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# Physics/Constant Velocity

Question
What are some real world examples of constant velocity?

Hello John,

If an object has constant velocity, its speed is not changing and its direction is not changing.

Examples:
1. A ping pong ball dropped off a tall building will quickly reach a speed where the air drag exactly cancels its weight, so its speed is constant the rest of the way down. If there is no wind that day, it will fall straight down - so it can be called constant velocity.
2. You are pushing a cart along a hallway as you walk at your normal walking speed. (Rather than just describe you walking, I include the cart in this example to avoid the objection that your center of mass has some up and down with each step.)
3. A ball is thrown up at an angle of 10 degrees from vertical. Picture its vertical velocity separately from its horizontal velocity. The value of its vertical velocity will decrease to zero at the highest point and continue decreasing into negative numbers on the way down. But the horizontal velocity will remain constant - and of course will be horizontal the whole time. If you like, imagine the ball's shadow. If the ground is flat and level, the velocity of ball's shadow will have constant speed and constant direction.

There could be minor objections to all of these examples. Not much is perfect in this world. Do you walk at a constant velocity? Not if the measurement is accurate enough. There would be minor variations. Especially in Introductory Physics, we sometimes avoid looking at minor complications to simplify the analysis.

I hope this helps,
Steve

Physics

Volunteer

#### Steve Johnson

##### Expertise

I would be delighted to help with questions up through the first year of college Physics. Particularly Electricity, Electronics and Newtonian Mechanics (motion, acceleration etc.). I decline questions on relativity and Atomic Physics. I also could discuss the Space Shuttle and space flight in general.

##### Experience

I have a BS in Physics and an MS in Electrical Engineering. I am retired now. My professional career was in Electrical Engineering with considerable time spent working with accelerometers, gyroscopes and flight dynamics (Physics related topics) while working on the Space Shuttle. I gave formal classroom lessons to technical co-workers periodically over a several year period.

Education/Credentials
BS Physics, North Dakota State University
MS Electrical Engineering, North Dakota State University