Page 11 of 13

### Re: Hovercraft B/C

Posted: April 9th, 2018, 6:28 pm
photolithoautotroph wrote:
Questions:

### Re: Hovercraft B/C

Posted: April 9th, 2018, 6:55 pm
UTF-8 U+6211 U+662F wrote:
photolithoautotroph wrote:
Questions:

### Re: Hovercraft B/C

Posted: April 9th, 2018, 7:04 pm
Whoops.

Why do horse carriages move when the Third Law says every force has an equal and opposite force?

### Re: Hovercraft B/C

Posted: April 10th, 2018, 9:35 am

### Re: Hovercraft B/C

Posted: April 10th, 2018, 12:51 pm
photolithoautotroph wrote:

Nah, I think rotational motion is fair game. I just haven't gotten to it yet >.>

EDIT: For #1, in order for the ball (EDIT2: to roll), don't you have to apply a torque to it first though?

### Re: Hovercraft B/C

Posted: April 10th, 2018, 5:31 pm
UTF-8 U+6211 U+662F wrote:
photolithoautotroph wrote:

Nah, I think rotational motion is fair game. I just haven't gotten to it yet >.>

EDIT: For #1, in order for the ball, don't you have to apply a torque to it first though?

You can assume that the gravity does all of the work, like it starts on an incline.

### Re: Hovercraft B/C

Posted: April 11th, 2018, 11:48 am
photolithoautotroph wrote:
UTF-8 U+6211 U+662F wrote:
photolithoautotroph wrote:

Nah, I think rotational motion is fair game. I just haven't gotten to it yet >.>

EDIT: For #1, in order for the ball, don't you have to apply a torque to it first though?

You can assume that the gravity does all of the work, like it starts on an incline.

Gravity and the normal force only apply translational motion though (as far as I know), so the only force that would apply torque is friction, which wouldn't be specified.

(Also I asked my q in case you didn't see it)

### Re: Hovercraft B/C

Posted: April 11th, 2018, 12:23 pm
UTF-8 U+6211 U+662F wrote:
photolithoautotroph wrote:
UTF-8 U+6211 U+662F wrote:Nah, I think rotational motion is fair game. I just haven't gotten to it yet >.>

EDIT: For #1, in order for the ball, don't you have to apply a torque to it first though?

You can assume that the gravity does all of the work, like it starts on an incline.

Gravity and the normal force only apply translational motion though (as far as I know), so the only force that would apply torque is friction, which wouldn't be specified.

(Also I asked my q in case you didn't see it)

Momentarily consider the ball to be a rod (same mechanics) and consider the pivot point to be the contact point between the rod and the ground. Friction can be neglected entirely, otherwise I do not believe that the above method of solution works because it neglects the work done by friction (sorry, should have specified in my original post). Because the normal force on the rod acts through the pivot point, the lever arm is zero and this force can be neglected. Thus, the only force acting upon the rod is the weight of the rod, but this weight acts as a torque because it is not acting through the pivot point, which causes the rod to tip over down the incline and fall. Applying this same principle to a ball, this torque would cause the ball to begin rotating.

### Re: Hovercraft B/C

Posted: April 11th, 2018, 3:24 pm
photolithoautotroph wrote:
UTF-8 U+6211 U+662F wrote:
photolithoautotroph wrote:
You can assume that the gravity does all of the work, like it starts on an incline.

Gravity and the normal force only apply translational motion though (as far as I know), so the only force that would apply torque is friction, which wouldn't be specified.

(Also I asked my q in case you didn't see it)

Momentarily consider the ball to be a rod (same mechanics) and consider the pivot point to be the contact point between the rod and the ground. Friction can be neglected entirely, otherwise I do not believe that the above method of solution works because it neglects the work done by friction (sorry, should have specified in my original post). Because the normal force on the rod acts through the pivot point, the lever arm is zero and this force can be neglected. Thus, the only force acting upon the rod is the weight of the rod, but this weight acts as a torque because it is not acting through the pivot point, which causes the rod to tip over down the incline and fall. Applying this same principle to a ball, this torque would cause the ball to begin rotating.

Kind of...

Also, the pivot point of a ball rolling down a surface would be the ball's CoM (the ball rotates around its CoM), and both the force of gravity and the normal force act through the CoM, giving it zero torque. (Source: stackexchange)

EDIT: However, that does work if the ball is rolling without slipping which comes from static friction.

### Re: Hovercraft B/C

Posted: April 15th, 2018, 7:26 am
photolithoautotroph wrote:

(Just to be clear, it's your turn now)

### Re: Hovercraft B/C

Posted: April 15th, 2018, 8:49 am
Sorry for the wait, had to grind to keep my GPA afloat for the past few days.

Question

### Re: Hovercraft B/C

Posted: April 15th, 2018, 10:25 am
Solution

### Re: Hovercraft B/C

Posted: April 15th, 2018, 11:11 am

### Re: Hovercraft B/C

Posted: April 19th, 2018, 7:46 am
Consider a pipe with radius r.

If an ideal fluid is flowing through the pipe, how would the flow rate change if the radius was increased to 2r?

If a non-ideal, viscous fluid is flowing through the pipe, how would the flow rate change if the radius was increased to 2r?

### Re: Hovercraft B/C

Posted: April 19th, 2018, 12:32 pm
Tesel wrote:Consider a pipe with radius r.

If an ideal fluid is flowing through the pipe, how would the flow rate change if the radius was increased to 2r?

If a non-ideal, viscous fluid is flowing through the pipe, how would the flow rate change if the radius was increased to 2r?