Is Speed the Same as Velocity in Physics?

[fatgreypony]

I understand the basics of speed and velocity, but I got a rather backhanded question on a recent test that I believe was marked incorrectly.

Q: A baseball is thrown toward home plate. Is this a speed or a velocity?

I said it was a speed, the ball could have been thrown from anywhere toward home plate. When I asked why it was a velocity, the response was that although the direction is unknown, it still has a direction. But then by that logic, all speeds would be velocities because they have to be traveling in a direction, even if it is not given. Did my teacher screw me over? Where am I going wrong?

 

[symbolipoint]

Without being too picky, speed is a size. Velocity is that size combined with a direction.

Look for the meanings of the words, "scalar", and "vector".

 

[Dale]

I would say it is neither. It is a direction. Speed is a magnitude, and velocity is a magnitude and a direction.

Toward home plate is a valid direction. It means from the baseballs current location draw a line to home plate and the velocity is parallel to that line.

 

[cepheid]

It's definitely a poorly-phrased question. "A baseball is thrown towards home plate. Is this a speed or a velocity?" Well, what does "this" refer to? Does it refer to the action of throwing a ball that was described in the previous sentence? If so, then "this" is neither a speed nor a velocity. It's a description of something that some person did. If you want to ask students to identify the type of a physical quantity, then you have to actually provide a physical quantity in your description. E.g. a ball is moving at 3.0 m/s towards home plate. Is this quantity mentioned above a speed or a velocity? Something like that would have been much better, in my opinion.

 

[PJC01]

I would like to clarify the difference between speed and velocity in this context. Speed refers to the rate at which an object is moving, while velocity includes both the speed and direction of the object's movement.

In the case of a baseball being thrown towards home plate, it is correct to say that it has a speed because it is indeed moving in a certain direction. However, it is not correct to say that it has velocity because the direction of the throw is not specified. Velocity requires both the speed and direction to be known.

Your reasoning is correct in that all objects in motion have a direction, but in order for it to be considered velocity, the direction must be specified. Therefore, it is not fair to say that all speeds are velocities.

It is possible that your teacher may have made a mistake in marking your answer, and I would suggest discussing it with them to clarify the concept. It is important for students to have a clear understanding of scientific concepts, and it is the responsibility of the teacher to provide accurate information and explanations.