# – Why do people say that driving a car at the same speed consumes less fuel in comparison to driving it at varying speeds over long distances

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– Why do people say that driving a car at the same speed consumes less fuel in comparison to driving it at varying speeds over long distances

In: Physics

Because actual driving consumes much less fuel than acceleration: you only need to overcome air resistance and not accelerate the car. If you drive at varying speeds, you need to accelerate often.

>Why do people say that driving a car at the same speed consumes less fuel in comparison to driving it at varying speeds over long distances

If you vary your speed it means that at some point you’re braking, either with your actual brake or via engine braking. That means you’re *deliberately* converting some of that precious fuel you used to accelerate into thermal energy to decelerate you.
All that is energy that is not used to propel you and therefore unnecessary waste if you accelerate again after the braking maneuver.

Newton’s first law of motion states that “An object at rest stays at rest and an object in motion **stays in motion with the same speed and in the same direction** unless acted upon by an unbalanced force.”

Objects tend to “keep on doing what they’re doing.” Because your car is moving at speed, it takes less energy to keep it moving at that speed.

They say because it’s usually true. And it’s true because breaking does not recover the energy that was used to accelerate the car, plus friction in air rises with velocity.

A car moving at constant speed doesn’t require any additional energy to keep moving. It only takes energy to stop, speed up, or change direction. Likewise, if a car is stopped, it doesn’t require energy to just sit there. It only takes energy to make it move. The most energy consuming part of your drive is making the car go faster, especially from a stopped position.

In other words, it takes a lot more energy to go from 0-60 than to just keep going 60. If you brake and accelerate a lot, you kind of are wasting gas.