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__not__zero, but its speed remains constant.

I don't know if this situation is possible to explain.

- Thread starter crysland
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I don't know if this situation is possible to explain.

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Doc Al

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What does Newton's 1st law say?

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- #4

Doc Al

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Good. Note the key wordvelocityunless acted on by a net external force.

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Velocity has both magnitude and direction but speed doesn't have direction

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Doc Al

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Exactly! So see if you can try to answer the question now.Velocity has both magnitude and direction but speed doesn't have direction

Give an example of something with constant speed but

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A car going in a circle.

- #8

rcgldr

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How about a car following any curved path while moving at constant speed? A section of road could be similar to a sine wave, ellipse, spiral, parabola, ..., and a car would be able to follow that path while moving at constant speed.A car going in a circle.

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arildno

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Your answer is definitely correct!A car going in a circle.

But, as the next post shows, other similar situations also exist.

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Ok so what is the net external force acting on the car?

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arildno

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Do you remember the expression for centripetal acceleration?Ok so what is the net external force acting on the car?

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Yes. So centripetal force that pulls it toward the center is external?

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arildno

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Certainly.

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rcgldr

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That would be speed^2 / (radius of curvature), which gets complicated for paths other than a circle.Do you remember the expression for centripetal acceleration?

The simple answer is that centripetal force = centripetal acceleration x mass of the car.Yes. So centripetal force that pulls it toward the center is external?

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