The following are real quik demos to be used either as individuals or, as I do them, as rapid fire demos that will get the kids involved quickly.
Hey, You just HIT me! Have a kid break a
meter stick over your forearm (get the idea I enjoy pain?) or even just
another meter stick. Kid swings like an overhead Ax blow to firewood so
that contact is made around the 50 cm mark and on the FLAT edge of his
m-stick. If its your arm, stick breaks and kids go, "Ooooo". Safety Note: Have all kids within a few meters of you wear goggles. Maple meter sticks sometimes shatter and splinters fly around. Cool effect, but you really don't want to hurt your kids, do you? Too much paperwork... If
it's another m-stick, hold it so it is vertically aligned - this allows
his stick and yours to be perpendicular. Good example of Inertia. The 50
cm mark of his stick is "told" to stop, but the end of the
stick isn't told yet, so it continues to move fast. What happens to wood
when one part is told to move and another isn't? SNAP!
Hey, You just HIT me, PART 2! I do this one all by my lonesome at the front desk. There's just something about one of my students swings a hammer at my hand while it's flat on the demo desk that scares me. Call me a chicken, but...
Just like the meter stick thing above, this is cool! Obtain a brick. A regular red construction brick works. I use the grey landscaping bricks since I have a batch left over from a job I was supposed to do in my back yard...I'll get to it...tomorrow... Anyway, lay the brick on your hand or forarm which is flat on the desk top. Smack the brick HARD with a hammer. The brick breaks in half, the kids go, "OOOooooo", and you are absolutely unharmed. Why?
Just like the cinder block broken on my chest while on a bed-O-Nails, see Bed Of Nails Demo, the brick has lots of inertia and wants to stay stationary. The hammer, which also has lots of inertia, is telling the brick to get out of the way. The brick says, "NOT!" and stays put. However, the force from the hammer causes deformity and the brick snaps - usually in half right around your hand or arm. Cool.
Wet Relay Race This will demo that even liquids have inertia. I pick three teams of two kids each to have a simple relay race. Distance is about 10m. They must run to the determined point, usually another student standing there, run around the point, return to his/her partner and "tag" off so the 2nd person can do his race. However, they must carry with them a FULL beaker of water! The more they spill, the more points they lose. I give 5 points to the winner, 3 to 2nd place, and 1 to the 3rd - LOSER! Then I deduct a point for each 10 ml missing from the FULL TO THE BRIM 500 ml beaker. Most often, the winner even has a negative score.
This shows the "sloshing" of liquids, like coffee in a car ride, is just a result of it's own inertia telling it to stay put! The kids then have to explain where they lost the water and why.
Doll Fight! Use dolls or stuffed
animals (I use original Cabbage Patch (TM) Dolls) to demonstrate the
physics of a seatbelt - INERTIA. Have one hop on a dynamics cart, or roller-skate,
and head down a ramp that has a large brick wall at the bottom. Upon the
cart hitting the wall, the cart stops, but the doll continues and is
"hurled" over the wall and the cliff (my desk edge, actually).
The other doll had physics and straps on his seatbelts. In this case,
lots and lots of duct tape. Upon smashing into the wall, he/she is still
a part of the object and is thus saved the ignoble end of cliff flying. This leads nicely into seatbelt safety. Your better kids will make the connection. This is a good thing.
Use NFL Football clips
to show that the heads of the Q-backs actually DON'T get snapped back
when tackled. The head actually stays there while the rest of the body is
pushed out from under it. Same injury, just not caused the way they
Card-N-Coin: I do this using a beaker, index card, and penny. You can purchase a specific set-up for about $30 from any science supply house, but... Place the card ontop of the beaker with the penny ontop of the card in the center of the beaker. Flick the card out as fast as you can. The penny will drop into the beaker. Why? Inertia.
Hoop-n-Marker: I just got this one from Amy Durden of Savannah Christian Preparatory School, Savannah, GA. It's a cool twist on the ole Card-N-Coin trick above. In her words -
Buy an embroidery hoop at Walmart for 64 cents. It's 10 inches or so in diameter.
Buy and drink a fruit drink in a bottle. The opening should be a little more than an inch. I like Mystic or Fruitopia. Any flavor.
