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Blog post: swansont: Beyond Death and Taxes

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One more thing is certain: some beginners will trip up on physics concepts. It's a new way of thinking, and it takes getting used to.

 

Dot Physics: Constant Force and Constant Motion

 

It seems that every semester when this discussion comes up, someone says this:

 

“Well, I think that a constant force will make the thing go at a constant speed. It just makes sense. Look at your car. You push on the gas pedal with a constant force and the car goes at a constant speed.â€

 

For some reason, the students think of pushing the gas pedal with a constant force as the same as pushing the CAR with a constant force. Perhaps this is because the gas pedal is part of the car. Maybe they are just trying to bring one of their own experiences into the discussion.

 

I don't think that this is unreasonable — a constant amount of gas to the engine should mean a constant force. But it's not the only force, since there is air resistance and rolling friction balancing the effect of the engine. I think that the problem is more the difficulty in conceptualizing a single force without any other forces on the object — we don't have much experience driving in a vacuum.Read and comment on the full post

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