20130911

Online reading assignment: projectile motion, forces/interactions

Physics 205A, fall semester 2013
Cuesta College, San Luis Obispo, CA

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing a presentation on projectile motion and forces/interactions.

Selected/edited responses are given below.

Describe something you found interesting from the assigned textbook reading or presentation preview, and explain why this was personally interesting for you.
"Newton's first two laws of motion: everything's either constant or changing. This is relatable in life situations."

"How horizontal velocity is constant in projectile motion."

"How you can add forces to find the net force because I thought it would be more complicated."

"The launch angle, as far as projectile motion is concerned, is the angle between the initial velocity vector and the horizontal."

"That the coefficient of static friction is always larger than the coefficient of kinetic friction for an object on a given surface. I would have thought it the other way around."

"Finding ways to fit the information we are given into the equations. It makes it easier to process information."

"I enjoy trigonometry, and therefore found the use of cosine and sine in the figuring of projectile motion problems to be quite cool."

"If there is no horizontal motion, a projectile is in free fall."

"I found it interesting, but not necessarily surprising, that both equations for tension force and normal force are very similar. I never really took the time to realize that tension force and normal force are so similar. The videos attached really helped and were also extremely interesting examples!"

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"That the magnitude of the static friction force can vary from zero (no or barely trying to unstick an object) up to a maximum value."

"Having trouble matching which equations to use in what circumstances."

"So, adding forces is literally just F1 + F2 = total (net) force."

"Confused on how horizontal velocity is able to stay constant for projectile motion, while vertical velocity changes."

"Static and kinetic force equations."

For all possible cases of an object during ideal projectile motion, its horizontal speed will be:
decreasing.  ******* [7]
constant.  ******************************** [32]
increasing.  *** [3]
(More than one of the above choices.)  *** [3]
(Unsure/guessing/lost/help!)  * [1]

Describe a situation with a negative (starting) angle of elevation for projectile motion.
"While standing on a cliff, you throw a rock a bird that is flying below you."

"A cannon fired down upon attacking troops storming the bottom of a fort."

"I honestly don't know."

"A rock rolling down a hill that ends in an abrupt drop off."

"When a seagull drops a clam while in flight, the clam drops at an angle."

"I couldn't come up with a situation."

"When someone with a bow is shooting an arrow at a target lower than his/her position."

When a pitcher throws a baseball."

"Throwing a ball down towards a wall to have it bounce back."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"For projectile motion, is the horizontal acceleration zero and horizontal speed constant?" (Yes!)

"Blah." (Only partial credit for comments such as this.)

"From your blog:
Newton's third law has nothing to do with motion or net force, but something else entirely, something much more universal and encompassing than considering a particular type of motion or net force...
What is it?!? The suspense is killing me!" (Newton's third law deals with a fundamental property of all forces--that they are interactions between two objects. Doesn't sound like a big deal, but oh yes, it is.)

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