Grab a dry erase marker.
Balance the inside circle of the hoop (discard the outer ring) on the open mouth of the bottle and the marker on top of the hoop. (hardest part of the demo) Yank the hoop out from under the marker (fast and straight sideways) and the marker will fall into the bottle 10 inches below. My kids think its SOOO cool. It's easier to see from a distance than the index card and nickle trick I used to use. If you like the trick, buy several hoops because they break easily.
Hammering Studs: Place 3 or 4 hunks of 2x4 stud wood on top of each other on your lab desk. Smack the bottom one, going in the direction of the long side, smartly with a hammer. Note, the bottom one moves out of the way while the others above just drop down in place in a pile. Cool.
Roller Skating with The Fat Guy: This is always fun for me. This works BEST with a volunteer or two bringing in their inline skates. Otherwise, just use some sturdy collision carts that will hold a kids weight - I have some of those old wooden ones that even hold me. These demos can also be done in conjunction with Newt's 2nd and 3rd Laws.
1. While a SMALL kid (to me they are ALL small...) stands in front of you with skates on both you and the kid, push on the kid's shoulders with enough force to cause motion. BE CAREFUL, small children sometimes don't need lots of force to fly across the room! Note, the kid moves backward a much larger distance than you. Keep in mind, I am 250-ish. Most of my kids are in the mid 100's. This works for me all the time. If you are on the small-ish side, pick a LARGE kid and YOU move, not him. Same effect, different direction.
2. Do this in reverse IF the kid and you (or two kids, if you choose.) are OK skaters. Head toward each other with enough speed to actually notice a change. It doesn't have to be blazing speed, but fast enough to note a change in speed when you collide. Grab onto each other upon contact. Note, if the mass difference is large enough and the speeds were the same, the "group" now moves in the direction of the larger person. The little guy got "gobbled up".
3. HOVERCRAFT - I use a home-made hovercraft, see my hovercraft page, to demo 1st Law. This is absolutely GREAT due to the "lack" of friction and it's actually quite dramatic!
Wile E. Coyote: I use video clips extensively. Here, you can pick just about ANY cartoon to show what DOESN'T happen. Wile E. Coyote, that persistent carnivore from the desert, disobeys Newt's 1st Law vertually all the time.
Also, don't forget the movies! For Newt's 1st Law, one of the good clips is from Star Trek IV, The Voyage Home. This is the one where the ONLY true Star Trek crew has to go back into the past - OUR current time - to pick up some whales to save the world of the future. Silly storyline, I know, but still a good flick. Toward the beginning of the movie, this huge alien probe is sucking all the EM energy out of space ships and satellites as it passes. There is a scene where two shuttles are flying thru space, lose their energy - lights go out and the engines stop (I know, you HEAR them...) - and come to a screeching halt!
This blatantly disobeys Newton! The shuttles would still move forward in a stright line at their last speed. Why can't these Hollywood guys call me for consultation work?
Crash Test Dummy Videos: Obtain a video or DVD of crash testing. These can be obtained free from many sources. Show in SloMo the inertial effects of the passengers AND even the car parts during a crash. I even make this a relevent "seat belt safety" tie-in.
2nd Law Specific Demos
Cart & Mass : Typical FMA demo. Attach a string to a wheeled cart. Run this string over a pulley at the edge of the desk. Not to worry, if you have no pulleys, just use the edge of the desk itself. From the other end of the string, hang a weight. [It's a nice idea here to hang an actual mass 'hanger'; a hooked thingee that will allow you to stack up weights so you can change the hanging mass. Devise something that works for you and your equipment. A simple large paperclip and washers will work in a pinch. The string should be just as long as the table is long (or side). Two demos to do:
These are the two basic premises of Newton's 2nd Law: The acceleration of an object is directly proportional to the force acting on it and inversely proportional to the mass of the object being accelerated...
- Vary the hanging mass but keep the carts mass the same and record the motion of the cart when the hanging mass is released. You should notice that with larger masses, the cart accelerates more.
- Vary the mass of the cart while keeping the hanging mass constant. This can easily be done by simply taping or stacking masses on the cart on the table. You should notice that the acceleration of the cart decreases as the mass of the cart increases.