Blast Off!

A few of the rockets my students made.

The eighth graders are done with middle school and are moving on.  During the last few days we completed our Forces and Motion unit by building rockets and shooting them off.  Mr. S has done this for years.  He build his own rocket launcher using PVC pipe and an air pump.  The rockets shoot off from all of the air pressure built up.  He has extra PVC pipes to use when building the rocket so the kids can make sure they have the correct diameter needed.

The day we made these was also my birthday.  I received some nice wishes and a note on my whiteboard:

They're simple rockets made from card-stock paper, but it was lots of fun.  A few of the kids made rockets that flew up really high and over the school fence. Most went a little ways up.  Others totally failed and only the top cone blew off and the rest of the rocket remained.  It was a fun last activity, though.

Mr. S ready to blast off another rocket.

8th Grade Final Exam

It's been a while.  But I feel the end of the year is like that.  I'm not really going over anything new, we're just reviewing everything we've already done.  And then there are a lot of activities and meetings towards the end of the year.

Does anyone else feel like the end of the year is both a drag (still 3 more weeks left??) and a sprint to the finish (only 3 more weeks left??)?

Today my eighth graders took their final exam.  My first class left me very pleased with the results.  More than half the class received A's and B's.  That's awesome.  I don't give easy tests and I expect a lot.  So I was very pleased.

My second class was not as good. Only one kid passed, and he passed with a 95%.  How can there be that much difference?  This class is hard to control, they're often yelling at each other, and don't always try their best.  Even during the exam they were asking why they couldn't take notes (um, you don't even have any??) because "all" of the other classes let them use notes.  Well, looking from experience, I've never let you use notes on a test, so why would I let you use notes now?  I want to see how much you have learned, not how well you can take and read your notes.  Needless to say this second period was difficult and hard.  I don't think I'm entirely to blame, but I do have a lot of notes on how I'm going to improve next year.

After all, I'm a brand new teacher.  There is much room for improvement.

Here's my copy of the eighth grade exam.  I was quite pleased with it.  :)

How well would you do on an eighth grade science test?

Explain the Forces

The first day I introduced forces, I also did this worksheet with the kids. We all discussed it together to come up with the answer.  I would write the answer down on my paper that the kids could see on the projector, and they would also write the answer down on their papers.  The last part I had them do themselves.  It's a pretty self-explanatory worksheet, so you can let your kiddos do it on their own if you want.  My reasoning for doing it with them was to have a little more guided practice to let them become confident in the idea before they did their own worksheet.

Again, disclaimer: This is not mine!  I found this on one of those wonderful teaching websites with free worksheets, but I wasn't good enough to trace my sources so I can't link you to the original website.

Get the worksheet at the bottom of the page.

I had a few kids telling me that was their car, and asking how I got a picture of it. :P

What is a Force?

I have loved this unit with the 8th graders.  There's something concrete about this idea that the kids can really hold on to.

To start out this unit, I first introduced the fact that

a force has both magnitude and direction.

I started out by holding a book up in front of me, then quickly letting go and catching it again lower down.

Question:  Why does it fall?
Answer: Gravity.
Question: Gravity is doing what to the book?
Answer: pulling it down.

Okay, so now we know that there is a force of gravity with some magnitude in the direction towards the ground.

Now the book is placed on a table.

Question: Is there still gravity on this book?

I got some weird looks with that.   . . . . . No?  . . .  Yes? . . . . I don't really know, but I think so, but it's not moving down. . . .?????

When the kids say "no," my eyes get real big and I say, "What?? There is no gravity anymore??"  And the kids say "okay, yeah, there is."

Question:  Then why is the book not falling down?
Answer: Because the table is in the way.

Oh!

Introduce this image on the smart board:

So we know there's gravity pulling it down. (Draw downward arrow).  But the book isn't falling through the table, so the table must be pushing up on the book. (Draw upward arrow).

HuUh??!?

Yes.  The table is pushing up on the book.  At this point you take the book back into your hands.

Question: Am I holding the book up with a force?
Answer: Yes.
Question: Then doesn't it make sense that the table also has to hold the book up with a force?
Answer: I guess so.

Then you do a whole bunch of other examples demonstrating the forces and which direction they are going. Examples can be cars, balloons, something falling (this was done to introduce the idea of air resistance), other things sitting motionless.

Now you introduce the idea that you can combine forces to find a net force.

SCENARIO 1

Here's a wonderful little picture analogy.  I chose a girl in the class to be the first person.  Sammy* (*names has been changed) is driving along the road when suddenly she runs out of gas.  She gets out and sees a gas station at the end of the road so tries to push her car.  But the car is too heavy for her to push and it won't budge.  She calls her friend (motion to Sammy for her to give her desired friend's name), Brittany*.  Brittany comes and tries to help, but they are both still not strong enough to push the car.  They then call a third friend (motion again for them to choose a third comrade) who comes and they all push with all their might.  They're finally able to get the car rolling.

Truth:

Students are more likely to listen when you use their name for an analogy.

Kids can easily see that because there are three people there is more force and the car will move.

Do lots of examples like this where you practice adding the forces, stressing that the forces are all going the same direction so you can add them.  Your answer must have both magnitude and direction.  I don't want "24N".  I want "24N ->"

SCENARIO 2

Tug-of-War.  Who doesn't love a good tug-of-war?

Team A is pulling with a combined force of 20N <-- to the left.  Team B is pulling with a combined force of 30N --> to the right.  

Question: Are the teams pulling in the same direction, or in the opposite direction?

Answer: Opposite direction.

Question: So do you think we're going to add their forces or subtract their forces?

Answer: subtract.

The net force is 10N --> to the right. 

Question: Why is the rope going to the right?

 .. . . pause while students try to figure this out . . 

timid student answer: because the team on the right is stronger?

YAY!  (remember that this is SPED, so kids need time to process answers). 

More tug-of-war examples with net forces to the right, to the left, and a net force of 0.

More examples like this on the board where both I model and the kids practice as a group:

Remember, the answer is 4N -->, not just 4N.

Independent Practice

Disclaimer, this is not my worksheet.  I found this fabulous worksheet online that I thought was just perfect for what we were doing.  I don't remember what website I got it off of, but it was one of those great teaching resource websites with free worksheets.  

To get worksheet, click here.

I printed the first two pages double sided for this day.  I printed pages 3-4 for another day to keep up practice.