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When gas, oxygen, and heat are combusted in a car engine, how is it possible that it creates enough energy to move a car that weighs over 3000 pounds?
Question Date: 2010-05-17
Answer 1:

Gas has a lot of energy stored in its chemical bonds. When gas reacts with oxygen that energy is released and hot carbon dioxide gas is formed. The hot gas is used to drive pistons in the car's engine and make it move. Essentially the chemical energy is converted to heat and mechanical energy. Moving a 3000 pound car requires energy to accelerate the car and then once it is up to speed, it requires energy to keep moving because of friction and air resistance. Neglecting friction and air resistance, we can calculate how much energy it takesto move a car a reasonable distance using the following equations.

Force = Mass * Acceleration
Work = Force * Distance

1 gallon of gas contains about 130 megajoules (or 130,000,000 joules) of energy.

For the car:
Mass = 3000 pounds ~ 1400 kg

A reasonable acceleration might be from 0 to 60 miles per hour in 20seconds which corresponds to a constant acceleration of about 1.3m/s2.

Distance = 1/2*acceleration*(time)2
So at this acceleration for 20 seconds, the car will travel 260 meters or 0.16 miles.

1400 kg * 1.3 m/s2 = 1820 Newtons

1820 Newtons * 260 meters = 470,000 joules

470,000 Joules is less than 5% of the energy stored in 1 gallon of gas. However we must also consider that car engines are generally only20% efficient and that friction and air resistance also increase the energy requirement for moving a car. Even when these factors are accounted for, gas still stores ample energy to move a 3000 pound car.

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