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If an object is traveling in a straight direction at a constant speed it has no acceleration, right?

So if $F=ma$ and $a =0$ then force should equal 0.

Does that mean a car traveling at a constant speed (no accelerating) has no force?

Does it only have force when it hits an object (and thus decelerates quickly?)

Qmechanic
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Anchower
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1 Answers1

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That is partially correct. You are missing a critical part of Newton's 2nd law: $F_{net} = m a$. It's not just any one force that equals the mass times the acceleration. It's the "net force" - the vector sum of all the forces. So a car that is traveling at a constant speed may have many forces on it (gravity, the normal force, friction, air resistance, etc), but they all add up to zero - they balance each other out, so that $F_{net} = 0$.

If the car then hits an object (in your example) and therefore decelerates, then the forces are no longer balanced, they no longer add up to zero, and the car does change its speed - it experiences acceleration.

Brionius
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