesting comparison.
Pickup trucks need to make a lot of power and they use a lot of battery energy doing this.
Pickups often are used to haul heavy materials as well as tow boats, campers or a heavy trailer with a front end loader. With this kind of load that 250 mile range is now reduced to 100 miles (Motor Trend). Wow, that might be a big problem.
This is why understanding the relationship between energy and power is vital for living in an entangled world. We need to make wise and accurate decisions.
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