If you put 2 pennies on a record player...

frankmatthews

frankmatthews

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If you put 2 pennies on a vinyl record, one near the outter edge and one near the center by the label and start the record player, both pennies are traveling the same speed but the outter penny is making a larger circle and thus traveling farther than the inner penny. They both make a circle in the same amount of time going the same speed even though one is traveling a greater distance. How?
 
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The one closest to the center is NOT traveling at the same speed. Is inherently moving slower.

Ex: when you swing a bat the very end of the bat is actually moving faster then say your elbow, thus making it more powerful.

You hit the baseball at the "sweet spot" of the bat, not by your hands
 
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The pennies are actually traveling the same speed, just the inner circle perimeter is a much smaller perimeter than the edge circle, which means the penny on the inner circle will travel a miniscual distance compared to the outer penny, making it look slower and thus making them finish a full circle at the same time.
 
You can't just assume they're going the same speed without defining/specifying the kind of "speed" you're looking for in this particular situation.

This is a rotational motion problem, thus there are two types of speed to be accounted for: the angular speed/velocity w and the linear speed/velocity v. If we're talking angular speed, then they are both indeed going the same speed and traveling the same distance. If we're talking linear velocity, then the outer penny is traveling at a higher speed and distance.




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SuperAntigen said:
You can't just assume they're going the same speed without defining/specifying the kind of "speed" you're looking for in this particular situation.

This is a rotational motion problem, thus there are two types of speed to be accounted for: the angular speed/velocity w and the linear speed/velocity v. If we're talking angular speed, then they are both indeed going the same speed and traveling the same distance. If we're talking linear velocity, then the outer penny is traveling at a higher speed and distance.




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Click to expand...

/thread

Lock this up. Bout to have flashbacks to college physics
 
speed is a measure of distance/time
the outer penny is traveling a greater distance over the same amount of time, therefore it has a greater speed
next question
 
Different points on a rotating rigid body move different distances in a given
time interval, depending on how far each point lies from the rotation axis. But
because the body is rigid, all points rotate through the same angle in the same
time . Hence at any instant, every part of a rotating rigid body has the
same angular velocity.
 
i bet this question would have been answered with "illumanati" on the other site...

dumb ^$^^$ asking dumb questions,,,
 
Their angular velocity is equal because they are travelling the same amount of degrees. 

Their tangential velocity is different since the radius of their circle is different since circumference = 2*pi*radius
 
The angular velocity is the same for any point on a rigid body. 

In this instance, the object is rotating about a fixed axis at its center. The velocity is zero here.

From kinematics, we know that the velocity of any point, relative to the center, has to equal the distance of that point from the center times the angular velocity.

Therefore, two points that are different distances from the center are not traveling at the same speed. 

I think.
 
FIRE said:
The pennies are actually traveling the same speed, just the inner circle perimeter is a much smaller perimeter than the edge circle, which means the penny on the inner circle will travel a miniscual distance compared to the outer penny, making it look slower and thus making them finish a full circle at the same time.
Click to expand...
 
jordan23dotcom said:
The one closest to the center is NOT traveling at the same speed. Is inherently moving slower.

Ex: when you swing a bat the very end of the bat is actually moving faster then say your elbow, thus making it more powerful.

You hit the baseball at the "sweet spot" of the bat, not by your hands
Click to expand...

Solid first reply.
 
FrankMatthews said:
I don't think any of you have it right yet, but keep tfying.
Click to expand...
Trust me fam, I got it right. I'm an Engineering Major so this is ALL I do. 

Just take a look at the units. Angular velocity = rad/s. Tangential velocity = m/s. They are traveling the same amount of angle in a given time therefore their angular velocities are the same. To turn angular velocity into a tangential velocity, you multiply by 2*pi*radius (circumference). Since their radii are different, their tangential velocity is different.

A unit analysis goes a LONG way. Extremely helpful in solving problems.

Might want to look into Buckingham's Pi Theorem.
 
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