A force perpendicular to velocity does not change speed?

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Homework Help Overview

The discussion revolves around the effects of a force applied perpendicular to the velocity of an object in motion. The original poster questions why applying such a force does not change the speed of the object, despite the expectation that it would alter both direction and speed.

Discussion Character

  • Conceptual clarification, Assumption checking, Mixed

Approaches and Questions Raised

  • Participants explore the relationship between force, velocity, and speed, questioning the implications of applying a perpendicular force. Some consider the effects of instantaneous forces and impulsive forces, while others clarify the distinction between speed and velocity.

Discussion Status

The discussion is ongoing, with participants providing insights and clarifications regarding the nature of speed and velocity in relation to applied forces. There is a mix of interpretations being explored, particularly concerning the effects of instantaneous forces and the definitions of speed and velocity.

Contextual Notes

Some participants express confusion regarding the definitions of speed and velocity, and there is mention of potential misunderstandings in the application of physical principles. The original poster's question reflects a common point of confusion in physics regarding the effects of forces on motion.

mackygood
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Homework Statement



There's a ball moving at a constant velocity V and I apply a force perpendicular to the direction of the velocity. Why is it that there's no change in speed?

If I add a perpendicular force, there would be a new vector thus resulting in a new velocity with a different direction and speed right?

http://img22.imageshack.us/img22/8261/forceh.jpg \[/URL]

Thanks for any answers :D
 
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In order to keep the speed unchanged and only change the direction of motion, the force must be kept perpendicular to the velocity as the velocity changes. Your picture shows an initial upward velocity and a sideways force. As soon as the velocity starts changing direction, so must the force. This is not illustrated in your diagram.
 
thanks for your reply!

What if the force was instantaneous? Would it still not affect the speed?
 
mackygood said:
What if the force was instantaneous? Would it still not affect the speed?
I'm not sure what you mean by "instantaneous". If you mean something like an impulsive force (a quick push to the side that lasts a short time), then that could certainly change the speed since it would not be continually adjusted to be perpendicular to the velocity.
 
I think you are confusing velocity and speed. A perpendicular force will not increase velocity but it will increase speed.
 
skeptic2 said:
A perpendicular force will not increase velocity but it will increase speed.
A perpendicular force will not change the speed but will change the velocity.
 
If an object is traveling upwards at velocity v and at point p it is influenced by force f in the horizontal direction, its velocity [in the upwards direction] is unchanged but its speed has increased to √(v^2 + f^2).
 
skeptic2 said:
If an object is traveling upwards at velocity v and at point p it is influenced by force f in the horizontal direction, its velocity [in the upwards direction] is unchanged but its speed has increased to √(v^2 + f^2).
Among your many clues that this cannot possibly be correct is that you're adding two quantities with different units.
 
Hurkyl said:
Among your many clues that this cannot possibly be correct is that you're adding two quantities with different units.

Yes, that was a pretty stupid mistake. I wasn't thinking about what I was writing. What were the others?
 

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